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TABLE OF CONTENTS
TABLE OF CONTENTS

As filed with the Securities and Exchange Commission on December 11, 2018

Registration No. 333-228156

UNITED STATES
SECURITIES AND EXCHANGE COMMISSION
Washington, D.C. 20549

Amendment No. 1
to

FORM S-4
REGISTRATION STATEMENT
UNDER
THE SECURITIES ACT OF 1933

Antero Midstream GP LP
to be converted as described herein into a corporation named

Antero Midstream Corporation

(Exact name of Registrant as specified in its charter)

Delaware
(State or other jurisdiction of
incorporation or organization) 4922
(Primary Standard Industrial
Classification Code Number) 61-1748605
(I.R.S. Employer
Identification Number)

1615 Wynkoop Street
Denver, Colorado 80202
(303) 357-7310

(Address, including zip code, and telephone number, including area code, of registrant's principal executive offices)

Glen C. Warren, Jr.
1615 Wynkoop Street
Denver, Colorado 80202
(303) 357-7310

(Name, address, including zip code, and telephone number, including area code, of agent for service)

Copies to:

Douglas E. McWilliams
Lande A. Spottswood
Vinson & Elkins L.L.P.
1001 Fannin Street, Suite 2500
Houston, Texas 77002
(713) 758-2222

Approximate date of commencement of proposed sale of the securities to the public: As soon as practicable after this Registration Statement becomes effective and all other conditions to the proposed transactions contemplated by the Simplification Agreement, dated October 9, 2018, described in the enclosed joint proxy statement/prospectus, have been satisfied or waived.

           If the securities being registered on this Form are being offered in connection with the formation of a holding company and there is compliance with General Instruction G, check the following box.    o

           If this Form is filed to register additional securities for an offering pursuant to Rule 462(b) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

           If this Form is a post-effective amendment filed pursuant to Rule 462(d) under the Securities Act, check the following box and list the Securities Act registration statement number of the earlier effective registration statement for the same offering.    o

           Indicate by check mark whether the registrant is a large accelerated filer, an accelerated filer, a non-accelerated filer, smaller reporting company, or an emerging growth company. See the definitions of "large accelerated filer," "accelerated filer," "smaller reporting company," and "emerging growth company" in Rule 12b-2 of the Exchange Act.

Large accelerated filer o Accelerated filer o Non-accelerated filer ý Smaller reporting company o Emerging growth company ý

           If an emerging growth company, indicate by check mark if the registrant has elected not to use the extended transition period for complying with any new or revised financial accounting standards provided pursuant to Section 7(a)(2)(B) of the Securities Act. ý

           If applicable, place an X in the box to designate the appropriate rule provision relied upon in conducting this transaction:

           Exchange Act Rule 13e-4(i) (Cross-Border Issuer Tender Offer) o

           Exchange Act Rule 14d-1(d) (Cross-Border Third-Party Tender Offer) o

CALCULATION OF REGISTRATION FEE

Title of each class of securities to be registered	Amount to be registered(1)	Proposed maximum offering price per share	Proposed maximum aggregate offering price(2)	Amount of registration fee(3)
Common stock, par value $0.01 per share	373,541,369	N/A	$8,524,383,489.69	$1,033,156

(1)

Represents the maximum number of shares of common stock, par value $0.01 per share, of Antero Midstream Corporation ("New AM") estimated to be issuable upon the completion of the Conversion (as described herein) and the Merger (as described herein).

(2)

The proposed maximum aggregate offering price was calculated based upon the market value of the common shares of Antero Midstream GP LP ("AMGP" and, such common shares, the "AMGP Common Shares"), the securities to be converted into common stock of New AM in connection with the Conversion, and common units of Antero Midstream Partners LP ("Antero Midstream" and, such common units, the "AM Common Units"), the securities to be converted into the right to receive the Merger Consideration (as described herein) in the Merger, in accordance with Rules 457(c) and 457(f) under the Securities Act of 1933, as amended as follows: the sum of (i) the product of (a) $15.87, the average of the high and low prices of the AMGP Common Shares as reported on the New York Stock Exchange (the "NYSE") on October 30, 2018 and (b) 186,219,438, the estimated maximum number of AMGP Common Shares that will be converted into common stock of New AM in connection with the Conversion, and (ii) the product of (a) $29.73, the average of the high and low prices of the AM Common Units as reported on the NYSE on November 1, 2018 and (b) 187,321,931, the estimated maximum number of AM Common Units that may be exchanged for the Merger Consideration in the Merger.

(3)

The registrant previously paid $1,032,177 of the total registration fee in connection with the previous filing of this Registration Statement.

The registrant hereby amends this Registration Statement on such date or dates as may be necessary to delay its effective date until the registrant shall file a further amendment which specifically states that this Registration Statement shall thereafter become effective in accordance with Section 8(a) of the Securities Act or until this Registration Statement shall become effective on such date as the Securities and Exchange Commission (the "SEC"), acting pursuant to said Section 8(a), may determine.

The information in this preliminary joint proxy statement/prospectus is not complete and may be changed. Antero Midstream Corporation may not distribute or issue the securities being registered pursuant to this registration statement until the registration statement, as filed with the Securities and Exchange Commission (of which this preliminary joint proxy statement/prospectus is a part), is effective. This preliminary joint proxy statement/prospectus is not an offer to sell nor should it be considered a solicitation of an offer to buy the securities described herein in any state where the offer or sale is not permitted.

PRELIMINARY—SUBJECT TO COMPLETION DATED DECEMBER 11, 2018

CONVERSION AND MERGER PROPOSED—YOUR VOTE IS VERY IMPORTANT

            On October 9, 2018, Antero Midstream GP LP ("AMGP"), Antero Midstream Partners LP ("Antero Midstream") and certain of their affiliates entered into a Simplification Agreement, as may be amended from time to time (the "Simplification Agreement"), pursuant to which, among other things, (1) AMGP will be converted from a limited partnership to a corporation under the laws of the State of Delaware, to be named Antero Midstream Corporation (which we refer to as "New AM" and the conversion, the "Conversion"); (2) an indirect, wholly owned subsidiary of New AM will be merged with and into Antero Midstream, with Antero Midstream surviving the merger as an indirect, wholly owned subsidiary of New AM (the "Merger") and (3) all the issued and outstanding Series B Units representing limited liability company interests of Antero IDR Holdings LLC ("IDR Holdings"), a partially owned subsidiary of AMGP and the holder of all of Antero Midstream's incentive distribution rights, will be exchanged for an aggregate of approximately 17.35 million shares of New AM Common Stock (as defined below) (the "Series B Exchange"). The Conversion, the Merger, the Series B Exchange and the other transactions contemplated by the Simplification Agreement are collectively referred to as the "Transactions." As a result of the Transactions, Antero Midstream will be an indirect, wholly owned subsidiary of New AM, and former AMGP Shareholders (as defined herein), AM Unitholders (as defined herein) and holders of Series B Units will each own shares of New AM's common stock, par value $0.01 per share (the "New AM Common Stock").

            The board of directors (the "AM Board") of Antero Midstream's general partner, Antero Midstream Partners GP LLC ("AMP GP"), and the conflicts committee of the AM Board (the "AM Conflicts Committee") each has determined in good faith that the Transactions are in the best interests of Antero Midstream and the Disinterested AM Unitholders (as defined below), and have unanimously approved the Simplification Agreement and the Transactions. The board of directors of AMGP's general partner (the "AMGP Board") and the conflicts committee of the AMGP Board (the "AMGP Conflicts Committee") each has determined in good faith that the Transactions are in the best interests of AMGP and the Disinterested AMGP Shareholders (as defined below), and have unanimously approved the Simplification Agreement and the Transactions.

            If the Transactions are completed, in exchange for each common unit representing a limited partner interest in Antero Midstream (each an "AM Common Unit") held, each AM Unitholder other than Antero Resources Corporation ("Antero Resources") (collectively, the "AM Public Unitholders") will be entitled to receive, at its election and subject to proration, one of (i) $3.415 in cash without interest and 1.6350 shares of New AM Common Stock (the "Public Mixed Consideration"), (ii) 1.6350 shares of New AM Common Stock plus an additional number of shares of New AM Common Stock equal to the quotient of (A) $3.415 and (B) the average of the 20-day volume-weighted average trading price per common share representing limited partner interests in AMGP (each, an "AMGP Common Share") prior to the Election Deadline (as defined herein) (the "AMGP VWAP"), or (iii) $3.415 in cash plus an additional amount of cash equal to the product of (A) 1.6350 and (B) the AMGP VWAP. In exchange for each AM Common Unit held, Antero Resources will be entitled to receive, subject to certain adjustments, $3.00 in cash without interest and 1.6023 shares of New AM Common Stock (the "AR Mixed Consideration"). The aggregate cash consideration to be paid to Antero Resources and the AM Public Unitholders will be fixed at an amount equal to the aggregate amount of cash that would be paid if all AM Public Unitholders received $3.415 in cash per AM Common Unit (the "Public Available Cash") and Antero Resources received $3.00 in cash per AM Common Unit it owns, which is approximately $598 million in the aggregate. If the Public Available Cash exceeds the cash consideration elected to be received by the AM Public Unitholders (the amount of such excess, the "Excess Available Cash"), Antero Resources may elect to increase the total amount of cash it receives as a part of the AR Mixed Consideration up to an amount equal to the Excess Available Cash and the amount of shares it will receive will be reduced accordingly based on the AMGP VWAP. In addition, the consideration each AM Public Unitholder will receive may be prorated in the event that more cash or equity is elected to be received than what would otherwise have been paid if all AM Public Unitholders had received the Public Mixed Consideration and Antero Resources had received the AR Mixed Consideration. Based on the closing price of AMGP Common Shares on                    ,                     , the most recent trading day prior to the date of this joint proxy statement/prospectus, the aggregate value of the Merger Consideration (as defined herein) was approximately $             billion.

            AMGP and Antero Midstream will hold special meetings of their shareholders and unitholders, respectively, in connection with the proposed Transactions. At the special meeting of AMGP Shareholders (the "AMGP Special Meeting"), the AMGP Shareholders will be asked to vote on (i) a proposal to approve the Conversion, including a certificate of conversion and a certificate of incorporation (the "Conversion Proposal"), (ii) a proposal to approve the Simplification Agreement, the Merger and the other transactions contemplated in the Simplification Agreement, including the Series B Exchange (the "AMGP Transaction Proposal"), (iii) a proposal to approve the adoption of a New AM omnibus equity incentive plan (the "LTIP Proposal") and (iv) a proposal to approve the issuance of New AM Common Stock to AM Unitholders and Series B Holders pursuant to the Simplification Agreement (the "Issuance Proposal" and, together with the Conversion Proposal and the AMGP Transaction Proposal, the "AMGP Proposals"). Completion of the Transactions is not conditioned upon approval of the LTIP Proposal. Approval of the Conversion Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares. Approval of the AMGP Transaction Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares held by the AMGP Shareholders other than AMGP's general partner and its affiliates (the "Disinterested AMGP Shareholders"). Approval of both the LTIP Proposal and the Issuance Proposal requires the affirmative vote of holders of a majority of the AMGP Common Shares voted on such proposals at the AMGP Special Meeting. At the AM Special Meeting, the AM Unitholders will be asked to approve the (i) the Simplification Agreement, (ii) the Merger, and (iii) the Transactions (the "AM Merger Proposal"). Approval of the AM Merger Proposal requires the affirmative vote of holders of a majority of (i) the outstanding AM Common Units and (ii) the outstanding AM Common Units held by AM Unitholders other than Antero Midstream's general partner and its affiliates (the "Disinterested AM Unitholders").

We cannot complete the Transactions unless the requisite AMGP Shareholders approve the AMGP Proposals and the requisite AM Unitholders approve the AM Merger Proposal. Accordingly, your vote is very important regardless of the number of AMGP Common Shares or AM Common Units you own. Voting instructions are set forth inside this joint proxy statement/prospectus.

            In light of the fact that certain affiliates of AMGP have interests in the Transactions that are different from other AMGP Shareholders, the AMGP Board formed a conflicts committee, consisting of directors that satisfy the requirements to serve on a conflicts committee set forth in the Agreement of Limited Partnership of AMGP. The AMGP Conflicts Committee and the AMGP Board each recommends that the AMGP Shareholders vote FOR each of the AMGP Proposals. The AMGP Shareholders should be aware that some of the directors and executive officers of AMGP's general partner may have interests in the Transactions that are different from, or in addition to, the interests they may have as AMGP Shareholders.

            In light of the fact that certain affiliates of Antero Midstream have interests in the Transactions that are different from other AM Unitholders, the AM Board formed a conflicts committee, consisting of directors that satisfy the requirements to serve on a conflicts committee in the Agreement of Limited Partnership of Antero Midstream. The AM Conflicts Committee and the AM Board each recommends that the AM Unitholders vote FOR the AM Merger Proposal. The AM Unitholders should be aware that some of the directors and executive officers of Antero Midstream's general partner may have interests in the Transactions that are different from, or in addition to, the interests they may have as AM Unitholders.

            This joint proxy statement/prospectus provides you with detailed information about the proposed Transactions and related matters. You are encouraged to read the entire document carefully. In particular, see "Risk Factors" beginning on page 169 of this joint proxy statement/prospectus for a discussion of risks relevant to the Transactions and New AM's business following the Transactions. See "Special Factors—Interests of Certain Persons in the Transactions" for a discussion of the interests of certain directors and executive officers of AMGP GP LLC, the general partner of AMGP, and AMP GP that are different from, or in addition to, the interests of AMGP Shareholders and AM Unitholders, respectively.

            The AMGP Common Shares are listed on the New York Stock Exchange ("NYSE") under the symbol "AMGP," and the AM Common Units are listed on the NYSE under the symbol "AM." The last reported sales price of the AMGP Common Shares on the NYSE on                        ,             was $            . The last reported sales price of the AM Common Units on the NYSE on                        ,                         was $            .

  
Paul M. Rady
Chairman of the Board of Directors of
AMGP GP LLC and Antero Midstream Partners GP LLC

Neither the Securities and Exchange Commission nor any state securities commission has approved or disapproved of the securities to be issued under this joint proxy statement/prospectus or has determined if this document is truthful or complete. Any representation to the contrary is a criminal offense.

            This joint proxy statement/prospectus is dated                        ,                         and is being first mailed to AMGP Shareholders and AM Unitholders on or about                        ,                         .

Denver, Colorado
            ,            

ANTERO MIDSTREAM GP LP
1615 Wynkoop Street
Denver, Colorado 80202

NOTICE OF SPECIAL MEETING OF COMMON SHAREHOLDERS

To the common shareholders of Antero Midstream GP LP:

        A special meeting (the "AMGP Special Meeting") of holders of common shares ("AMGP Shareholders") representing limited partner interests (the "AMGP Common Shares") in Antero Midstream GP LP ("AMGP") will be held on                                    ,                                     at                         , local time, at 1615 Wynkoop Street, Denver, Colorado 80202, for the following purposes:

•

to consider and vote on a proposal (the "Conversion Proposal") to approve the conversion (the "Conversion") of AMGP from a Delaware limited partnership to a Delaware corporation, to be named Antero Midstream Corporation ("New AM"), including a certificate of conversion and a certificate of incorporation, in connection with the transactions contemplated by the Simplification Agreement (such transactions, the "Transactions"), dated as of October 9, 2018, by and among AMGP, Antero Midstream Partners LP ("Antero Midstream") and certain of their affiliates, as may be amended from time to time (the "Simplification Agreement");

•

to consider and vote on a proposal to approve the Simplification Agreement, the merger of an indirect, wholly owned subsidiary of New AM with and into Antero Midstream as contemplated by the Simplification Agreement (the "Merger"), with Antero Midstream surviving such Merger as an indirect, wholly owned subsidiary of New AM, and the other transactions contemplated by the Simplification Agreement, including the Series B Exchange (as defined in the enclosed joint proxy statement/prospectus) (the "AMGP Transaction Proposal");

•

to consider and vote on a proposal to approve the adoption of a New AM omnibus equity incentive plan (the "LTIP Proposal"); and

•

to consider and vote on a proposal to approve the issuance of New AM common stock pursuant to the Simplification Agreement (the "Issuance Proposal" and, together with the Conversion Proposal and the AMGP Transaction Proposal, the "AMGP Proposals").

        Approval of the Conversion Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares. Approval of the AMGP Transaction Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares held by the AMGP Shareholders other than AMGP's general partner and its affiliates (the "Disinterested AMGP Shareholders"). Approval of the Issuance Proposal requires the affirmative vote of holders of a majority of the AMGP Common Shares voted on such proposal at the AMGP Special Meeting. We cannot complete the Transactions unless the requisite AMGP Shareholders approve the AMGP Proposals. Accordingly, your vote is very important regardless of the number of AMGP Common Shares you own.

The board of directors of AMGP's general partner (the "AMGP Board") and the conflicts committee of the AMGP Board (the "AMGP Conflicts Committee"), which consists of two members of the AMGP Board who satisfy the requirements to serve on a conflicts committee under AMGP's partnership agreement, each has determined in good faith that the Transactions are in the best

interests of AMGP and the Disinterested AMGP Shareholders. The AMGP Conflicts Committee and the AMGP Board each recommends that the AMGP Shareholders vote FOR the Conversion Proposal, FOR the AMGP Transaction Proposal and FOR the Issuance Proposal. For more information regarding the recommendation of the AMGP Conflicts Committee and the AMGP Board, see "Special Factors—Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions."

        AMGP Shareholders should be aware that some of the directors and executive officers of AMGP's general partner may have interests in the Transactions that are different from, or in addition to, the interests they may have as AMGP Shareholders. See "Special Factors—Interests of Certain Persons in the Transactions."

        Approval of the LTIP Proposal requires the affirmative vote of holders of a majority of the AMGP Common Shares voted on such proposal at the AMGP Special Meeting. Completion of the Transactions is not conditioned upon approval of the LTIP Proposal. Even if the AMGP Shareholders approve the LTIP Proposal, AMGP will not adopt a New AM omnibus equity incentive plan unless the Transactions are completed.

The AMGP Board unanimously determined that the approval of the LTIP Proposal is in the best interests of AMGP and the AMGP Shareholders. The AMGP Board unanimously approved the LTIP Proposal and recommends that the AMGP Shareholders vote FOR the LTIP Proposal.

        Only AMGP Shareholders of record at the close of business on                                    ,                         are entitled to notice of and to vote at the AMGP Special Meeting. A list of AMGP Shareholders entitled to vote at the AMGP Special Meeting will be available for inspection at AMGP's offices in Denver, Colorado for any purpose relevant to the AMGP Special Meeting during normal business hours for a period of ten days before the meeting and at the AMGP Special Meeting. References to the AMGP Special Meeting in the enclosed joint proxy statement/prospectus are to the special meeting as may be adjourned or postponed.

YOUR VOTE IS IMPORTANT. REGARDLESS OF WHETHER YOU EXPECT TO ATTEND THE AMGP SPECIAL MEETING, PLEASE SUBMIT YOUR PROXY IN ONE OF THE FOLLOWING WAYS:

•

If you hold your AMGP Common Shares in the name of a bank, broker or other nominee, you should follow the instructions provided by your bank, broker or other nominee when voting your AMGP Common Shares.

•

If you hold your AMGP Common Shares in your own name, you may submit your proxy by:

•

using the toll-free telephone number shown on the proxy card;

•

using the Internet website shown on the proxy card; or

•

marking, signing, dating and promptly returning the enclosed proxy card in the postage-paid envelope. It requires no postage if mailed in the United States.

        The enclosed joint proxy statement/prospectus provides a detailed description of the Transactions and the Simplification Agreement as well as a description of the AMGP Proposals and the LTIP Proposal. You are urged to read the joint proxy statement/prospectus, including any documents incorporated by reference, and the Annexes carefully and in their entirety. If you have any questions

concerning the Transactions or the enclosed joint proxy statement/prospectus, would like additional copies or need help voting your AMGP Common Shares, please contact AMGP's proxy solicitor:

MacKenzie Partners, Inc.
1407 Broadway—27th Floor
New York, New York 10018
Toll free: (800) 322-2885
Collect: (212) 929-5500
proxy@mackenziepartners.com

By order of the Board of Directors of
AMGP GP LLC,

  
Paul M. Rady
Chairman of the Board and Chief Executive Officer
AMGP GP LLC

Denver, Colorado
            ,            

Antero Midstream Partners LP
1615 Wynkoop Street
Denver, Colorado 80202

NOTICE OF SPECIAL MEETING OF COMMON UNITHOLDERS

To the common unitholders of Antero Midstream Partners LP:

        A special meeting (the "AM Special Meeting") of holders of common units ("AM Unitholders") of Antero Midstream Partners LP ("Antero Midstream") will be held on                                    ,                         at                         , local time, at 1615 Wynkoop Street, Denver, Colorado 80202, to consider and vote on a proposal to approve, (i) the Simplification Agreement, dated as of October 9, 2018, by and among Antero Midstream GP LP ("AMGP"), Antero Midstream and certain of their affiliates, as may be amended from time to time (the "Simplification Agreement"), (ii) the merger of an indirect, wholly owned subsidiary of Antero Midstream Corporation (an entity resulting from the conversion of AMGP to a Delaware corporation) ("New AM") with and into Antero Midstream (the "Merger"), as contemplated by the Simplification Agreement, with Antero Midstream surviving such Merger as an indirect, wholly owned subsidiary of New AM, and (iii) the other transactions contemplated by the Simplification Agreement (such transactions, the "Transactions" and such proposal, the "AM Merger Proposal").

        Approval of the AM Merger Proposal requires the affirmative vote of holders of both a majority of the outstanding common units representing limited partner interests in Antero Midstream (each, an "AM Common Unit") and a majority of the outstanding AM Common Units held by AM Unitholders other than Antero Midstream's general partner and its affiliates (the "Disinterested AM Unitholders"). We cannot complete the Merger unless the requisite AM Unitholders approve the AM Merger Proposal. Accordingly, your vote is very important regardless of the number of AM Common Units you own.

The board of directors of Antero Midstream's general partner (the "AM Board") and the conflicts committee of the AM Board (the "AM Conflicts Committee"), which consists of two members of the AM Board who satisfy the requirements to serve on a conflicts committee under the Antero Midstream partnership agreement, each has determined in good faith that the Transactions are in the best interests of Antero Midstream and the Disinterested AM Unitholders. The AM Conflicts Committee and the AM Board each recommends that the AM Unitholders vote FOR the AM Merger Proposal. For more information regarding the recommendation of the AM Conflicts Committee and the AM Board, see "Special Factors—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions."

        AM Unitholders should be aware that some of the directors and executive officers of Antero Midstream's general partner may have interests in the Transactions that are different from, or in addition to, the interests they may have as AM Unitholders. See "Special Factors—Interests of Certain Persons in the Transactions."

        Only AM Unitholders of record at the close of business on                                    ,                         are entitled to notice of and to vote at the AM Special Meeting. A list of AM Unitholders entitled to vote at the AM Special Meeting will be available for inspection at Antero Midstream's offices in Denver,

Colorado for any purpose relevant to the AM Special Meeting during normal business hours for a period of ten days before the meeting and at the AM Special Meeting. References to the AM Special Meeting in the enclosed joint proxy statement/prospectus are to the special meeting as may be adjourned or postponed.

YOUR VOTE IS IMPORTANT. REGARDLESS OF WHETHER YOU EXPECT TO ATTEND THE AM SPECIAL MEETING, PLEASE SUBMIT YOUR PROXY IN ONE OF THE FOLLOWING WAYS:

•

If you hold your AM Common Units in the name of a bank, broker or other nominee, you should follow the instructions provided by your bank, broker or other nominee when voting your AM Common Units.

•

If you hold your AM Common Units in your own name, you may submit your proxy by:

•

using the toll-free telephone number shown on the proxy card;

•

using the Internet website shown on the proxy card; or

•

marking, signing, dating and promptly returning the enclosed proxy card in the postage-paid envelope. It requires no postage if mailed in the United States.

        The enclosed joint proxy statement/prospectus provides a detailed description of the Merger and the Simplification Agreement. You are urged to read the joint proxy statement/prospectus, including any documents incorporated by reference, and the Annexes carefully and in their entirety. If you have any questions concerning the Merger or the enclosed joint proxy statement/prospectus, would like additional copies or need help voting your AM Common Units, please contact Antero Midstream's proxy solicitor:

MacKenzie Partners, Inc.
1407 Broadway—27th Floor
New York, New York 10018
Toll free: (800) 322-2885
Collect: (212) 929-5500
proxy@mackenziepartners.com

By order of the Board of Directors of
Antero Midstream Partners GP LLC,

Paul M. Rady
Chairman of the Board and Chief Executive Officer
Antero Midstream Partners GP LLC

IMPORTANT NOTE ABOUT THIS JOINT PROXY STATEMENT/PROSPECTUS

        This joint proxy statement/prospectus, which forms part of a registration statement on Form S-4 filed with the Securities and Exchange Commission (the "SEC"), constitutes a proxy statement of Antero Midstream under Section 14(a) of the Securities Exchange Act of 1934, as amended (the "Exchange Act"), with respect to the solicitation of proxies for the AM Special Meeting to, among other things, approve the AM Merger Proposal.

        This joint proxy statement/prospectus also constitutes a proxy statement of AMGP under Section 14(a) of the Exchange Act with respect to the solicitation of proxies for the AMGP Special Meeting to, among other things, approve the AMGP Proposals and the LTIP Proposal, and a prospectus of AMGP under Section 5 of the Securities Act, for shares of New AM Common Stock that will be issued to AMGP Shareholders in the Conversion or paid to AM Unitholders in the Merger, in each case pursuant to the Simplification Agreement.

        As permitted under the rules of the SEC, this joint proxy statement/prospectus incorporates by reference important business and financial information about AMGP and Antero Midstream from other documents filed with the SEC that are not included in or delivered with this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 270 of this joint proxy statement/prospectus. You can obtain any of the documents incorporated by reference into this document from AMGP or Antero Midstream, as the case may be, or from the SEC's website at http://www.sec.gov. This information is also available to you without charge upon your request in writing or by telephone from AMGP or Antero Midstream at the following addresses and telephone numbers:

Antero Midstream GP LP
Antero Midstream Partners LP
Attention: Investor Relations
1615 Wynkoop Street
Denver, Colorado 80202
Telephone: (303) 357-7310

        Please note that copies of the documents provided to you will not include exhibits, unless the exhibits are specifically incorporated by reference into the documents or this joint proxy statement/prospectus.

        You may obtain certain of these documents at AMGP's website, http://www.anteromidstreamgp.com, and at Antero Midstream's website, http://www.anteromidstream.com. Information contained on AMGP's and Antero Midstream's websites is expressly not incorporated by reference into this joint proxy statement/prospectus.

In order to receive timely delivery of requested documents in advance of the special meetings, your request should be received no later than                                    ,                         . If you request any documents, AMGP or Antero Midstream will mail them to you by first class mail, or another equally prompt means, after receipt of your request.

        AMGP and Antero Midstream have not authorized anyone to give any information or make any representation about the Transactions, AMGP or Antero Midstream that is different from, or in addition to, that contained in this joint proxy statement/prospectus or in any of the materials that have been incorporated by reference into this joint proxy statement/prospectus. Therefore, if anyone distributes this type of information, you should not rely on it. If you are in a jurisdiction where offers to exchange or sell, or solicitations of offers to exchange or purchase, the securities offered by this joint proxy statement/prospectus or the solicitation of proxies are unlawful, or you are a person to whom it is unlawful to direct these types of activities, then the offer presented in this joint proxy statement/prospectus does not extend to you. The information contained in this joint proxy statement/prospectus speaks only as of the date of this joint proxy statement/prospectus, or in the case of information in a document incorporated by reference, as of the date of such document, unless the information specifically indicates that another date applies. All information in this document concerning AMGP has been furnished by AMGP. All information in this document concerning Antero Midstream has been furnished by Antero Midstream.

JOINT PROXY STATEMENT/PROSPECTUS

TABLE OF CONTENTS

Defined Terms	iv
SUMMARY TERM SHEET	1
The Parties to the Transactions	1
Relationships of the Parties to the Transactions	2
Organizational Chart Before the Transactions	3
The Simplification Agreement Transactions	3
Organizational Chart After the Transactions	7
Interests of Certain Persons in the Transactions	7
Security Ownership of Certain Beneficial Owners and Management of AMGP and Antero Midstream	7
Directors and Executive Officers of New AM Following the Transactions	8
AMGP Special Meeting	8
AM Special Meeting	9
Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions	10
Opinion of the AMGP Conflicts Committee's Financial Advisor	11
Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions	11
Opinion of the AM Conflicts Committee's Financial Advisor	12
The Simplification Agreement	12
Other Information Related to the Merger	16
Summary of Risk Factors	17
Selected Historical Consolidated Financial Data of Antero Midstream	19
Selected Historical Consolidated Financial Data of AMGP	20
Unaudited Pro Forma Condensed Combined Financial Information	21
Unaudited Comparative Per Share/Unit Information	22
QUESTIONS AND ANSWERS ABOUT THE TRANSACTIONS AND THE SPECIAL MEETINGS	24
SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS	36
SPECIAL FACTORS	38
Effects of the Transactions	38
Background of the Transactions	39
Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions	76
Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions	82
Position of Antero Resources as to the Fairness of the Transactions	87
Position of the AMGP Parties, AM Parties, Management Holders and Sponsor Holders as to the Fairness of the Transactions	89
Projected Financial Information	90
Non-GAAP Financial Measures	94
Opinion of the AMGP Conflicts Committee's Financial Advisor	95
Opinion of the AM Conflicts Committee's Financial Advisor	108
Opinion of the AR Special Committee's Financial Advisor	126
J.P. Morgan Financial Advisor Materials Provided to Antero Resources	141
Morgan Stanley Financial Advisor Materials Provided to Antero Midstream	144

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Citigroup Global Markets Inc. Financial Advisor Discussion Materials Provided to the Sponsor Holders	147
Relationship of the Parties to the Transactions	151
Interests of Certain Persons in the Transactions	152
Security Ownership of Certain Beneficial Owners and Management of AMGP and Antero Midstream	157
Transactions in AMGP Common Shares and AM Common Units	160
No Appraisal Rights	160
Accounting Treatment of the Transactions	160
Estimated Fees and Expenses	161
Regulatory Approvals Required for the Merger	161
Directors and Executive Officers of New AM Following the Transactions	161
Stockholders' Agreement	164
AM Unitholders Making Elections	164
Proration and Adjustment Procedures	166
Listing of Shares of New AM Common Stock	167
Delisting and Deregistration of AM Common Units	167
Provisions for Unaffiliated Security Holders	168
Ownership of Antero Midstream After the Merger	168
Restrictions on Sales of New AM Common Stock Received in the Transactions	168
RISK FACTORS	169
Risks Related to the Transactions	169
Risk Factors Relating to the Ownership of New AM Common Stock	175
Tax Risks Related to the Merger and the Ownership of New AM Common Stock Received in the Merger	179
THE PARTIES TO THE TRANSACTIONS	182
Antero Midstream and AMP GP	182
AMGP, AMGP GP and IDR Holdings	182
Antero Resources	182
Preferred Co, NewCo and Merger Sub	182
THE AMGP SPECIAL MEETING	183
General Information About the AMGP Special Meeting	183
Proxy Submission Procedures	184
THE AM SPECIAL MEETING	187
General Information About the AM Special Meeting	187
Proxy Submission Procedures	188
THE AMGP PROPOSALS AND THE AM MERGER PROPOSAL: THE SIMPLIFICATION AGREEMENT AND THE TRANSACTIONS	191
Structure of the Merger	191
When the Merger Becomes Effective	194
Effect of Merger on Outstanding AM Common Units and Other Interests	194
Exchange of Certificates; No Fractional Units	196
Actions Pending the Merger	199
Conditions to the Merger	200
Representations and Warranties	202
Covenants	202
Termination	209
Costs and Expenses	210
Effect of Termination	210
No Third Party Beneficiaries	210
Modification or Amendment and Waiver of Conditions	211

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Specific Performance	211
Governing Law	212
Other Important Agreements Related to the Transactions	212
DESCRIPTION OF THE DEBT FINANCING FOR THE MERGER	216
Overview	216
COMPARISON OF THE RIGHTS OF NEW AM STOCKHOLDERS, AMGP SHAREHOLDERS AND AM UNITHOLDERS	217
DESCRIPTION OF CAPITAL STOCK	237
Authorized Capital Stock of New AM	237
Common Stock	237
Preferred Stock	237
Provisions of New AM's Certificate of Incorporation and Bylaws	239
Transfer Agent and Registrar	242
Listing	242
NEW AM LONG TERM INCENTIVE PLAN PROPOSAL	243
Background and Purpose of the Proposal	243
Summary of the New AM LTIP	245
Eligibility to Participate	245
Securities to be Offered	245
Administration	246
Source of Shares	246
Awards Under the New AM LTIP	246
Other Provisions	248
Federal Income Tax Consequences	249
Tax Consequences to Participants under the New AM LTIP	249
Tax Consequences to New AM	252
New Plan Benefits	252
Securities Authorized for Issuance Under Equity Compensation Plans	252
Consequences of Failing to Approve the Proposal	253
Vote Required	253
MATERIAL U.S. FEDERAL INCOME TAX CONSEQUENCES	254
Tax Consequences of the Merger to U.S. Holders of AM Common Units	255
Tax Consequences to U.S. Holders of Owning and Disposing of New AM Common Stock Received in the Merger	257
Information Reporting and Backup Withholding	258
UNAUDITED PRO FORMA CONDENSED COMBINED FINANCIAL STATEMENTS	259
AM UNITHOLDER PROPOSALS	267
AMGP SHAREHOLDER PROPOSALS	268
OTHER MATTERS	269
LEGAL MATTERS	270
EXPERTS	270
WHERE YOU CAN FIND MORE INFORMATION	270
ANNEXES
Annex A—Simplification Agreement
Annex B—Fairness Opinion of the AM Conflicts Committee's Financial Advisor
Annex C—Fairness Opinion of the AMGP Conflicts Committee's Financial Advisor
Annex D—Fairness Opinion of the AR Special Committee's Financial Advisor
Annex E—Form of Certificate of Incorporation of New AM
Annex F—Form of Bylaws of New AM
Annex G—Form of Long-Term Incentive Plan of New AM

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Defined Terms

        The following frequently-used terms have the meanings set forth below for purposes of this joint proxy statement/prospectus, unless the context otherwise indicates:

•

"AM Board" means the board of directors of AMP GP.

•

"AM Common Units" means the common units representing limited partner interests in Antero Midstream.

•

"AM Conflicts Committee" means the conflicts committee of the AM Board.

•

"AM LTIP" means the Antero Midstream Partners LP Long-Term Incentive Plan.

•

"AM Merger Proposal" means the proposal to approve the Merger, the Simplification Agreement and the other transactions contemplated by the Simplification Agreement, to be considered for a vote of the AM Unitholders and a separate vote of the Disinterested AM Unitholders at the AM Special Meeting.

•

"AM Parties" means Antero Midstream and AMP GP.

•

"AM Public Unitholders" means AM Unitholders, excluding Antero Resources.

•

"AM Special Meeting" means the special meeting of AM Unitholders to be held on                        ,            .

•

"AM Unitholder Approval" means the approval of the AM Merger Proposal by holders of a majority of the outstanding AM Common Units and by holders of a majority of the outstanding AM Common Units held by the Disinterested AM Unitholders.

•

"AM Unitholders" means all holders of AM Common Units.

•

"AMGP" means Antero Midstream GP LP, a Delaware limited partnership.

•

"AMGP Board" means the board of directors of AMGP GP.

•

"AMGP Common Shares" means the common shares representing limited partner interests in AMGP.

•

"AMGP Conflicts Committee" means the conflicts committee of the AMGP Board.

•

"AMGP GP" means AMGP GP LLC, a Delaware limited liability company and the general partner of AMGP.

•

"AMGP GP Sponsors" means the members of AMGP GP, including certain funds affiliated with Warburg Pincus LLC, certain funds affiliated with Yorktown Partners LLC, Paul M. Rady and Glen C. Warren, Jr.

•

"AMGP LTIP" means the Antero Midstream GP LP Long-Term Incentive Plan (as amended, restated, modified or supplemented from time to time).

•

"AMGP Parties" means AMGP GP, AMGP, IDR Holdings, Preferred Co, NewCo and Merger Sub.

•

"AMGP Partnership Agreement" means the Agreement of Limited Partnership of AMGP, dated as of May 9, 2017, as amended by Amendment No. 1, dated as of October 9, 2018.

•

"AMGP Proposals" means (i) the Conversion Proposal, (ii) the AMGP Transaction Proposal, and (iii) the Issuance Proposal.

•

"AMGP Shareholder Approval" means the approval of (i) the Conversion Proposal by holders of a majority of the AMGP Common Shares, (ii) the AMGP Transaction Proposal by Disinterested

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AMGP Shareholder Approval and (iii) the Issuance Proposal by a majority of the votes cast on such proposal at the AMGP Special Meeting.

•

"AMGP Shareholders" means all holders of AMGP Common Shares.

•

"AMGP Special Meeting" means the special meeting of the AMGP Shareholders to be held on                        ,                         .

•

"AMGP Transaction Proposal" means the proposal to approve the Merger, the Simplification Agreement and the other transactions contemplated in the Simplification Agreement, including the Series B Exchange, to be considered for a vote of the requisite AMGP Shareholders at the AMGP Special Meeting.

•

"AMGP Voting Agreement" means the voting agreement between Antero Midstream and the AMGP Shareholders party thereto.

•

"AMGP VWAP" the average of the 20-day volume weighted average price per AMGP Common Share prior to the Election Deadline.

•

"AMP GP" means Antero Midstream Partners GP LLC, a Delaware limited liability company and the general partner of Antero Midstream.

•

"Antero Management" means the members of management of each of Antero Resources, AMGP GP and AMP GP, as applicable.

•

"Antero Midstream" means Antero Midstream Partners LP, a Delaware limited partnership, and its subsidiaries collectively or, if the context requires, Antero Midstream Partners LP individually.

•

"Antero Midstream Partnership Agreement" means the Agreement of Limited Partnership of Antero Midstream, dated as of November 10, 2014, as amended by Amendment No. 1, dated as of February 23, 2016, and Amendment No. 2, dated as of December 20, 2017.

•

"Antero Resources" means Antero Resources Corporation, a Delaware corporation and the holder of a majority of the outstanding AM Common Units, and its subsidiaries collectively or, if the context requires, Antero Resources Corporation individually.

•

"AR Board" means the board of directors of Antero Resources Corporation.

•

"AR Special Committee" means the special committee of the AR Board.

•

"AR Voting Agreement" means the voting agreement between AMGP and Antero Resources.

•

"Baird" means Robert W. Baird & Co. Incorporated, as financial advisor to the AR Special Committee.

•

"Code" means the Internal Revenue Code of 1986, as amended.

•

"Conversion" means the conversion of AMGP into a Delaware corporation to be named Antero Midstream Corporation (referred in this joint proxy statement/prospectus as "New AM") in accordance with the Plan of Conversion as set forth in the Simplification Agreement.

•

"Conversion Proposal" means the proposal to approve the Conversion, including a certificate of conversion and certificate of incorporation, the AMGP Shareholders will be asked to vote on.

•

"Disinterested AM Unitholder Approval" means the approval by a vote of holders of a majority of the outstanding AM Common Units held by the Disinterested AM Unitholders.

•

"Disinterested AM Unitholders" means the AM Unitholders other than AMP GP or its affiliates, which affiliates include (i) Antero Resources, (ii) the Sponsor Holders, (iii) the

v

Management Holders and all other Series B Holders, (iv) the respective controlled affiliates of the persons described in the foregoing clauses (i)-(iii) and (v) any other affiliates of AMP GP identified by the AM Conflicts Committee that own AM Common Units as of the record date for the AM Special Meeting.

•

"Disinterested AMGP Shareholder Approval" means the approval by a vote of holders of a majority of the AMGP Common Shares held by the Disinterested AMGP Shareholders.

•

"Disinterested AMGP Shareholders" means the AMGP Shareholders other than AMGP GP or its affiliates, which affiliates include (i) the Sponsor Holders, (ii) the Management Holders and all other Series B Holders, (iii) the respective controlled affiliates of the Persons described in the foregoing clauses (i)-(ii) and (iv) any other affiliates of AMGP GP identified by the AMGP Conflicts Committee that own AMGP Common Shares as of the record date for the AMGP Special Meeting.

•

"Election Deadline" means, with respect to an AM Public Unitholder's election to receive Public Mixed Consideration, Public Stock Consideration or Public Cash Consideration (each as defined in this joint proxy statement/prospectus), the date by which such AM Public Unitholder must make such election with respect to such holder's AM Common Units. The Election Deadline will be 5:00 p.m., New York City time, on the later of the twentieth day following the mailing of the form of election and ten days prior to the anticipated closing date of the Transactions, or such other time as mutually agreed by AMGP and Antero Midstream.

•

"Exchange Act" means the Securities Exchange Act of 1934, as amended.

•

"Goldman Sachs" means Goldman Sachs & Co. LLC, as financial advisor to the AMGP Conflicts Committee.

•

"GP Merger" means the merger of AMP GP with and into AMGP, whereby AMGP will continue as the surviving entity and the separate existence of AMP GP will cease, which merger will, at the election of AMP GP, be completed prior to the Conversion.

•

"IDR Holdings" means Antero IDR Holdings LLC, a Delaware limited liability company and the holder of the incentive distribution rights in Antero Midstream.

•

"IDR Holdings LLC Agreement" means the limited liability company agreement of IDR Holdings, dated as of December 31, 2016, as amended by Amendment No. 1 thereto, dated as of May 9, 2018, and as amended by Amendment No. 2 thereto, dated as of October 9, 2018.

•

"Issuance Proposal" means the proposal to approve the issuance of New AM Common Stock pursuant to the Simplification Agreement.

•

"J.P. Morgan" means J.P. Morgan Securities LLC, financial advisor to Antero Resources.

•

"LTIP Proposal" means the proposal to approve the adoption of the New AM LTIP.

•

"Management Holders" means (i) Paul M. Rady, Mockingbird Investments LLC and each other entity, trust or estate planning vehicle over which Paul M. Rady controls or is deemed to have both voting and dispositive power and (ii) Glen C. Warren, Jr., Canton Investment Holdings LLC and each other entity, trust or estate planning vehicle over which Glen C. Warren, Jr. controls or is deemed to have both voting and dispositive power.

•

"Merger" means, as contemplated by the Simplification Agreement, the proposed merger of Merger Sub with and into Antero Midstream, with Antero Midstream surviving the Merger as an indirect, wholly owned subsidiary of New AM, and each AM Common Unit outstanding at the effective time of the Merger being converted into the right to receive the applicable Merger Consideration.

vi

•

"Merger Consideration" means, if the proposed Merger is consummated, (i) the right of each AM Public Unitholder to receive, in exchange for each AM Common Unit held by such holder, at the election of such holder and subject to proration, one of (A) the Public Mixed Consideration, (B) the Public Stock Consideration or (C) the Public Cash Consideration (each as defined herein) and (ii) the right of Antero Resources to receive, in exchange for each AM Common Unit held by it, the AR Mixed Consideration (as defined herein). Antero Resources will be able to elect to take a larger portion of the AR Mixed Consideration in cash if the AM Public Unitholders elect to receive less in cash consideration than the amount of Public Available Cash (as defined herein).

•

"Merger Sub" means Arkrose Midstream Merger Sub LLC, a Delaware limited liability company and wholly owned subsidiary of NewCo.

•

"Morgan Stanley" means Morgan Stanley & Co. LLC, financial advisor to Antero Midstream.

•

"New AM" means Antero Midstream Corporation, a Delaware corporation that will result from the Conversion.

•

"New AM Board" means the board of directors of New AM.

•

"New AM Common Stock" means the common stock of New AM, par value $0.01.

•

"New AM LTIP" means the proposed Long-Term Incentive Plan of Antero Midstream Corporation.

•

"New AM Stockholders" means the holders of New AM Common Stock.

•

"NewCo" means Arkrose Midstream NewCo Inc., a Delaware corporation and wholly owned subsidiary of AMGP.

•

"NYSE" means the New York Stock Exchange.

•

"Preferred Co" means Arkrose Midstream Preferred Co LLC, a Delaware limited liability company and wholly owned subsidiary of AMGP.

•

"SEC" means the United States Securities and Exchange Commission.

•

"Securities Act" means the Securities Act of 1933, as amended.

•

"Series A Units" means the Series A Units representing limited liability company interests in IDR Holdings.

•

"Series B Exchange Shares" means the shares of New AM Common Stock transferred in exchange for outstanding Series B Units pursuant to the Series B Exchange.

•

"Series B Holders" means the holders of the Series B Units, solely in their capacity as such.

•

"Series B Units" means the Series B Units representing limited liability company interests in IDR Holdings.

•

"Simplification Agreement" means that certain Simplification Agreement, dated as of October 9, 2018, by and among AMGP, AMGP GP, Antero Midstream, AMP GP, NewCo, Preferred Co and Merger Sub, as it may be amended from time to time, according to which the parties thereto have agreed to consummate the Transactions.

•

"Sponsor Holders" (i) Warburg Pincus Private Equity VIII, L.P., a Delaware limited partnership, Warburg Pincus Netherlands Private Equity VIII C.V. I, a company formed under the laws of the Netherlands, WP-WPVIII Investors, L.P., a Delaware limited partnership, Warburg Pincus Private Equity X O&G, L.P., a Delaware limited partnership, Warburg Pincus X Partners, L.P., a Delaware limited partnership, WP-WPVIII Investors GP L.P., a Delaware limited partnership,

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Warburg Pincus X, L.P., a Delaware limited partnership, Warburg Pincus X GP L.P., a Delaware limited partnership, WPP GP LLC, a Delaware limited liability company, Warburg Pincus Partners, L.P., a Delaware limited partnership, Warburg Pincus Partners GP LLC, a Delaware limited liability company, Warburg Pincus & Co., a New York general partnership, Warburg Pincus LLC, a New York limited liability company, and Charles R. Kaye and Joseph P. Landy, who are the Managing General Partners of Warburg Pincus & Co. and Managing Members and Co-Chief Executive Officers of Warburg Pincus LLC and (ii) Yorktown Energy Partners V, L.P., Yorktown Energy Partners VI, L.P., Yorktown Energy Partners VII, L.P. and Yorktown Energy Partners VIII, L.P.

•

"Transactions" means the transactions contemplated by the Simplification Agreement, including the GP Merger, the Conversion, the Merger, the Series B Exchange and the issuance of New AM Common Stock.

•

"Tudor Pickering" means Tudor Pickering Holt & Co Advisors LP, as financial advisor to the AM Conflicts Committee.

viii

SUMMARY TERM SHEET

The following summary, together with the section entitled "Questions and Answers about the Transactions and the Special Meetings," highlights some of the information in this joint proxy statement/prospectus. It may not contain all of the information that is important to you. To understand the Transactions fully, and for a more complete description of the terms of the Simplification Agreement, you should read carefully this joint proxy statement/prospectus, the documents incorporated by reference and the Annexes to this joint proxy statement/prospectus, including the full text of the Simplification Agreement included as Annex A. Please also read "Where You Can Find More Information" on page 270 of this joint proxy statement/prospectus. Where appropriate, we have set forth a section and page reference directing you to a more complete description of the topics described in this summary.

The Parties to the Transactions

Antero Midstream and AMP GP

        Antero Midstream is a Delaware limited partnership formed by Antero Resources to own, operate and develop midstream energy assets to service Antero Resources' rapidly increasing production. Its assets consist of gathering pipelines, compressor stations, processing and fractionation plants and water handling and treatment assets, through which it provides midstream services to Antero Resources primarily under long-term, fixed-fee and cost-plus contracts. AM Common Units trade on the NYSE under the symbol "AM." Antero Midstream is managed by its general partner, AMP GP.

AMGP, AMGP GP and IDR Holdings

        AMGP is a Delaware limited partnership whose sole assets are (i) 100% of the limited liability company interests in AMP GP, resulting in indirect ownership of the general partner interest in Antero Midstream, and (ii) 100% of the Series A Units of, and a managing member interest in, IDR Holdings. The AMGP Common Shares trade on the NYSE under the symbol "AMGP." AMGP is managed by its general partner, AMGP GP. Certain funds affiliated with Warburg Pincus LLC, certain funds affiliated with Yorktown Partners LLC, Paul M. Rady and Glen C. Warren, Jr. collectively own 100% of the limited liability company interests in AMGP GP.

        IDR Holdings is a Delaware limited liability company that owns all of the incentive distribution rights in Antero Midstream, which entitle their holders to receive cash distributions from Antero Midstream when distributions exceed certain target amounts. AMGP serves as the managing member of IDR Holdings and holds all of the Series A Units, while certain members of Antero Management own all of the Series B Units in IDR Holdings. AMGP's only source of income is distributions made by IDR Holdings on the Series A Units, and IDR Holdings' only source of income is distributions made by Antero Midstream on the incentive distribution rights.

Antero Resources

        Antero Resources is a Delaware corporation with its common stock traded on the NYSE under the symbol "AR." Antero Resources and its subsidiaries are engaged in the exploration, development, production, and acquisition of natural gas, natural gas liquids, and oil properties located in the Appalachian Basin. Antero Resources owns 53% of the outstanding AM Common Units.

Preferred Co, NewCo and Merger Sub

        Preferred Co is a Delaware limited liability company, NewCo is a Delaware corporation and Merger Sub is a Delaware limited liability company. Each of Preferred Co and NewCo are wholly owned subsidiaries of AMGP, and Merger Sub is a wholly owned subsidiary of NewCo. Each of

1

Preferred Co, NewCo and Merger Sub were formed or incorporated in contemplation of the Transactions.

        For more information regarding the parties to the Transactions, see "The Parties to the Transactions" beginning on page 182 of this joint proxy statement/prospectus.

Relationships of the Parties to the Transactions

        The parties to the Transactions are closely related. The most material relationships are:

•

Significant Board Overlap.  Four individuals, Paul M. Rady, Glen C. Warren, Jr., Peter R. Kagan and W. Howard Keenan, Jr., serve as members of each of the AM Board, the AMGP Board and the AR Board. James R. Levy serves as a member of both the AMGP Board and the AR Board. Richard W. Connor serves as a member of both the AR Board and the AM Board and as the chairman of their respective audit committees.

•

Significant Antero Management Overlap.  Mr. Rady is the Chairman and Chief Executive Officer of each of Antero Midstream, AMGP and Antero Resources. Mr. Warren is the President of Antero Midstream and AMGP and the President and Chief Financial Officer of Antero Resources. Michael N. Kennedy is a Senior Vice President and Chief Financial Officer of Antero Midstream and AMGP and a Senior Vice President of Antero Resources. Alvyn A. Schopp is the Chief Administrative Officer, Regional Senior Vice President and Treasurer of Antero Midstream, AMGP and Antero Resources. Kevin J. Kilstrom is a Senior Vice President of Antero Midstream, AMGP and Antero Resources. The remaining members of Antero Management have similar titles and responsibilities at each entity.

•

Sponsor Holder and Management Holder Ownership.

•

Certain funds affiliated with Warburg Pincus LLC currently own approximately 55.1 million AMGP Common Shares, or 29.6% of all outstanding AMGP Common Shares, and 33.6 million shares of Antero Resources common stock, or 10.6% of all outstanding shares of Antero Resources common stock. Certain funds affiliated with Warburg Pincus LLC also own a 40% limited liability company interest in AMGP GP.

•

Certain funds affiliated with Yorktown Partners LLC currently own approximately 15.5 million AMGP Common Shares, or 8.3% of all outstanding AMGP Common Shares, and 14.0 million shares of Antero Resources common stock, or 4.4% of all outstanding shares of Antero Resources common stock. Certain funds affiliated with Yorktown Partners LLC also own a 20% limited liability company interest in AMGP GP.

•

Mr. Rady owns approximately 20.0 million AMGP Common Shares, or 10.7% of all outstanding AMGP Common Shares, 194,152 AM Common Units, or less than 1% of all outstanding AM Common Units, and 14.9 million shares of Antero Resources common stock, or 4.7% of all shares of outstanding Antero Resources common stock. Mr. Rady also owns a 20% limited liability company interest in AMGP GP.

•

Mr. Warren owns approximately 14.9 million AMGP Common Shares, or 8.0% of all outstanding AMGP Common Shares, 134,996 AM Common Units, or less than 1% of all outstanding AM Common Units, and 10.9 million shares of Antero Resources common stock, or 3.4% of all shares of outstanding Antero Resources common stock. Mr. Warren also owns a 20% limited liability company interest in AMGP GP.

•

Mr. Rady and Mr. Warren also own approximately 49% and 32%, respectively, of all outstanding Series B Units in IDR Holdings. For additional information regarding the Series B Units and what will happen to them in connection with the Transactions, please see "Special Factors—Interests of Certain Persons in the Transactions."

2

•

Commercial Relationships.  Antero Midstream has long-term contractual arrangements with Antero Resources pursuant to which Antero Midstream provides gathering and compression services and water handling and treatment services to Antero Resources. Antero Midstream also owns a 50% interest in a joint venture with MarkWest Energy Partners, L.P. that provides gas processing and fractionation services to Antero Resources. Substantially all of Antero Midstream's revenues are currently derived from Antero Resources.

        For more information regarding these relationships and related party transactions between AMGP, Antero Midstream and Antero Resources, see "Special Factors—Relationship of the Parties to the Transactions" beginning on page 151 of this joint proxy statement/prospectus.

Organizational Chart Before the Transactions

        The following diagram summarizes the organizational structure of the Antero entities immediately prior to giving effect to the Transactions (based on ownership interests as of December 4, 2018).

(1)

An additional 18,600 Series B Units are currently held by certain members of Antero Management other than the Management Holders, which Series B Units are not depicted in the above diagram.

The Simplification Agreement Transactions

The Transactions (See page 39)

        On the closing date of the Transactions, the primary transactions will be completed in order as follows:

•

GP Merger—First, at AMP GP's option, prior to the Conversion, AMP GP will merge with and into AMGP, with AMGP continuing as the surviving entity and the separate existence of AMP GP ceasing (the "GP Merger").

3

•

The Conversion—Second, following the GP Merger (if any), AMGP will convert from a limited partnership to a corporation under the laws of the State of Delaware named "Antero Midstream Corporation." In the Conversion, each AMGP Shareholder will receive an equivalent number of shares of New AM Common Stock, a certificate of incorporation of New AM will be filed with the Delaware Secretary of State and the bylaws of New AM will become effective.

•

The Merger—Third, following the Conversion, Merger Sub will merge with and into Antero Midstream, with Antero Midstream surviving the merger as a wholly owned subsidiary of NewCo. In connection with the Merger, all of the AM Common Units outstanding as of the effective time of the Merger will be converted into the right to receive the Merger Consideration as described under "—The Merger Consideration" below.

•

The Series B Exchange—Concurrently with the Merger, all of the issued and outstanding Series B Units will be exchanged for an aggregate of approximately 17.35 million shares of New AM Common Stock (the "Series B Exchange"), as more fully described under "—Series B Exchange" below. A total of 98,600 Series B Units are currently outstanding.

        As a result of the Transactions, former AMGP Shareholders, AM Unitholders and Series B Holders will all own New AM Common Stock, Antero Midstream will be an indirect, wholly owned subsidiary of New AM and the AMGP Common Shares and AM Common Units will cease to trade on the NYSE. New AM Common Stock will trade on the NYSE under the symbol "AM." It is expected that the outstanding AMGP Common Shares, AM Common Units and Series B Units will be exchanged for approximately 37%, 60% and 3%, respectively, of the outstanding New AM Common Stock following completion of the Transactions, based upon the amount of outstanding equity at each entity as of December 4, 2018.

        For more information on the Transactions, please see "Special Factors—Effects of the Transactions" beginning on page 38 of this joint proxy statement/prospectus.

The Merger Consideration

        At the effective time of the Merger:

•

in exchange for each AM Common Unit held, each AM Public Unitholder will be entitled to receive, at its election and subject to proration, one of:

•

$3.415 in cash without interest and 1.6350 shares of New AM Common Stock (the "Public Mixed Consideration");

•

1.6350 shares of New AM Common Stock plus an additional number of shares of New AM Common Stock equal to the quotient of (A) $3.415 and (B) the AMGP VWAP (the "Public Stock Consideration"); or

•

$3.415 in cash plus an additional amount of cash, in each case without interest, equal to the product of (A) 1.6350 and (B) the AMGP VWAP (the "Public Cash Consideration"); and

•

in exchange for each AM Common Unit held, Antero Resources will be entitled to receive, subject to certain adjustments (as described below), $3.00 in cash without interest and 1.6023 shares of New AM Common Stock (the "AR Mixed Consideration").

        The aggregate cash consideration to be paid as Merger Consideration will be fixed at an amount equal to the aggregate amount of cash that would be paid if all AM Public Unitholders received the Public Mixed Consideration (the "Public Available Cash") and Antero Resources received the AR Mixed Consideration (collectively, the "Available Cash Consideration"), which is approximately $598 million in the aggregate. However, if the Public Available Cash exceeds the cash consideration elected to be received by the AM Public Unitholders (the amount of such excess, "Excess Available

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Cash"), Antero Resources may elect to increase the total amount of cash it receives as a part of the AR Mixed Consideration up to an amount equal to the Excess Available Cash. To the extent Antero Resources elects to receive additional cash, the number of shares it receives will be reduced accordingly based on the AMGP VWAP. In addition, the Merger Consideration each AM Public Unitholder will receive may be prorated in the event that more cash or equity is elected to be received than what would otherwise have been paid if all AM Public Unitholders received the Public Mixed Consideration and Antero Resources received the AR Mixed Consideration.

Treatment of Series B Units and Equity Awards

        Antero Midstream previously issued phantom units to its executive officers and other service providers under the AM LTIP, and IDR Holdings previously issued Series B Units to certain members of Antero Management under the IDR Holdings LLC Agreement. At the effective time of the Merger, all awards of Antero Midstream phantom units that are outstanding immediately prior to the effective time of the Merger, whether vested or unvested, will be assumed by New AM and converted into restricted stock units or similar awards settled in New AM Common Stock based on a formula that utilizes the exchange rates of the Public Mixed Consideration. This assumption and conversion will occur irrespective of whether the LTIP Proposal is approved by AMGP Shareholders. For a discussion of what will happen to the Series B Units, see "Series B Exchange" below. For a more complete discussion of the treatment of Antero Midstream equity awards, see "Special Factors—Interests of Certain Persons in the Transactions—Treatment of Series B Units and Equity Awards Held by Antero Midstream Executives" beginning on page 152 of this joint proxy statement/prospectus.

Series B Exchange

        Pursuant to the Simplification Agreement, AMGP, as the managing member of IDR Holdings, and Mr. Rady and Mr. Warren, as the holders of a majority of the Series B Units, entered into an amendment to the IDR Holdings LLC Agreement (the "IDR Holdings LLCA Amendment") to facilitate the Series B Exchange. Prior to amending the IDR Holdings LLC Agreement, the Series B Holders were entitled to receive in the aggregate up to 6% of all quarterly cash distributions in excess of $7.5 million distributed by Antero Midstream on its incentive distribution rights and had the ability to cause the redemption of vested Series B Units for AMGP Common Shares with a value equal to such holder's pro rata share of up to 6% of AMGP's market capitalization at the time of redemption (calculated by reference to the 20-day volume weighted average price of the AMGP Common Shares preceding the date of redemption request) in excess of $2.0 billion. Pursuant to the IDR Holdings LLCA Amendment, the Series B Holders agreed to exchange each outstanding Series B Unit for 176.0041 shares of New AM Common Stock. A total of 98,600 Series B Units are currently outstanding. Based on the number of outstanding AM Common Units and AMGP Common Shares and their respective closing sales prices as of October 8, 2018 (the last trading day before the day the Simplification Agreement was announced), the approximately 17.35 million shares of New AM Common Stock expected to be transferred in the Series B Exchange represent approximately 4.4% of the pro forma market capitalization of New AM in excess of $2 billion (representing approximately 3.4% of the total pro forma market capitalization of New AM). The number of shares of New AM Common Stock to be transferred in exchange for outstanding Series B Units will be reduced proportionately if a holder forfeits his or her Series B Units prior to closing, with no re-allocation to the remaining holders.

        The Series B Exchange Shares will be subject to the same vesting conditions to which the Series B Units are currently subject, with one-third fully vested, one-third scheduled to vest at December 31, 2018 and one-third scheduled to vest at December 31, 2019. Distributions declared but not yet paid with respect to vested Series B Units will be delivered in connection with the Series B Exchange. Consistent with the existing terms of the Series B Units, distributions declared on unvested Series B

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Units prior to the closing date of the Transactions will not be paid until the applicable vesting date of the Series B Exchange Shares. At the time of the Transactions, cash in an amount equal to these unpaid distributions will be deposited into an escrow account to be released at the time of vesting, excluding any amounts attributable to any distributions made with respect to unvested Series B Units after December 31, 2018 but prior to the effective time of the Merger. With respect to the Series B Units and Series B Exchange Shares scheduled to vest on December 31, 2019, the Series B Holders have agreed to forgo any distributions from IDR Holdings and any dividends from New AM that are paid with respect to such units or shares, as applicable, during the twelve months ending December 31, 2019.

Other Ancillary Transactions

        In connection with the Simplification Agreement, the parties will enter into certain other transactions, including:

•

Antero Midstream will amend its partnership agreement to, among other things, facilitate the GP Merger;

•

New AM will contribute up to $120.00 (and in no event less than $100.00) of cash to Preferred Co and will issue up to 12,000 shares (and in no event less than 10,000 shares) of Series A Non-Voting Perpetual Preferred Stock, par value $0.01, of New AM (the "New AM Preferred Stock"), to Preferred Co for consideration of $0.01 per share; and

•

Preferred Co will transfer such New AM Preferred Stock to The Antero Foundation, a charitable organization, for no consideration (together, with the preceding bullet point, the "Preferred Stock Issuance").

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Organizational Chart After the Transactions

        The following diagram summarizes the organizational structure of Antero entities immediately after giving effect to the Merger and the Transactions (based on ownership interests as of December 4, 2018).

Interests of Certain Persons in the Transactions

        AM Unitholders and AMGP Shareholders should be aware that each of the executive officers and certain of the directors of AMP GP and AMGP GP have interests in the Transactions that may differ from, or may be in addition to, the interests of AM Unitholders and AMGP Shareholders generally. As described under "Special Factors—Relationships of the Parties to the Transactions" above, each of the executive officers of Antero Midstream and AMGP and certain of the directors of Antero Midstream and AMGP serve as directors and/or executive officers of other entities party to the Transactions, and many of those individuals also own equity interests in more than one entity involved in the Transactions, meaning those persons' economic interests may not be aligned with those of AM Unitholders or AMGP Shareholders.

        For more detail about these interests, see "Special Factors—Relationships of the Parties to the Transactions" and "Special Factors—Interests of Certain Persons in the Transactions" beginning on page 151 and 152 of this joint proxy statement/prospectus, respectively.

Security Ownership of Certain Beneficial Owners and Management of AMGP and Antero Midstream

Ownership of AMGP Common Shares by Directors and Executive Officers of AMGP GP

        As of                        ,             , all of the directors, executive officers and affiliates of AMGP GP beneficially owned, in the aggregate            AMGP Common Shares, representing approximately        

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% of the outstanding AMGP Common Shares. Pursuant to the AMGP Voting Agreement, the shareholder parties thereto that collectively beneficially own approximately 57% of the AMGP Common Shares outstanding (the "AMGP Voting Agreement Shareholders") have agreed to vote in favor of each of the AMGP Proposals. The parties to the AMGP Voting Agreement are not Disinterested AMGP Shareholders, so their votes will not affect the outcome of the AMGP Transaction Proposal. AMGP believes that all of the remaining directors and executive officers of AMGP GP will also vote in favor of each of the AMGP Proposals.

Ownership of AM Common Units by Directors and Executive Officers of AMP GP and of Antero Resources in Antero Midstream

        As of                        ,             , all of the directors and executive officers of AMP GP beneficially owned, in the aggregate,             AM Common Units, representing less than 1% of the outstanding AM Common Units, and Antero Resources owned 98,870,335 AM Common Units, representing approximately 53% of the outstanding AM Common Units. Pursuant to the AR Voting Agreement, Antero Resources has agreed to vote (or cause to be voted) all of the AM Common Units it owns in favor of the AM Merger Proposal. Antero Midstream believes that all of the directors and executive officers of AMP GP will vote in favor of the AM Merger Proposal.

        See "Special Factors—Security Ownership of Certain Beneficial Owners and Management of AMGP and Antero Midstream" beginning on page 157 of this joint proxy statement/prospectus.

Directors and Executive Officers of New AM Following the Transactions

        All of the executive officers of AMP GP are currently also executive officers of AMGP GP. Following the Transactions, these individuals will continue as executive officers of New AM.

        Upon completion of the Transactions, nearly all members of each board will continue as members of the New AM Board, and the New AM Board will be classified. The initial members of the New AM Board will be: (i) W. Howard Keenan, Jr., Peter A. Dea, and David A. Peters (the "Class I Directors"), (ii) Glen C. Warren, Jr., Brooks J. Klimley, and John C. Mollenkopf (the "Class II Directors") and (iii) Peter R. Kagan, Paul M. Rady, and Rose M. Robeson (the "Class III Directors"). Mr. Rady will be the Chairman of the New AM Board. The Class I Directors' terms will expire at the first annual meeting following the closing of the Transactions, the Class II Directors' terms will expire at the second annual meeting following the closing of the Transactions, and the Class III Directors' terms will expire at the third annual meeting following the closing of the Transactions.

        Pursuant to the Stockholders' Agreement, a majority of the New AM Board will at all times consist of directors who are independent under the listing rules of the NYSE and the Exchange Act and who are unaffiliated with Antero Resources, the Sponsor Holders and the Management Holders. These independent and unaffiliated directors will be nominated for election to the New AM Board by the Nominating and Governance Committee of the New AM Board (the "Nominating and Governance Committee"), which will itself consist solely of independent and unaffiliated directors.

        For more information regarding the New AM Board and the Stockholders' Agreement, see "Special Factors—Directors and Executive Officers of New AM Following the Transactions" and "Special Factors—Stockholders' Agreement" on pages 161 and 164, respectively, of this joint proxy statement/prospectus.

AMGP Special Meeting

Where and When

        Where and when:    The AMGP Special Meeting will take place at 1615 Wynkoop Street, Denver, Colorado 80202, on                        ,        at             , local time.

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What You Are Being Asked to Vote On

        At the AMGP Special Meeting, AMGP Shareholders will vote on the Conversion Proposal, the AMGP Transaction Proposal, the Issuance Proposal and the LTIP Proposal. AMGP Shareholders may also be asked to consider other matters as may properly come before the AMGP Special Meeting. At this time, AMGP knows of no other matters that will be presented for the consideration of the AMGP Shareholders at the AMGP Special Meeting.

Who May Vote

        You may vote at the AMGP Special Meeting if you owned AMGP Common Shares at the close of business on the record date of                        ,                 . On that date, there were                        AMGP Common Shares outstanding. You may cast one vote for each outstanding AMGP Common Share that you owned as of the record date.

What Constitutes a Quorum

        The presence, in person or by proxy, at the AMGP Special Meeting of the holders of a majority of issued and outstanding AMGP Common Shares as of the record date will constitute a quorum and will permit AMGP to conduct the proposed business at the AMGP Special Meeting. AMGP Common Shares held in your name will count as present at the AMGP Special Meeting if you (i) are present in person at the AMGP Special Meeting or (ii) have submitted and not revoked a properly executed proxy card or properly submitted your proxy by telephone or internet. Proxies received but marked abstentions will be counted as AMGP Common Shares that are present and entitled to vote for purposes of determining the presence of a quorum. Broker non-votes will also be considered present at the AMGP Special Meeting for purposes of determining the presence of a quorum.

What Vote Is Needed

        Approval of the Conversion Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares, and approval of the AMGP Transaction Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares held by the Disinterested AMGP Shareholders. Each of the LTIP Proposal and the Issuance Proposal requires the affirmative vote of holders of a majority of the AMGP Common Shares voted on such proposals at the AMGP Special Meeting.

        Completion of the Transactions is not conditioned upon approval of the LTIP Proposal. Even if the AMGP Shareholders approve the LTIP Proposal, AMGP will not adopt the New AM LTIP unless the Transactions are completed.

AM Special Meeting

Where and When

        Where and when:    The AM Special Meeting will take place at 1615 Wynkoop Street, Denver, Colorado 80202, on                        ,        at             , local time.

What You Are Being Asked to Vote On

        At the AM Special Meeting, the AM Unitholders will vote on the AM Merger Proposal. AM Unitholders may also be asked to consider other matters as may properly come before the AM Special Meeting. At this time, Antero Midstream knows of no other matters that will be presented for the consideration of the AM Unitholders at the AM Special Meeting.

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Who May Vote

        You may vote at the AM Special Meeting if you owned AM Common Units at the close of business on the record date of                        ,         at            . On that date, there were                        AM Common Units. You may cast one vote for each outstanding AM Common Unit that you owned as of the record date.

What Constitutes a Quorum

        The presence, in person or by proxy, at the AM Special Meeting of the holders of a majority of issued and outstanding AM Common Units as of the record date will constitute a quorum and will permit Antero Midstream to conduct the proposed business at the AM Special Meeting. AM Common Units held in your name will count as present at the AM Special Meeting if you (i) are present in person at the AM Special Meeting or (ii) have submitted and not revoked a properly executed proxy card or properly submitted your proxy by telephone or internet. Proxies received but marked abstentions will be counted as AM Common Units that are present and entitled to vote for purposes of determining the presence of a quorum. Broker non-votes will not be considered present at the AM Special Meeting for purposes of determining the presence of a quorum.

What Vote Is Needed

        Approval of the AM Merger Proposal requires the affirmative vote of holders of a majority of the outstanding AM Common Units and the affirmative vote of holders of a majority of the outstanding AM Common Units held by the Disinterested AM Unitholders.

Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions

        On October 8, 2018, the AMGP Conflicts Committee unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, (iii) recommended to the AMGP Board that the AMGP Board approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, and submit the AMGP Proposals to a vote of the AMGP Shareholders and (iv) recommended to the Disinterested AMGP Shareholders that the Disinterested AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents. The AMGP Conflicts Committee's approval constitutes "Special Approval," as such term is defined in the AMGP Partnership Agreement.

        Later on October 8, 2018, upon receiving the recommendation of the AMGP Conflicts Committee and a report of, among other things, its reasons for recommending approval of the Transactions, the AMGP Board unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents and (iii) recommended to the AMGP Shareholders that the AMGP Shareholders approve the Transactions, including the Merger and the issuance or

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payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents.

        The AMGP Conflicts Committee consulted with its financial and legal advisors and considered many factors in making its determination, approvals and recommendation. For a discussion of the factors, see "Special Factors—Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions" beginning on page 76 of this joint proxy statement/prospectus.

Opinion of the AMGP Conflicts Committee's Financial Advisor

        Goldman Sachs rendered to the AMGP Conflicts Committee its oral opinion, which was subsequently confirmed by delivery of a written opinion, dated October 9, 2018, that, as of the date of such written opinion and based upon and subject to the factors and assumptions set forth therein, after giving effect to the issuance of shares of New AM Common Stock pursuant to the Series B Exchange, the Aggregate Consideration (as defined in such opinion) to be paid by AMGP for the AM Common Units pursuant to the Simplification Agreement was fair from a financial point of view to AMGP.

The full text of the written opinion of Goldman Sachs, dated October 9, 2018, which sets forth assumptions made, procedures followed, matters considered and limitations on the review undertaken in connection with the opinion, is attached hereto as Annex C. Goldman Sachs provided advisory services and its opinion for the information and assistance of the AMGP Conflicts Committee in connection with its consideration of the Transactions. The Goldman Sachs opinion is not a recommendation as to how any holder of AMGP Common Shares should vote with respect to the Transactions or any other matter. Pursuant to an engagement letter between the AMGP Conflicts Committee and Goldman Sachs, AMGP has agreed to pay Goldman Sachs a transaction fee of $4,000,000, $2,000,000 of which became payable upon the execution of the engagement letter, and the remainder of which is contingent upon consummation of the Transactions. Goldman Sachs may receive an additional fee at the AMGP Conflict Committee's sole discretion.

Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions

        On October 8, 2018, the AM Conflicts Committee unanimously (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AM and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, (iii) recommended to the AM Board that the AM Board approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, and submit the AM Merger Proposal to a vote of the AM Unitholders and (iv) recommended to the Disinterested AM Unitholders that the Disinterested AM Unitholders approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents. The AM Conflicts Committee's approval constitutes "Special Approval," as such term is defined in the Antero Midstream Partnership Agreement.

        Later on October 8, 2018, upon receiving the recommendation of the AM Conflicts Committee and a report of, among other things, its reasons for recommending approval of the Transactions, the AM Board unanimously (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AM and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents and (iii) recommended to the AM Unitholders that the AM Unitholders approve the

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Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents.

        The AM Conflicts Committee consulted with its financial and legal advisors and considered many factors in making its determination, approvals and recommendation. For a discussion of the factors, see "Special Factors—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions" beginning on page 82 of this joint proxy statement/prospectus.

Opinion of the AM Conflicts Committee's Financial Advisor

        At the request of the AM Conflicts Committee at a meeting of the AM Conflicts Committee held on October 8, 2018, Tudor Pickering rendered its oral opinion to the AM Conflicts Committee that, as of October 8, 2018, based upon and subject to the assumptions, qualifications, limitations and other matters considered relevant by Tudor Pickering in connection with the preparation of its opinion, the Merger Consideration to be received by the Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement was fair, from a financial point of view, to the Disinterested AM Unitholders. Tudor Pickering subsequently confirmed its oral opinion in writing dated October 8, 2018 to the AM Conflicts Committee.

Tudor Pickering's opinion was directed to the AM Conflicts Committee (in its capacity as such), and only addressed the fairness, from a financial point of view, as of the date of the opinion, to the Disinterested AM Unitholders of the Merger Consideration to be received by the Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement. Tudor Pickering's opinion did not address any other term or aspect of the Simplification Agreement or the Transactions. The full text of Tudor Pickering's written opinion, dated October 8, 2018, which describes the assumptions made, procedures followed, matters considered, and qualifications and limitations of the review undertaken by Tudor Pickering in rendering its opinion, is attached as Annex B to this joint proxy statement/prospectus. The summary of Tudor Pickering's opinion set forth in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the opinion. AM Unitholders are urged to read Tudor Pickering's opinion carefully and in its entirety. However, neither Tudor Pickering's written opinion nor the summary of its opinion and the related analyses set forth in this joint proxy statement/prospectus are intended to be, and they do not constitute, a recommendation as to how the AM Conflicts Committee or the AM Board, AMP GP or any other person should act or vote with respect to any matter relating to the Merger, the other Transactions or any other matter. Pursuant to the terms of its engagement, upon preparation and delivery of Tudor Pickering's opinion to the AM Conflicts Committee (regardless of the conclusion reached therein), Tudor Pickering became entitled to receive fees of $1.5 million (not including any retainer fees, which fees shall not exceed $1,000,000), which will be credited against the transaction fee of $3.0 million payable to Tudor Pickering upon the consummation of the Transactions.

The Simplification Agreement

        The Simplification Agreement is attached to this joint proxy statement/prospectus as Annex A and is incorporated by reference. You are encouraged to read the Simplification Agreement in its entirety because it is the legal document that governs the Transactions.

Conditions to Completion of the Transactions

        AMGP and Antero Midstream currently expect to complete the Transactions shortly following the conclusion of the AMGP Special Meeting and the AM Special Meeting, subject to receipt of AMGP Shareholder Approval and AM Unitholder Approval, regulatory approvals and clearances and the

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satisfaction or waiver of other conditions to the Transactions contemplated by the Simplification Agreement described below.

        As more fully described in this joint proxy statement/prospectus and in the Simplification Agreement, each party's obligation to complete the Transactions depends on a number of conditions being satisfied or, where legally permissible, waived, including the following:

•

the registration statement of which this joint proxy statement/prospectus is a part must have become effective under the Securities Act, this joint proxy statement/prospectus must have been mailed to all AM Unitholders and AMGP Shareholders 20 business days prior to the closing of the Transactions, and no stop order suspending the effectiveness of the registration statement has been issued and no proceedings for that purpose may have been initiated or threatened by the SEC unless subsequently withdrawn;

•

the AMGP Shareholder Approval and the AM Unitholder Approval have been obtained;

•

no court or other governmental entity of competent jurisdiction will have enacted, issued, promulgated, enforced or entered any permanent, preliminary or temporary injunction or other order, decree, decision, determination or judgment that would delay, restrain, prevent, enjoin or otherwise prohibit consummation of the Transactions contemplated by the Simplification Agreement;

•

any waiting period applicable to the Transactions under the Hart-Scott-Rodino Antitrust Act of 1976, as amended, (the "HSR Act") must have been terminated or expired (the Antitrust Division and the FTC (each as defined below) granted early termination of the applicable waiting period under the HSR Act on November 19, 2018); and

•

the shares of New AM Common Stock to be paid in the Merger and the Series B Exchange must have been approved for listing on the NYSE, subject to official notice of issuance.

        The obligations of the AMGP Parties and the AM Parties to effect the Transactions are also subject to the satisfaction or waiver of the following conditions:

•

the representations and warranties of the other parties being true and correct both at and as of the date of the Simplification Agreement and as of the closing of the Transactions, subject to certain standards, including materiality and material adverse effect qualifications, as described under "The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions—Conditions to the Merger" beginning on page 200 of this joint proxy statement/prospectus;

•

each and all of the agreements and covenants of the other parties to be performed and complied with pursuant to the Simplification Agreement on or prior to the closing of the Transactions must have been duly performed and complied with in all material respects; and

•

the receipt, at the closing of the Transactions, of a certificate signed by an executive officer of the other parties and to the effect that the conditions described in the first two bullet points immediately above have been satisfied.

Changes in Recommendation

AMGP Change in Recommendation

        The AMGP Conflicts Committee and the AMGP Board have recommended approval of the AMGP Proposals (the "AMGP Conflicts Committee Recommendation" and the "AMGP Board Recommendation," respectively). At any time prior to obtaining the AMGP Shareholder Approval, the AMGP Conflicts Committee or AMGP Board may withdraw, modify or qualify in any manner adverse to the AM Parties or any other party the AMGP Conflicts Committee Recommendation or the AMGP

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Board Recommendation, as applicable (any such action an "AMGP Change in Recommendation"), if the AMGP Conflicts Committee or AMGP Board, as applicable, concludes in good faith, after consultation with its outside legal advisors and its financial advisors, if any, that the Transactions are no longer in the best interests of the Disinterested AMGP Shareholders. AMGP must provide to Antero Midstream five business days' prior written notice advising Antero Midstream that the AMGP Conflicts Committee or AMGP Board, as applicable, intends to change its recommendation and specifying the reasons for the change in recommendation in reasonable detail. Any AMGP Change in Recommendation will not change the AMGP Conflicts Committee's or the AMGP Board's approval of the Simplification Agreement (including, with respect to the AMGP Conflicts Committee, the granting of "Special Approval" as defined in the AMGP Partnership Agreement) and the Transactions or any other approval of the AMGP Board.

AM Change in Recommendation

        The AM Conflicts Committee and the AM Board have recommended approval of the AM Merger Proposal (the "AM Conflicts Committee Recommendation" and the "AM Board Recommendation," respectively). At any time prior to obtaining the AM Unitholder Approval, the AM Conflicts Committee or AM Board may withdraw, modify or qualify in any manner adverse to the AMGP Parties or any other party the AM Conflicts Committee Recommendation or the AM Board Recommendation, as applicable (any such action, an "AM Change in Recommendation"), if the AM Conflicts Committee or AM Board, as applicable, concludes in good faith, after consultation with its outside legal advisors and its financial advisors, if any, that the Transactions are no longer in the best interests of the Disinterested AM Unitholders. Antero Midstream must provide to AMGP five business days' prior written notice advising AMGP that the AM Conflicts Committee or AM Board, as applicable, intends to change its recommendation and specifying the reasons for the change in recommendation in reasonable detail. Any AM Change in Recommendation will not change the AM Conflicts Committee's or the AM Board's approval of the Simplification Agreement (including, with respect to the AM Conflicts Committee, the granting of "Special Approval" as defined in the Antero Midstream Partnership Agreement) and the Transactions or any other approval of the AM Board.

Termination of the Simplification Agreement

        The Simplification Agreement may be terminated at any time prior to the effective time of the Merger:

•

by mutual written consent of the AM Parties and the AMGP Parties.

•

by either AMGP Parties or the AM Parties, subject to certain limitations, if:

•

the Merger has not been consummated by April 30, 2019 (the "Termination Date");

•

there is any order, injunction or judgment or similar determination that has become final and non-appealable that prohibits the consummation of the Transactions;

•

the AMGP Shareholder Approval is not obtained;

•

the AM Unitholder Approval is not obtained; or

•

any of the Conversion, the Preferred Stock Issuance, the contribution of New AM Common Stock to NewCo for purposes of the Series B Exchange or the Series B Exchange is not consummated.

•

by the AM Parties if:

•

there is a breach of any representation, warranty, covenant or agreement of an AMGP Party by an AMGP Party, or any representation or warranty of such AMGP Party becomes untrue

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after the date of the Simplification Agreement, such breach would give rise to the failure of Antero Midstream's closing conditions under the Simplification Agreement, and such breach is not curable by the Termination Date; or

•

the AMGP Board or AMGP Conflicts Committee effects an AMGP Change in Recommendation prior to the AMGP Shareholder Approval being obtained.

•

by the AMGP Parties if:

•

there is a breach of any representation, warranty, covenant or agreement of an AM Party by an AM Party, or any representation or warranty of such AM Party becomes untrue after the date of the Simplification Agreement, such breach would give rise to the failure of AMGP's closing conditions under the Simplification Agreement, and such breach is not curable by the Termination Date; or

•

the AM Board or AM Conflicts Committee effects an AM Change in Recommendation prior to the time the AM Unitholder Approval being obtained.

Expenses Relating to the Merger

        Regardless of whether the Transactions are consummated, all costs and expenses incurred in connection with the Transactions will be paid by the party incurring such costs and expenses. However, AMGP paid the filing fees associated with the filing of the HSR Act Notification and Report Forms in connection with the Transactions, including the HSR Act Notification and Report Forms filed by the Management Holders in connection with the Transactions. Antero Midstream will reimburse AMGP for 50% of the filing fees associated with the filing of the HSR Act Notification and Report Forms.

        For more detail about the expenses relating to the Transactions, see "The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions" beginning on page 191 of this joint proxy statement/prospectus.

Financing of the Merger

        The cash portion of the Merger Consideration will be funded utilizing borrowings under Antero Midstream's revolving credit facility. On October 31, 2018, Antero Midstream amended its credit facility to, among other things, increase the borrowing capacity under the facility from $1.5 billion to $2.0 billon.

Material U.S. Federal Income Tax Consequences of the Merger (page 254)

        The Merger should be a taxable event for each AM Public Unitholder that is a U.S. holder (as defined in the section titled "Material U.S. Federal Income Tax Consequences"). The specific expected U.S. federal income tax consequences of the Merger to an AM Public Unitholder that is a U.S. holder are dependent upon whether such unitholder receives only Public Cash Consideration or also receives Public Stock Consideration.

        If a U.S. holder receives only Public Cash Consideration, the payment of the Public Cash Consideration should be treated for U.S. federal income tax purposes as a distribution from Antero Midstream to such U.S. holder in liquidation of such U.S. holder's interest in Antero Midstream that will only be taxable to the U.S. holder to the extent the amount of the distribution exceeds the U.S. holder's tax basis in its AM Common Units. Any gain or loss recognized will be treated as gain or loss from the taxable sale of AM Common Units.

        If a U.S. holder receives Public Stock Consideration and Public Cash Consideration and/or cash in lieu of fractional shares of New AM Common Stock, the payment of the cash amounts should be treated for U.S. federal income tax purposes as a current distribution to such U.S. holder from Antero Midstream. Such distribution will first reduce such U.S. holder's tax basis in its AM Common Units and will only be taxable to the U.S. holder to the extent the amount of the distribution exceeds the U.S. holder's tax basis in its AM Common Units. Any gain recognized will be treated as gain from the taxable sale of AM Common Units.

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        The receipt of the Public Stock Consideration by a U.S. holder should be treated for U.S. federal income tax purposes as a taxable sale of AM Common Units for New AM Common Stock, with such taxable sale being treated as occurring immediately after the current distribution described above. Such U.S. holder will recognize gain or loss in an amount equal to the difference between:

•

the sum of (i) the fair market value of any New AM Common Stock received and (ii) such U.S. holder's share of Antero Midstream's nonrecourse liabilities immediately prior to the Merger; and

•

such U.S. holder's adjusted tax basis in the AM Common Units exchanged therefor (which will include such U.S. holder's share of Antero Midstream's nonrecourse liabilities immediately prior to the Merger), as reduced (but not below zero) by any Public Cash Consideration and any cash in lieu of fractional shares of New AM Common Stock received by such U.S. holder.

        Gain or loss recognized by a U.S. holder in connection with the Merger will generally be capital gain or loss. However, a portion of such gain or loss, which portion could be substantial, will be separately computed and taxed as ordinary income or loss under Section 751 of the Code to the extent attributable to assets giving rise to depreciation recapture or other "unrealized receivables" or to "inventory items" owned by Antero Midstream and its subsidiaries. Passive losses that were not deductible by a U.S. holder in prior taxable periods because they exceeded a U.S. holder's share of Antero Midstream's income may become available to offset a portion of the gain recognized by such U.S. holder in connection with the Merger.

The U.S. federal income tax consequences of the Merger to an AM Public Unitholder will depend on such unitholder's own personal tax situation. Accordingly, each AM Unitholder is strongly urged to consult its own tax advisor for a full understanding of the particular tax consequences of the Merger to such unitholder.

        For additional information regarding the material U.S. federal income tax consequences of the Merger, read the section titled "Material U.S. Federal Income Tax Consequences." For additional information regarding the expected U.S. federal income tax consequences of the Conversion, read "Questions and Answers About the Transactions and the Special Meetings—What are the expected U.S. federal income tax consequences to an AMGP Shareholder that is a U.S. person (as defined in the Code) of the Conversion."

Other Information Related to the Merger

No Appraisal Rights

        AM Unitholders do not have appraisal rights under the Antero Midstream Partnership Agreement, the Simplification Agreement or Delaware or other applicable law. See "Special Factors—No Appraisal Rights" on page 160 of this joint proxy statement/prospectus.

Regulatory Approvals Required for the Merger

        Under the HSR Act and related rules, the Transactions may not be completed until the parties to the Transactions submit the required HSR Notification and Report Forms to the Antitrust Division of the United States Department of Justice, which is referred to as the "Antitrust Division," and the United States Federal Trade Commission, which is referred to as the "FTC," and all statutory waiting period requirements under the HSR Act have been satisfied. On November 5, 2018, each of AMGP, Antero Midstream, Antero Resources, Paul M. Rady and Glen C. Warren, Jr. filed HSR Act Notification and Report Forms, which are referred to as the "HSR Forms," with the Antitrust Division and the FTC. The Antitrust Division and the FTC granted early termination of the applicable waiting period under the HSR Act on November 19, 2018. However, at any time before or after completion of the Transactions, the Department of Justice (the "DOJ"), the FTC or any state may request additional

16

information or could take such action under the antitrust laws as it deems necessary or desirable in the public interest, including seeking to enjoin the completion of the Transactions, to rescind the Transactions or to seek divestiture of particular assets of AMGP or Antero Midstream. Private parties also may seek to take legal action under the antitrust laws under certain circumstances.

Delisting and Deregistration of AM Common Units and Listing of New AM Common Stock

        Upon completion of the Merger, AM Common Units currently listed on the NYSE will cease to be listed on the NYSE and will be subsequently deregistered under the Exchange Act.

        The New AM Common Stock issued or paid in connection with the Transactions will be listed on the NYSE under the symbol "AM."

Provisions for Unaffiliated Security Holders

        No provision has been made to grant AMGP Shareholders or AM Unitholders access to the files of AMGP or Antero Midstream or to obtain counsel or appraisal services at the expense of AMGP or Antero Midstream.

Accounting Treatment

        AMGP is the sole member of AMP GP, the general partner of Antero Midstream, and also controls the incentive distribution rights in Antero Midstream through its ownership interest in IDR Holdings (subject to the rights of the Series B Holders to receive distributions in respect of their Series B Units). As a result of the Merger, Antero Midstream will become an indirect, wholly owned subsidiary of New AM, and the AM Unitholders will collectively own a majority of the outstanding New AM Common Stock. This will result in New AM acquiring the incentive distribution rights of Antero Midstream that are currently held by AMGP. Because of the nature and effect of the Merger, the Transactions are treated for accounting purposes like an equity transaction among entities under common control and the historic carrying values of the assets, liabilities and equity interests of the parties to the Transactions are carried forward.

Comparison of the Rights of New AM Stockholders and AM Unitholders

        AMGP Shareholders that will own New AM Common Stock following the Conversion, and AM Unitholders that will own New AM Common Stock following the completion of the Merger, will have rights as stockholders of New AM that will be different from their current rights as AMGP Shareholders and AM Unitholders, respectively. See "Comparison of the Rights of New AM Stockholders, AMGP Shareholders and AM Unitholders" beginning on page 217 of this joint proxy statement/prospectus.

Summary of Risk Factors

        You should consider carefully all of the risk factors together with all of the other information included in this joint proxy statement/prospectus before deciding how to vote. Risks relating to the Conversion, the Merger and ownership of New AM Common Stock are described in the section titled "Risk Factors." Some of the risks include, but are not limited to, those described below:

•

AM Unitholders who will receive New AM Common Stock as part of the Merger Consideration cannot be sure of the market value of the New AM Common Stock they will receive until the closing of the Transactions;

•

AM Unitholders may not receive the amount of cash consideration or stock consideration they elected to receive due to proration and adjustment, and therefore such unitholders may receive

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consideration having an aggregate value that is less than the aggregate value of the consideration they elected to receive;

•

if the Transactions are approved by the AMGP Shareholders and the AM Unitholders, the date that AM Unitholders will receive the Merger Consideration is dependent on the completion date of the Transactions, which is uncertain;

•

the fairness opinions rendered to the AMGP Conflicts Committee, the AM Conflicts Committee and the AR Special Committee by Goldman Sachs, Tudor Pickering and Baird, respectively, were necessarily based on economic, monetary, market and other conditions as in effect on, and financial forecasts and other information made available to Goldman Sachs, Tudor Pickering and Baird as of, the dates of the respective opinions. As a result, each opinion does not reflect changes in events or circumstances after the date of such opinion. None of the AMGP Conflicts Committee, the AM Conflicts Committee or the AR Special Committee has obtained or requested or expects to obtain or request an updated fairness opinion from Goldman Sachs, Tudor Pickering or Baird, respectively, reflecting changes in circumstances that may have occurred since the signing of the Simplification Agreement;

•

financial projections by AMGP and Antero Midstream may not prove to be reflective of actual future results;

•

the New AM Board will be classified and certain provisions of the Stockholders' Agreement may make it difficult for stockholders to change the composition of the New AM Board;

•

the Merger should be a taxable event for the AM Public Unitholders, and the resulting tax liability, if any, of an AM Public Unitholder will depend on such unitholder's particular situation. Additionally, the amount and character of any taxable gain or loss recognized by an AM Public Unitholder as a result of the Merger or of any income or gain allocated to an AM Public Unitholder with respect to the taxable year that includes the Merger could be different than anticipated, potentially resulting in a tax liability that is more than expected;

•

the U.S. federal income tax treatment to AM Public Unitholders with respect to owning and disposing of any shares of New AM Common Stock received in the Merger will be different than the U.S. federal income tax treatment to them with respect to owning and disposing of their AM Common Units;

•

New AM's future tax liability may be greater than expected if it does not generate deductions or net operating loss carryforwards sufficient to offset taxable income or if tax authorities challenge certain of its tax positions;

•

AMGP and Antero Midstream are subject to contractual interim operating restrictions while the proposed Transactions are pending, which could adversely affect each party's business and operations;

•

if an AM Unitholder properly makes an election before the Election Deadline, they will not be able to transfer their AM Common Units during the period between the Election Deadline and the consummation of the proposed Merger, and after the Election Deadline there may not be a liquid market for the AM Common Units;

•

AMGP and Antero Midstream will incur substantial transaction-related costs in connection with the Transactions, and if the Transactions do not occur, AMGP and Antero Midstream will not benefit from the expenses they have incurred in pursuit of the Transactions;

•

the use of cash and incurrence of indebtedness in connection with the financing of the Transactions may have an adverse impact on New AM's liquidity and New AM's flexibility in responding to other business opportunities, and may increase the risk of noncompliance with

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restrictive covenants and may increase New AM's vulnerability to adverse economic and industry conditions;

•

New AM will have increased levels and costs of indebtedness used to fund the Transactions including the cash portion of the Merger Consideration and increased cost of existing indebtedness due to the actions taken to consummate the Transactions;

•

New AM Stockholders may not receive the anticipated level of dividends under the anticipated dividend policy or any dividends at all;

•

the directors and officers of each of AMGP GP and AMP GP, respectively, have certain interests that are different from those of AMGP Shareholders and AM Unitholders generally;

•

each of the AMGP Partnership Agreement and Antero Midstream Partnership Agreement limits the duties of each of AMGP GP and AMP GP to AMGP Shareholders and AM Unitholders, respectively, and restricts the remedies available to AMGP Shareholders and AM Unitholders, respectively, for actions taken by AMGP GP and AMP GP, respectively, that might otherwise constitute breaches of its duties;

•

AMGP and Antero Midstream may be subject to class action lawsuits relating to the Transactions, which could materially adversely affect their business, financial condition and operating results;

•

failure to complete, or significant delays in completing, the Transactions could negatively affect the trading prices of AMGP Common Shares and AM Common Units and the future business and financial results of AMGP and Antero Midstream;

•

the unaudited pro forma financial statements included in this joint proxy statement/prospectus are presented for illustrative purposes only and may not be an indication of the combined entity's financial condition or results of operations following the Transactions;

•

upon receiving New AM Common Stock as a result of the Transactions AM Unitholders and AMGP Shareholders will have different rights than the rights they currently have as holders of AM Common Units and AMGP Common Shares, respectively;

•

the price of New AM Common Stock may be volatile, and New AM Stockholders could lose a significant portion of their investments;

•

there may be future dilution of New AM Common Stock, which could adversely affect the market price of shares of New AM Common Stock;

•

sales of a substantial amount of shares of New AM Common Stock in the public market could adversely affect the market price of shares of New AM Common Stock; and

•

the New AM bylaws elect not to be subject to the provisions of Section 203 of the General Corporation Law of the State of Delaware (the "DGCL"), regulating corporate takeovers.

Selected Historical Consolidated Financial Data of Antero Midstream

        The following selected historical consolidated financial data as of and for each of the five years in the period ended December 31, 2017 are derived from Antero Midstream's audited consolidated financial statements. The selected historical consolidated financial data as of and for each of the nine month periods ended September 30, 2018 and 2017 are derived from Antero Midstream's unaudited condensed consolidated financial statements. You should read the following data in conjunction with "Management's Discussion and Analysis of Financial Condition and Results of Operations" and the consolidated financial statements and the related notes thereto set forth in Antero Midstream's Annual Report on Form 10-K for the year ended December 31, 2017 and Antero Midstream's Quarterly

19

Report on Form 10-Q for the quarterly period ended September 30, 2018 incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 270 of this joint proxy statement/prospectus.

	Year ended December 31,															Nine months ended September 30,
	2013			2014			2015			2016			2017			2017			2018
	($ in thousands, except per unit amounts)
Statement of operations data:
Revenues	$	58,234		$	266,274		$	387,324		$	590,211		$	772,497		$	562,165		$	746,771
Operating income		2,179			134,058			167,263			258,111			324,678			257,435			352,416
Net income and comprehensive income		2,015			127,875			159,105			236,703			307,315			243,160			337,335
Pre-IPO net income attributed to parent		(2,015	)		(98,219	)		—			—			—			—			—
Pre-Water Acquisition net income attributed to parent		—			(22,234	)		(40,193	)		—			—			—			—
Net income attributable to incentive distribution rights		—			—			(1,264	)		(16,944	)		(69,720	)		(45,948	)		(99,414	)
Limited partners' interest in net income	$	—		$	7,422		$	117,648		$	219,759		$	237,595		$	197,212		$	237,921
Net income per limited partner unit—basic and diluted	$	—		$	0.05		$	0.74		$	1.24		$	1.28		$	1.06		$	1.27
Distributions declared per unit	$	—		$	0.18		$	0.80		$	1.03		$	1.33		$	0.96		$	1.25
Weighted average limited partner units outstanding—basic		—			151,882			158,479			176,647			185,630			185,240			186,999
Weighted average limited partner units outstanding—diluted		—			151,882			158,527			176,801			186,083			185,728			187,342
Balance sheet data (at period end):
Cash and cash equivalents	$	—		$	230,192		$	6,883		$	14,042		$	8,363		$	2,495		$	—
Property and equipment, net		793,330			1,531,595			1,893,826			2,195,879			2,605,602			2,508,204			2,873,874
Total assets		808,337			1,816,610			1,980,032			2,349,895			3,042,209			2,895,391			3,414,828
Long-term indebtedness		—			115,000			620,000			849,914			1,196,000			1,067,722			1,516,854
Total capital		732,061			1,620,903			1,082,745			1,222,810			1,516,469			1,534,386			1,564,562

Selected Historical Consolidated Financial Data of AMGP

        The following selected historical consolidated financial data as of and for the period ended December 31, 2017 are derived from AMGP's audited consolidated financial statements. The selected historical consolidated financial data as of and for each of the nine month periods ended September 30, 2018 and 2017 are derived from AMGP's unaudited condensed consolidated financial statements. You should read the following data in conjunction with "Management's Discussion and Analysis of Financial Condition and Results of Operations" and the consolidated financial statements and the related notes thereto set forth in AMGP's Annual Report on Form 10-K for the year ended December 31, 2017 and AMGP's Quarterly Report on Form 10-Q for the quarterly period ended

20

September 30, 2018 incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 270 of this joint proxy statement/prospectus.

	Year Ended December 31,						Nine Months Ended September 30,
	2015		2016		2017		2017			2018
	(in thousands, except per share amounts)
Statement of operations data:
Total income	$	1,264	$	16,944	$	69,720	$	45,948		$	99,414
Net income and comprehensive income		781		9,711		2,325		(3,582	)		45,220
Net income per common share—basic and diluted	$	—	$	—	$	0.03	$	0.01		$	0.23
Distributions declared per share	$	—	$	—	$	0.16	$	0.09		$	0.38
Weighted average number of common shares outstanding—basic		—		—		186,176		186,172			186,199
Weighted average number of common shares outstanding—diluted		—		—		186,176		191,191			186,199
Balance sheet data (at period end):
Cash and cash equivalents	$	72	$	9,609	$	5,987	$	2,419		$	4,246
Total assets		1,041		17,369		29,759		21,535			42,258
Total capital		558		10,269		15,608		8,680			25,126

Unaudited Pro Forma Condensed Combined Financial Information

        The following table sets forth selected unaudited pro forma condensed combined financial information for New AM after giving effect to the Transactions. The selected unaudited pro forma condensed combined financial information is derived from the unaudited pro forma condensed combined financial statements included in this joint proxy statement/prospectus. For a complete discussion of the pro forma adjustments underlying the amounts in the table below, please read the

21

section titled "Unaudited Pro Forma Condensed Combined Financial Statements" beginning on page 259 of this joint proxy statement/prospectus.

	Year Ended December 31, 2017		Nine Months Ended September 30, 2018
	(in thousands, except per share amounts)
Income and Cash Flow Data:
Revenues	$	772,497	$	746,771
Operating income		283,544		326,443
Equity in earnings of unconsolidated affiliates		—		27,832
New AM Common Stock:
Total basic earnings per common share		0.28		0.43
Total diluted earnings per common share		0.28		0.42
Basic weighted-average number of shares outstanding New AM Common Stock		500,365		500,365
Diluted weighted-average number of shares outstanding New AM Common Stock		506,150		506,150
Dividends per common share declared for the period	$	0.69	$	0.80
Balance Sheet Data (at end of period):
Property, plant and equipment, net			$	2,873,874
Total assets				4,511,271
Long-term debt				2,114,583

Unaudited Comparative Per Share/Unit Information

        The following table sets forth: (a) certain historical per share information of AMGP; (b) certain historical per unit information of Antero Midstream; and (c) unaudited pro forma combined and equivalent pro forma combined per share information of New AM after giving effect to the Transactions.

	Year Ended December 31, 2017			Nine Months Ended September 30, 2018
Historical—AMGP
Net income per common share (basic and diluted)	$	0.03		$	0.23
Distributions per share declared for the period		0.16			0.38
Book value per share		(0.11	)		(0.05	)
Historical—Antero Midstream
Net income per limited partner unit (basic and diluted)	$	1.28		$	1.27
Distributions per unit declared for the period		0.69			0.80
Book value per unit		7.99			8.16
Pro forma combined—New AM
Net income per share (basic and diluted)	$	0.28		$	0.42
Distributions per share declared for the period		0.69			0.80
Book value per share					4.01
Equivalent pro forma combined
Net income per limited partner unit (basic and diluted)	$	0.52		$	0.77
Distributions per unit declared for the period		1.27			1.46
Book value per unit					7.38

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        AMGP Common Shares trade on the NYSE under the ticker symbol "AMGP," and AM Common Units trade on the NYSE under the ticker symbol "AM."

        The following table presents per share or unit closing prices for AMGP Common Shares and AM Common Units on October 8, 2018, the last trading day before AMGP announced its proposal to acquire all of the AM Common Units owned by the public, and on                ,                 , the last practicable trading day before the date of this joint proxy statement/prospectus. This table also presents the equivalent market value per AM Common Unit on such dates. The equivalent market value per AM Common Unit has been determined by multiplying the closing prices of the AMGP Common Shares on those dates by (i) an assumed exchange ratio of 1.6350 AMGP Common Shares, plus $3.415 in cash, for each outstanding AM Common Unit held by the AM Public Unitholders, and (ii) an assumed exchange ratio of 1.6023 AMGP Common Shares, plus $3.00 in cash, for each outstanding AM Common Unit held by the Antero Resources, in each case as if each AM Public Unitholder had elected to receive the Public Mixed Consideration in the Merger.

					Equivalent Market Value per AM Common Unit
	AMGP Common Shares		AM Common Units		AM Public Unitholders		Antero Resources
October 8, 2018	$	17.12	$	29.48	$	31.41	$	30.43
,	$		$		$		$

The market prices of the AMGP Common Shares and AM Common Units will fluctuate prior to the consummation of the Transactions, and the market value of the Merger Consideration ultimately received by AM Unitholders who will receive New AM Common Stock as part of the Merger Consideration will depend on the closing price of New AM Common Stock on the day the Transactions are consummated. As such, AM Unitholders will not know the exact market value of the Merger Consideration they will receive until the closing of the Transactions.

        As of                ,              the record date for the AMGP Special Meeting, AMGP had approximately              holders of record and              AMGP Common Shares outstanding. As of                ,              the record date for the AM Special Meeting, Antero Midstream had approximately              holders of record and              AM Common Units outstanding or issuable pursuant to outstanding Antero Midstream equity awards. Prior to the consummation of the Transactions, Antero Midstream generally expects to make cash distributions to AM Unitholders of record on the applicable record date within 60 days after the end of each quarter, and AMGP generally expects to make cash distributions to AMGP Shareholders promptly after receiving distributions in respect of its Series A Units in IDR Holdings. Aggregate distributions paid by Antero Midstream will be made from operating surplus to the extent Antero Midstream has sufficient cash after establishment of cash reserves and payment of fees and expenses, including payments to AMP GP and its affiliates.

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QUESTIONS AND ANSWERS ABOUT THE TRANSACTIONS AND THE SPECIAL MEETINGS

Important Information and Risks. The following are brief answers to some questions that you may have regarding the proposed Transactions, the AMGP Special Meeting and the AM Special Meeting. You should read and consider carefully the remainder of this joint proxy statement/prospectus, including the Risk Factors beginning on page 168 and the attached Annexes, because the information in this section does not provide all of the information that might be important to you. Additional important information and descriptions of risk factors are also contained in the documents incorporated by reference in this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 270 of this joint proxy statement/prospectus.

Q:    What is the proposed transaction and why am I receiving these materials?

A:

AMGP and Antero Midstream have agreed to a transaction by which (i) AMGP will convert from a Delaware limited partnership to a Delaware corporation named "Antero Midstream Corporation" that we refer to as "New AM," (ii) New AM and Antero Midstream will combine by merging an indirect, wholly owned subsidiary of New AM with and into Antero Midstream, with Antero Midstream surviving the Merger as an indirect, wholly owned subsidiary of New AM, and (iii) all of the issued and outstanding Series B Units of IDR Holdings, the holder of all of Antero Midstream's incentive distribution rights, will be exchanged for an aggregate of approximately 17.35 million shares of New AM Common Stock. The terms of the Simplification Agreement are described in this joint proxy statement/prospectus, and a copy of the Simplification Agreement is attached as Annex A. You are receiving these materials because the Transactions cannot be completed without certain approvals of the AMGP Shareholders and the AM Unitholders. You should carefully read this joint proxy statement/prospectus in its entirety, including any documents incorporated by reference, and the Annexes, before voting on any of the proposals.

Q:    Why are AMGP and Antero Midstream proposing the Transactions?

A:

AMGP and Antero Midstream believe that the Transactions will benefit both AMGP Shareholders and AM Unitholders for various reasons. For a discussion of those reasons, please see "Special Factors—Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions" and "Special Factors—Recommendation of the AM Conflicts Committee and the AM Board and their Reasons for Recommending Approval of the Transactions."

Q:    What will AMGP Shareholders receive in the Conversion?

A:

If the Conversion is completed, each AMGP Shareholder will receive one share of New AM Common Stock for each AMGP Common Share held. The number of shares of New AM Common Stock is fixed and will not be adjusted on account of any change in price of the AMGP Common Shares prior to completion of the Conversion. It is expected that the New AM Common Stock received in the Conversion by former holders of AMGP Common Shares will represent approximately 36.6% of the outstanding New AM Common Stock following completion of the Transactions.

Q:    What are the expected U.S. federal income tax consequences to an AMGP Shareholder that is a U.S. person (as defined in the Code) of the Conversion?

A.

Prior to the Conversion, AMGP is a Delaware limited partnership that has elected to be treated as a corporation for U.S. federal income tax purposes. Pursuant to the Conversion AMGP will convert from a Delaware limited partnership to a Delaware corporation, and following the Conversion AMGP will continue to be treated as the same corporation for U.S. federal income tax

24

purposes. As such, a holder of AMGP Common Shares that is a U.S. person (generally defined in the Code to include the categories of beneficial owners set forth in the definition of "U.S. holder" included in the section titled "Material U.S. Federal Income Tax Consequences") will be treated as owning stock in the same corporation for U.S. federal income tax purposes both before and after the Conversion and should not recognize gain or loss for U.S. federal income tax purposes as a result of the Conversion.

Q:    What will AM Unitholders receive in the Merger?

A:

If the Merger is completed, in exchange for each AM Common Unit held, each AM Public Unitholder will be entitled to receive, at its election and subject to proration, one of (i) the Public Mixed Consideration, (ii) the Public Stock Consideration, or (iii) the Public Cash Consideration. In exchange for each AM Common Unit held, Antero Resources will be entitled to receive, subject to certain adjustments, the AR Mixed Consideration. Based on the closing price of AMGP Common Shares on                        ,                         , the most recent trading day prior to the date of this joint proxy statement/prospectus, the aggregate value of the Merger Consideration was approximately $             billion. It is expected that the New AM Common Stock received in the Merger by former holders of AM Common Units will represent approximately            % of the outstanding New AM Common Stock following completion of the Transactions.

Q:    What are the expected U.S. federal income tax consequences to an AM Public Unitholder that is a U.S. holder (as defined in the section titled "Material U.S. Federal Income Tax Consequences") of the Merger?

A.

The Merger should be a taxable event for each AM Public Unitholder that is a U.S. holder. The specific expected U.S. federal income tax consequences of the Merger to an AM Public Unitholder that is a U.S. holder are dependent upon whether such holder receives only Public Cash Consideration or also receives Public Stock Consideration.

U.S. Holders Who Receive Only Public Cash Consideration

If a U.S. holder receives only Public Cash Consideration, the payment of the Public Cash Consideration should be treated for U.S. federal income tax purposes as a distribution from Antero Midstream to such U.S. holder in liquidation of such U.S. holder's interest in Antero Midstream that will only be taxable to the U.S. holder to the extent the amount of the distribution exceeds the U.S. holder's tax basis in its AM Common Units. The character of any such recognized gain or loss is described below.

U.S. Holders Who Receive Public Stock Consideration

If a U.S. holder receives Public Stock Consideration and Public Cash Consideration and/or cash in lieu of fractional shares of New AM Common Stock, the payment of the cash amounts should be treated for U.S. federal income tax purposes as a current distribution to such U.S. holder from Antero Midstream that will only be taxable to the U.S. holder to the extent the amount of the distribution exceeds the U.S. holder's tax basis in its AM Common Units.

The receipt of the Public Stock Consideration by a U.S. holder should be treated for U.S. federal income tax purposes as a taxable sale of AM Common Units for New AM Common Stock, with such taxable sale being treated as occurring immediately after the current distribution described above. Such U.S. holder will recognize gain or loss in an amount equal to the difference between (i) the sum of (A) the fair market value of any New AM Common Stock received and (B) such U.S. holder's share of Antero Midstream's nonrecourse liabilities immediately prior to the Merger and (ii) such U.S. holder's adjusted tax basis in the AM Common Units exchanged therefor (which

25

will include such U.S. holder's share of Antero Midstream's nonrecourse liabilities immediately prior to the Merger), as reduced (but not below zero) by any Public Cash Consideration and any cash in lieu of fractional shares of New AM Common Stock received by such U.S. holder.

Gain or loss recognized by a U.S. holder in connection with the receipt of Merger Consideration will generally be capital gain or loss. However, a portion of such gain or loss, which portion could be substantial, will be separately computed and taxed as ordinary income or loss to the extent attributable to assets giving rise to depreciation recapture or other "unrealized receivables" or to "inventory items" owned by Antero Midstream and its subsidiaries. Passive losses that were not deductible by a U.S. holder in prior taxable periods because they exceeded the U.S. holder's share of Antero Midstream's income may become available to offset a portion of any gain recognized by such U.S. holder in connection with the receipt of Merger Consideration.

See the section titled "Material U.S. Federal Income Tax Consequences" for a more complete discussion of certain U.S. federal income tax consequences of the Merger.

Q:    What will happen to the Series B Units in connection with the Transactions?

A:

If the Transactions are completed, each issued and outstanding Series B Unit will be exchanged for 176.0041 shares of New AM Common Stock for each Series B Unit, or an aggregate of approximately 17.35 million shares of New AM Common Stock. A total of 98,600 Series B Units are currently outstanding. The Series B Exchange Shares will be subject to the same vesting conditions to which the Series B Units are currently subject, with one-third fully vested, one-third scheduled to vest at December 31, 2018 and one-third scheduled to vest at December 31, 2019. Distributions declared but not yet paid with respect to vested Series B Units will be delivered in connection with the Series B Exchange. Consistent with the existing terms of the Series B Units, distributions declared on unvested Series B Units prior to the closing of the Transactions will not be paid until the applicable vesting date of the Series B Exchange Shares. At the time of the Transactions, cash in an amount equal to these unpaid distributions will be deposited into an escrow account to be released at the time of vesting, excluding any amounts attributable to any distributions made with respect to unvested Series B Units after December 31, 2018 but prior to the effective time of the Merger. With respect to Series B Units and Series B Exchange Shares scheduled to vest on December 31, 2019, the Series B Holders have agreed to forgo any distributions from IDR Holdings and any dividends from New AM that are paid with respect to such units or shares, as applicable, during the twelve months ending December 31, 2019. Based on the number of outstanding AM Common Units and AMGP Common Shares and their respective closing sales prices as of October 8, 2018 (the last trading day before the day the Simplification Agreement was announced), it is expected that the Series B Exchange Shares will represent approximately 4.4% of the pro forma market capitalization of New AM in excess of $2 billion (representing approximately 3.4% of the total pro forma market capitalization of New AM).

All of the Series B Units are held by certain members of Antero Management. For more detail about the interests of the executive officers and directors of AMGP GP and AMP GP in the Transactions, see "Special Factors—Interests of Certain Persons in the Transactions" beginning on page 152 of this joint proxy statement/prospectus.

Q:    What will happen to AM phantom units in the Transactions?

A:

At the effective time of the Merger, each award of Antero Midstream phantom units granted pursuant to the AM LTIP (as defined below) that remains outstanding immediately prior to the effective time of the Merger, whether vested or unvested, will be converted into a restricted stock unit or similar award of New AM, with substantially the same terms and conditions (including with respect to vesting) applicable to such AM Phantom Unit Award (as defined below) immediately

26

prior to the effective time of the Merger. For more information on the treatment of AM phantom units, see "Special Factors—The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions—Treatment of Series B Units and Equity Awards Held by Antero Midstream Executives."

Q:    Where will my shares or units trade after the completion of the Transactions?

A:

New AM Common Stock will trade on the NYSE under the symbol "AM." AM Common Units will no longer be publicly traded after the completion of the Transactions.

Q:    What happens to my future distributions or dividends?

A:

If the date of the closing of the Transactions is after the record date set by the AMGP Board in connection with declared distributions to be paid by AMGP to AMGP Shareholders, then a former AM Unitholder will not receive dividends for that quarter on the New AM Common Stock it receives in the Transactions, but will receive distributions for that quarter declared by Antero Midstream prior to the closing of the Transactions, if such former AM Unitholder was a record holder of such AM Common Units as of the record date with respect to such distribution. AM Unitholders will not receive both distributions from Antero Midstream and dividends from New AM for the same quarter. See "The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions—Dividends or Distributions."

Current AMGP Shareholders will continue to receive dividends on the New AM Common Stock they receive in the Conversion at the discretion of the New AM Board. See "The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions—Dividends or Distributions."

Under the anticipated dividend policy of New AM, subject to applicable law, AM Public Unitholders and AMGP Shareholders are expected to receive larger aggregate annual distributions on the New AM Common Stock they receive in the Merger than they would have received on the AM Common Units or AMGP Common Shares, as applicable, that they currently own, through the same period. Additionally, New AM intends to target an average DCF coverage ratio of 1.2-1.3x through 2022, which is higher than the targeted DCF coverage ratio projected at Antero Midstream.

New AM will not be required to pay dividends on the New AM Common Stock under the New AM certificate of incorporation or the DGCL. Subject to preferences that may be applicable to any outstanding shares or series of preferred stock, New AM Stockholders will only be entitled to receive ratably such dividends (payable in cash, stock or otherwise), if any, as may be declared from time to time by the New AM Board out of funds legally available for dividend payments. The New AM Board will make a determination each quarter as to the actual amount, if any, of dividends to pay on the New AM Common Stock, based on various factors, some of which are beyond its control, including New AM's operating cash flows, New AM's working capital needs, New AM's ability to access capital markets for debt and equity financing on reasonable terms, the restrictions contained in New AM's debt instruments, if any, New AM's debt service requirements, credit metrics and the cost of acquisitions, if any. New AM may not have sufficient cash each quarter to pay dividends or maintain current or expected levels of dividends. Accordingly, we cannot guarantee that any dividends will be declared or paid in the future.

Q:    Are there risks associated with the Transactions that I should consider in deciding how to vote?

A:

Yes. You should carefully read the detailed description of the risks associated with the Transactions, as described under the heading "Risk Factors" beginning on page 168 and

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"Comparison of the Rights of New AM Stockholders, AMGP Shareholders and AM Unitholders" beginning on page 217 of this joint proxy statement/prospectus.

Q:    When and where will the special meetings be held?

A:

AMGP Shareholders:    The AMGP Special Meeting will be held at 1615 Wynkoop Street, Denver, Colorado 80202, on                        ,                         , at                        , local time.

AM Unitholders:    The AM Special Meeting will be held at 1615 Wynkoop Street, Denver, Colorado 80202, on                        ,                         , at                         , local time.

Q:    Who is entitled to vote at the special meetings?

A:

AMGP Shareholders:    The record date for the AMGP Special Meeting is                        ,                         . Only AMGP Shareholders of record as of the close of business on the record date are entitled to notice of, and to vote at, the AMGP Special Meeting.

AM Unitholders:    The record date for the AM Special Meeting is                        ,                         . Only AM Unitholders of record as of the close of business on the record date are entitled to notice of, and to vote at, the AM Special Meeting.

Q:    What constitutes a quorum at the special meetings?

A:

AMGP Shareholders:    The holders of a majority of the outstanding AMGP Common Shares, represented in person or by proxy (by submitting a properly executed proxy card or properly submitting your proxy by telephone or Internet), as of the record date will constitute a quorum and will permit AMGP to conduct the proposed business at the AMGP Special Meeting. Proxies received but marked as abstentions will be counted as AMGP Common Shares that are present and entitled to vote for purposes of determining the presence of a quorum. Broker non-votes will be counted as AMGP Common Shares that are present and entitled to vote for purposes of determining the presence of a quorum.

AM Unitholders:    The holders of a majority of the outstanding AM Common Units represented in person or by proxy (by submitting a properly executed proxy card or properly submitting a proxy by telephone or Internet) will constitute a quorum and will permit Antero Midstream to conduct the proposed business at the AM Special Meeting. Proxies received but marked as abstentions will be counted as AM Common Units that are present and entitled to vote for purposes of determining the presence of a quorum. Broker non-votes will not be considered present at the AM Special Meeting for purposes of determining the presence of a quorum and will not be included in the vote.

Q:    What is the vote required to approve each proposal?

A:

AMGP Shareholders:    Approval of the Conversion Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares. Approval of the AMGP Transaction Proposal requires the affirmative vote of holders of a majority of the outstanding AMGP Common Shares held by the Disinterested AMGP Shareholders. Approval of both the LTIP Proposal and the Issuance Proposal requires the affirmative vote of holders of a majority of the AMGP Common Shares voted on such proposals at the AMGP Special Meeting. Completion of the Transactions is not conditioned upon approval of the LTIP Proposal. Even if the AMGP Shareholders approve the LTIP Proposal, AMGP will not adopt a New AM LTIP unless the Transactions are completed.

As of                        ,                         , all of the directors, executive officers and affiliates of AMGP GP beneficially owned, in the aggregate, approximately        % of the outstanding AMGP

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Common Shares. Pursuant to the AMGP Voting Agreement, the AMGP Voting Agreement Shareholders have agreed to vote in favor of each of the AMGP Proposals. AMGP believes that all of the remaining directors and executive officers of AMGP GP will also vote in favor of each of the AMGP Proposals.

AM Unitholders:    Approval of the AM Merger Proposal requires the affirmative vote of both the holders of a majority of the outstanding AM Common Units and a majority of the outstanding AM Common Units held by the Disinterested AM Unitholders.

As of                        ,                         , all of the directors and executive officers of AMP GP beneficially owned, in the aggregate, approximately        % of the outstanding AM Common Units. Pursuant to the AR Voting Agreement, Antero Resources and certain of AMP GP's directors and executive officers beneficially owning, in the aggregate, approximately        % of the outstanding AM Common Units have agreed to vote or cause to be voted all AM Common Units beneficially owned by such persons in favor of the AM Merger Proposal. Antero Midstream believes that all of the remaining directors and executive officers of AMP GP will vote in favor of the AM Merger Proposal.

Q:    What happens if I sell my AM Common Units after the record date but before the AM Special Meeting?

A:

If you transfer your AM Common Units after the record date but before the date of the AM Special Meeting, you will retain your right to vote at the AM Special Meeting, but you will not have the right to receive the Merger Consideration. In order to receive the Merger Consideration, you must hold your AM Common Units through the completion of the Merger.

Q:    What happens if I sell my AMGP Common Shares after the record date but before the AMGP Special Meeting?

A:

If you transfer your AMGP Common Shares after the record date but before the date of the AMGP Special Meeting, you will still retain your right to vote at the AMGP Special Meeting, but you will not receive any shares of New AM Common Stock with respect to such AMGP Common Shares in connection with the Transactions.

Q:    How do I vote my AMGP Common Shares or AM Common Units if I hold them in my own name?

A:

AMGP Shareholders:    After you have read this joint proxy statement/prospectus carefully, please respond by completing, signing and dating your proxy card and returning it in the enclosed postage-paid envelope, or by submitting your proxy by telephone or the Internet as soon as possible in accordance with the instructions provided under "The AMGP Special Meeting—Proxy Submission Procedures—Proxy Submission by AMGP Shareholders of Record."

AM Unitholders:    After you have read this joint proxy statement/prospectus carefully, please respond by completing, signing and dating your proxy card and returning it in the enclosed postage-paid envelope, or by submitting your proxy by telephone or the Internet as soon as possible in accordance with the instructions provided under "The AM Special Meeting—Proxy Submission Procedures—Proxy Submission by AM Unitholders of Record."

Q:    If my AMGP Common Shares or AM Common Units are held in "street name" by my bank, broker or other nominee, will my bank, broker or other nominee vote them for me?

A:

AMGP Shareholders:    If your AMGP Common Shares are held in "street name" in a brokerage account or by a broker, bank or other nominee, you must provide the record holder of your AMGP Common Shares with instructions on how to vote your shares. Please follow the voting

29

instructions provided by your broker, bank or other nominee. Please note that you may not vote AMGP Common Shares held in street name by returning a proxy card directly to AMGP or by voting in person at the AMGP Special Meeting unless you provide a "legal proxy," which you must obtain from your broker, bank or other nominee. Your broker, bank or other nominee is obligated to provide you with a voting instruction card for you to use.

Under the rules of the NYSE, brokers who hold shares in street name for a beneficial owner of those shares typically have the authority to vote in their discretion on "routine" proposals when they have not received instructions from beneficial owners. However, brokers are not allowed to exercise their voting discretion with respect to the approval of matters that the NYSE determines to be "non-routine" without specific instructions from the beneficial owner. It is expected that each of the AMGP Proposals is a "non-routine" matter. Broker non-votes occur when a broker or nominee is not instructed by the beneficial owner of shares to vote on a particular proposal for which the broker does not have discretionary voting power.

If you are an AMGP Shareholder and you do not instruct your broker, bank or other nominee on how to vote your shares, your broker, bank or other nominee may not vote your shares on the AMGP Proposals, which broker non-votes, if any, will have the same effect as a vote cast "AGAINST" both the Conversion Proposal and the AMGP Transaction Proposal. A broker non-vote will have no effect on the vote count for the Issuance Proposal or the LTIP Proposal.

AM Unitholders:    If your AM Common Units are held in "street name" in a brokerage account or by a broker, bank or other nominee, you must provide the record holder of your AM Common Units with instructions on how to vote your AM Common Units. Please follow the voting instructions provided by your broker, bank or other nominee. Please note that you may not vote AM Common Units held in street name by returning a proxy card directly to Antero Midstream or by voting in person at the AM Special Meeting unless you provide a "legal proxy," which you must obtain from your broker, bank or other nominee. Your broker, bank or other nominee is obligated to provide you with a voting instruction card for you to use.

Under the rules of the NYSE, brokers who hold units in street name for a beneficial owner of those units typically have the authority to vote in their discretion on "routine" proposals when they have not received instructions from beneficial owners. However, brokers are not allowed to exercise their voting discretion with respect to the approval of matters that the NYSE determines to be "non-routine" without specific instructions from the beneficial owner. It is expected that all proposals to be voted on at the AM Special Meeting are such "non-routine" matters. Broker non-votes occur when a broker or nominee is not instructed by the beneficial owner of units to vote on a particular proposal for which the broker does not have discretionary voting power.

If you are an AM Unitholder and you do not instruct your broker, bank or other nominee on how to vote your units, your broker, bank or other nominee may not vote your units on the AM Merger Proposal, which broker non-votes, if any, will have the same effect as a vote "AGAINST" this proposal.

Q:    When do you expect the Transactions to be completed?

A:

We currently expect the Transactions to close in the first quarter of 2019. A number of conditions must be satisfied before AMGP and Antero Midstream can complete the Transactions, including the approval of the Conversion Proposal, the AMGP Transaction Proposal and the Issuance Proposal by the AMGP Shareholders and the approval of the AM Merger Proposal by the AM Unitholders. Although AMGP and Antero Midstream cannot be sure when all of the conditions to the Transactions will be satisfied, AMGP and Antero Midstream expect to complete the Transactions as soon as practicable following the AMGP Special Meeting and AM Special Meeting (assuming the AMGP Proposals and the AM Merger Proposal are approved by the AMGP

30

Shareholders and AM Unitholders, respectively), subject to, among other things, the registration statement of which this joint proxy statement/prospectus forms a part having been declared effective under the Securities Act. See "The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions—Conditions to the Merger" and "Risk Factors—Risks Related to the Transactions." Failure to complete the Transactions, or significant delays in completing the Transactions, could negatively affect each party's future business and financial results and the trading prices of the AMGP Common Shares and AM Common Units.

Q:    How do the AMGP Conflicts Committee and the AMGP Board recommend that the AMGP Shareholders vote?

A:

The AMGP Conflicts Committee and the AMGP Board each recommends that the AMGP Shareholders vote FOR each of the AMGP Proposals.

On October 8, 2018, the AMGP Conflicts Committee unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, (iii) recommended to the AMGP Board that the AMGP Board approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, and submit the AMGP Proposals to a vote of the AMGP Shareholders and (iv) recommended to the Disinterested AMGP Shareholders that the Disinterested AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents. For more information regarding the recommendation of the AMGP Conflicts Committee, see "Special Factors—Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions."

AMGP Shareholders should be aware that some of AMGP GP's directors and executive officers may have interests in the Transactions that are different from, or in addition to, the interests they may have as AMGP Shareholders. See "Special Factors—Interests of Certain Persons in the Transactions"

Q:    How do the AM Conflicts Committee and the AM Board recommend that the AM Unitholders vote?

A:

The AM Conflicts Committee and the AM Board each recommends that the AM Unitholders vote FOR the AM Merger Proposal.

On October 8, 2018, the AM Conflicts Committee unanimously (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AM and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, (iii) recommended to the AM Board that the AM Board approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, and submit the AM Merger Proposal to a vote of the AM Unitholders and (iv) recommended to the Disinterested AM Unitholders that the Disinterested AM Unitholders approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents. For more information regarding the recommendation of the AM Conflicts Committee

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in making such determination under the Antero Midstream Partnership Agreement, see "Special Factors—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions"

AM Unitholders should be aware that some of AMP GP's directors and executive officers may have interests in the Simplification that are different from, or in addition to, the interests they may have as AM Unitholders. See "Special Factors—Interests of Certain Persons in the Transactions."

Q:    What will happen to Antero Midstream as a result of the Merger?

A:

At the closing of the Merger, an indirect, wholly owned subsidiary of New AM will be merged with and into Antero Midstream, with Antero Midstream surviving as an indirect, wholly owned subsidiary of New AM. Upon completion of the Merger, AM Common Units currently listed on the NYSE will cease to be listed on the NYSE and will be subsequently deregistered under the Exchange Act.

Q.    What are the expected U.S. federal income tax consequences for an AM Public Unitholder that is a U.S. holder (as defined in the section titled "Material U.S. Federal Income Tax Consequences") of the ownership of shares of New AM Common Stock after the Merger is completed?

A.

New AM will be classified as a corporation for U.S. federal income tax purposes, and thus New AM (and not its stockholders) will be subject to U.S. federal income tax on its taxable income. Distributions with respect to New AM Common Stock will constitute dividends for U.S. federal income tax purposes to the extent paid from New AM's current or accumulated earnings and profits (as determined under U.S. federal income tax principles). To the extent that the amount of a distribution exceeds New AM's current and accumulated earnings and profits, such distribution will first be treated as a non-taxable return of capital to the extent of (and reducing, but not below zero) the U.S. holder's adjusted tax basis in its New AM Common Stock and thereafter be treated as capital gain from the sale or exchange of such New AM Common Stock.

See the section titled "Material U.S. Federal Income Tax Consequences" for a more complete discussion of certain U.S. federal income tax consequences of owning and disposing of shares of New AM Common Stock.

Q:    Are AM Unitholders entitled to appraisal rights?

A:

No. AM Unitholders are not entitled to appraisal rights in connection with the Merger under applicable law or contractual appraisal rights under the Antero Midstream Partnership Agreement or the Simplification Agreement.

Q:    What if I do not vote?

A:

If you sign and return your proxy card without indicating how to vote on any particular proposal, the AMGP Common Shares represented by your proxy will be voted as recommended by the AMGP Board with respect to that proposal or the AM Common Units represented by your proxy will be voted as recommended by the AM Board with respect to that proposal. Unless an AMGP Shareholder or AM Unitholder, as applicable, checks the box on its proxy card to withhold discretionary authority, the applicable proxy holders may use their discretion to vote on other matters relating to the AMGP Special Meeting or AM Special Meeting, as applicable.

For purposes of each of the AMGP Special Meeting and the AM Special Meeting, an abstention occurs when a shareholder or unitholder, as applicable, attends the applicable special meeting in person and does not vote or returns a proxy with an "abstain" instruction.

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AMGP

Conversion Proposal:    An abstention or failure to vote will have the same effect as a vote cast "AGAINST" the Conversion Proposal.

AMGP Transaction Proposal:    An abstention or failure to vote will have the same effect as a vote cast "AGAINST" the AMGP Transaction Proposal.

LTIP Proposal:    An abstention will be deemed to not have been cast on such matter. If an AMGP Shareholder is not present in person at the AMGP Special Meeting and does not respond by proxy, it will have no effect on the vote count for the LTIP Proposal (assuming a quorum is present).

Issuance Proposal:    An abstention will be deemed to not have been cast on such matter. If an AMGP Shareholder is not present in person at the AMGP Special Meeting and does not respond by proxy, it will have no effect on the vote count for the Issuance Proposal (assuming a quorum is present).

Antero Midstream

AM Merger Proposal:    An abstention or failure to vote will have the same effect as a vote cast "AGAINST" the AM Merger Proposal.

Q:    If I am planning to attend a special meeting in person, should I still vote by proxy?

A:

Yes. Regardless of whether you plan to attend the AMGP Special Meeting or the AM Special Meeting, as applicable, you should vote by proxy. Your AMGP Common Shares or AM Common Units will not be voted if you do not vote by proxy or do not vote in person at the AMGP Special Meeting or the AM Special Meeting, as applicable.

Q:    Who may attend the AMGP Special Meeting and the AM Partners Special Meeting?

A:

AMGP Shareholders (or their authorized representatives) and AMGP's invited guests may attend the AMGP Special Meeting. AM Unitholders (or their authorized representatives) and Antero Midstream's invited guests may attend the AM Special Meeting. All attendees should be prepared to present government-issued photo identification (such as a driver's license or passport) for admittance.

Q:    Can I change my instructions after I have submitted my proxy?

A:

Yes. If you own your AMGP Common Shares or AM Common Units in your own name, you may revoke your proxy at any time prior to its exercise by:

•

giving written notice of revocation to the Secretary of AMGP GP or the Secretary of AMP GP, as applicable, at or before the AMGP Special Meeting or the AM Special Meeting, as applicable;

•

appearing and voting in person at the AMGP Special Meeting or the AM Special Meeting, as applicable; or

•

properly completing and executing a later dated proxy and delivering it to the Secretary of AMGP GP or the Secretary of AMP GP, as applicable, at or before the AMGP Special Meeting or the AM Special Meeting, as applicable.

Your presence without voting at the AMGP Special Meeting or the AM Special Meeting, as applicable, will not automatically revoke your proxy, and any revocation during the meeting will not affect votes previously taken.

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Q:    What will happen to Antero Midstream if the Merger does not occur?

A:

If the AMGP Proposals are not approved by the requisite AMGP Shareholders or the AM Merger Proposal is not approved by the requisite AM Unitholders, or if the Merger is not completed for any other reason, AM Unitholders will not receive any form of consideration for their AM Common Units in connection with the Merger. Instead, Antero Midstream will remain a public limited partnership and the AM Common Units will continue to be listed and traded on the NYSE.

Q:    How and when do I make my election with respect to the Merger Consideration?

A:

You will receive a form of election in a separate mailing. You should carefully review and follow the instructions accompanying that form of election. You will make your consideration election by properly completing, signing and returning the form of election along with your evidence of units in book-entry form representing AM Common Units to American Stock Transfer & Trust Company, LLC, the exchange agent in connection with the Merger. The Election Deadline will be 5:00 p.m., New York City time, on the later of the twentieth day following the mailing of the form of election and ten days prior to the anticipated closing date of the Transactions, or such other time as mutually agreed by AMGP and Antero Midstream. AMGP and Antero Midstream will publicly announce the anticipated Election Deadline at least five business days prior to the Election Deadline in a press release, on AMGP's and Antero Midstream's websites and in filings with the SEC. If you receive New AM Common Stock as part of the Merger Consideration, the market price of the Merger Consideration you ultimately receive will depend on the closing price of New AM Common Stock on the date the Transactions are consummated. As such, you will not know the exact market value of the Merger Consideration you will receive at the time you make your election.

Q:    Can I change my election after the form of election has been submitted?

A:

Yes, as long as you do so before the Election Deadline. You may revoke your election prior to the Election Deadline by submitting a written notice of revocation to the exchange agent or by submitting new later-dated election materials. Revocations must specify the name in which your AM Common Units are registered on the unit transfer books of Antero Midstream and such other information as the exchange agent may request. If you wish to submit a new election, you must do so in accordance with the election procedures described in this joint proxy statement/prospectus and in the form of election that you will receive in a separate mailing. If you instructed a bank, broker, nominee, trust company or other fiduciary to submit an election for your AM Common Units, you must follow the directions of your bank, broker, nominee, trust company or other fiduciary for changing those instructions. Whether you revoke your election by submitting a written notice of revocation or by submitting new election materials, the notice of materials must be received by the exchange agent by the Election Deadline in order for the revocation or new election to be valid.

Q:    May I transfer my AM Common Units after I make my election?

A:

Yes, however, any transfer prior to the Election Deadline of AM Common Units made by an AM Public Unitholder who has made an election will automatically revoke such election. AM Public Unitholders who have made elections will be unable to sell or otherwise transfer their AM Common Units after the Election Deadline, unless the election is properly revoked before the Election Deadline or unless the Simplification Agreement is terminated.

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Q:    What if I do not send a form of election or it is not received?

A:

If the exchange agent does not receive a properly completed form of election from you before the Election Deadline, together with any unit certificates (or evidence of units in book-entry form) representing the units you wish to exchange for the Merger Consideration, properly endorsed for transfer, book-entry transfer shares or a guarantee of delivery and any additional documents required by the procedures set forth in the form of election, then you will be deemed to have made a Public Mixed Consideration election with respect to your AM Common Units. You bear the risk of delivery and should send any form of election by courier or by hand delivery to the appropriate address shown in the form of election.

If you do not make a valid election with respect to any AM Common Units you own of record, you will receive written instructions from the exchange agent after completion of the proposed Transactions on how to exchange your AM Common Units for the Merger Consideration.

Q:    May I submit a form of election even if I do not vote for the approval of the Transactions?

A:

Yes. You may submit a form of election even if you vote against the approval of the Transactions or if you abstain from voting.

Q:    What should I do if I receive more than one set of voting materials for the AMGP Special Meeting or the AM Special Meeting?

A:

You may receive more than one set of voting materials for the AMGP Special Meeting or the AM Special Meeting and the materials may include multiple proxy cards. For example, you will receive a separate voting instruction card for each brokerage account in which you hold AMGP Common Shares or AM Common Units. Additionally, if you are a holder of record registered in more than one name, you will receive more than one proxy card. Finally, if you hold both AMGP Common Shares and AM Common Units, you will receive two separate packages of proxy materials. Please complete, sign, date and return each proxy card and voting instruction card that you receive according to the instructions on it.

Q:    Whom do I call if I have further questions about voting, the special meetings or the Transactions?

A:

AMGP Shareholders and AM Unitholders who have questions about the Transactions, including the procedures for voting their common shares or units, or who desire additional copies of this joint proxy statement/prospectus or additional proxy cards should contact:

AMGP Shareholders	AM Unitholders
MacKenzie Partners, Inc.	MacKenzie Partners, Inc.
1407 Broadway—27th Floor	1407 Broadway—27th Floor
New York, New York 10018	New York, New York 10018
Toll free: (800) 322-2885	Toll free: (800) 322-2885
Collect: (212) 929-5500	Collect: (212) 929-5500
proxy@mackenziepartners.com	proxy@mackenziepartners.com
or	or
Antero Midstream GP LP	Antero Midstream Partners LP
1615 Wynkoop Street	1615 Wynkoop Street
Attention: Investor Relations	Attention: Investor Relations
Denver, Colorado 80202	Denver, Colorado 80202
Telephone: (303) 357-7310	Telephone: (303) 357-7310

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SPECIAL NOTE REGARDING FORWARD-LOOKING STATEMENTS

        This joint proxy statement/prospectus and the documents incorporated herein by reference contain various forward-looking statements and information that reflect AMGP's and/or Antero Midstream's current beliefs, expectations or intentions regarding future events. These forward-looking statements may be identified by the use of words such as "may," "will," "could," "should," "would," "expect," "plan," "project," "intend," "anticipate," "believe," "estimate," "forecast," "predict," "potential," "pursue," "target," "continue," "contemplate" and similar expressions that contemplate future events. These statements appear in a number of places in this joint proxy statement/prospectus and in the documents incorporated by reference.

        All statements other than statements of historical fact included or incorporated by reference in this joint proxy statement/prospectus, including statements regarding AMGP and/or Antero Midstream's financial position, business strategy and other plans and objectives for future operations (including management of New AM) or transactions, and statements regarding the approval of the Simplification Agreement and the Transactions, the satisfaction of the closing conditions to the Transactions, the timing of the completion of the Merger, expected U.S. federal income tax consequences, expectations and intentions regarding outstanding litigation, expectations with respect to costs and other anticipated effects of the Merger and expectations regarding future dividends paid to New AM Stockholders, are forward-looking statements.

        Although AMGP and Antero Midstream believe that such forward-looking statements are based on reasonable assumptions, neither AMGP nor Antero Midstream gives any assurance that such expectations will in fact occur. Certain factors could cause actual results to differ materially from those in the forward-looking statements. Such factors include, but are not limited to:

•

the possibility that the Transactions are not consummated in a timely manner or at all;

•

the diversion of management in connection with the Transactions and New AM's ability to realize the anticipated benefits of the Transactions;

•

the impact on New AM of increased levels and costs of indebtedness used to fund the Transactions including the cash portion of the Merger Consideration and increased cost of existing indebtedness due to the actions taken to consummate the Transactions;

•

Antero Midstream's ability to obtain debt or equity financing on satisfactory terms to fund additional acquisitions, expansion projects, working capital requirements and the repayment or refinancing of indebtedness;

•

Antero Resources' expected production and ability to execute its drilling and development plan;

•

Antero Midstream's business strategies;

•

Antero Midstream's ability to realize the anticipated benefits of investing in unconsolidated affiliates;

•

natural gas, NGLs, and oil prices;

•

competition and government regulations;

•

actions taken by third party producers, operators, processors and transporters;

•

legal or environmental matters;

•

costs of conducting gathering and compression operations;

•

general economic conditions;

•

credit markets;

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•

operating hazards, natural disasters, weather related delays, casualty losses and other matters beyond our control; and

•

uncertainty regarding Antero Midstream's future operating results.

        Antero Midstream and AMGP caution you that these forward-looking statements are subject to all of the risks and uncertainties, most of which are difficult to predict and many of which are beyond Antero Midstream's and AMGP's control, incident to the gathering and processing and fresh water and wastewater treatment businesses. These risks include, but are not limited to, the expected timing and likelihood of completion of the Transactions, including the ability to obtain requisite regulatory, lender, unitholder and shareholder approval and the satisfaction of the other conditions to the consummation of the proposed Transactions, risks that the proposed Transactions may not be consummated or the benefits contemplated therefrom may not be realized, the cost savings, tax benefits and any other synergies from the Transactions may not be fully realized or may take longer to realize than expected, Antero Resources' expected future growth, Antero Resources' ability to meet its drilling and development plan, commodity price volatility, ability to execute Antero Midstream's business strategy, competition and government regulations, actions taken by third-party producers, operators, processors and transporters, inflation, environmental risks, drilling and completion and other operating risks, regulatory changes, the uncertainty inherent in projecting future rates of production, cash flow and access to capital, the timing of development expenditures, and the other risks described under "Risk Factors" in Antero Midstream's and AMGP's most recently filed Quarterly Reports on Form 10-Q, Annual Reports on Form 10-K, subsequent Current Reports on Form 8-K and other SEC filings. All subsequent written and oral forward-looking statements concerning AMGP, Antero Midstream, the proposed Merger and other Transactions, or other matters attributable to AMGP or Antero Midstream or any person acting on their behalf are expressly qualified in their entirety by the cautionary statements above. The forward-looking statements speak only as of the date made and, other than as required by law, neither AMGP nor Antero Midstream undertakes any obligation to update publicly or revise any of these forward-looking statements, whether as a result of new information, future events or otherwise.

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SPECIAL FACTORS

Effects of the Transactions

        The below sections describe the Transactions contemplated by the Simplification Agreement. On the closing date of the Transactions, the primary transactions will be completed in order as follows:

        GP Merger.    First, at AMP GP's option, prior to the Conversion, AMP GP will merge with and into AMGP, with AMGP continuing as the surviving entity and the separate existence of AMP GP ceasing.

        The Conversion.    Second, following the GP Merger (if any), AMGP will convert from a Delaware limited partnership to a Delaware corporation under the laws of the State of Delaware named "Antero Midstream Corporation." In the Conversion, each AMGP Shareholder will receive an equivalent number of shares of New AM Common Stock, a certificate of incorporation of New AM will be filed with the Delaware Secretary of State and the bylaws of New AM will become effective.

        The Merger.    Third, following the Conversion, Merger Sub will merge with and into Antero Midstream, with Antero Midstream surviving the Merger as a wholly owned subsidiary of NewCo. In exchange for each AM Common Unit held, each AM Public Unitholder will be entitled to receive, at its election and subject to proration, one of: (i) the Public Mixed Consideration, (ii) the Public Stock Consideration, or (iii) the Public Cash Consideration. In exchange for each AM Common Unit held, Antero Resources will be entitled to receive, subject to certain adjustments (as described below), the AR Mixed Consideration.

        The aggregate cash consideration to be paid to Antero Resources and the AM Public Unitholders will be fixed at an amount equal to the Available Cash Consideration, which is approximately $598 million in the aggregate. If the Public Available Cash exceeds the cash consideration elected to be received by the AM Public Unitholders, Antero Resources may elect to increase the total amount of cash it receives as a part of the AR Mixed Consideration up to an amount equal to the Excess Available Cash and the amount of shares it will receive will be reduced accordingly based on the AMGP VWAP. In addition, the consideration each AM Public Unitholder will receive may be prorated in the event that more cash or equity is elected to be received than what would otherwise have been paid if all AM Public Unitholders elected to receive the Public Mixed Consideration, and Antero Resources had received the AR Mixed Consideration.

        AMGP owns all of the limited liability company interests in AMP GP. Immediately after the completion of the Merger, New AM will indirectly own 100% of Antero Midstream's outstanding limited partner interests through its ownership of NewCo and IDR Holdings.

        The Simplification Agreement provides, at AMP GP's option, for the merger of AMP GP with and into AMGP, with AMGP continuing as the surviving entity and the separate existence of AMP GP ceasing. If AMP GP elects to consummate the GP Merger, at the effective time of the Merger, AMGP will become the holder of the general partner interest in Antero Midstream and will be the sole general partner of the surviving entity as set forth in the Antero Midstream Partnership Agreement, as amended (which will be the agreement of limited partnership of the surviving entity as of the effective time of the Merger if the GP Merger is consummated).

        Based on the volume weighted average price of an AMGP Common Share for the 20 consecutive NYSE full trading days ending at the close of regular trading hours on the NYSE on October 8, 2018 (the last trading day before the announcement of the entry into the Simplification Agreement), the Merger Consideration represents a premium of approximately 6% above the volume weighted average price of the AM Common Units for the same period.

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        AM Common Units are currently registered under the Exchange Act and are quoted on NYSE under the symbol "AM." As a result of the Transactions, AM will be a privately held limited partnership and there will be no public market for the AM Common Units. After the Transactions, AM Common Units will cease to be quoted on the NYSE and price quotations with respect to sales of AM Common Units in the public market will no longer be available. In addition, the registration of the AM Common Units under the Exchange Act will be terminated. Antero Midstream will continue to have public debt outstanding that will require separate public reporting by Antero Midstream, unless the holders of such debt consent to allowing Antero Midstream to satisfy this reporting obligation through New AM's public reports.

        The Series B Exchange.    Concurrently with the Merger, all of the issued and outstanding Series B Units will be exchanged for an aggregate of approximately 17.35 million shares of New AM Common Stock. A total of 98,600 Series B Units are currently outstanding. The Series B Exchange Shares will remain subject to the same vesting requirements as the Series B Units for which they are exchanged. For more information, please see "The AMGP Proposals and the AM Merger Proposal: The Simplification Agreement and the Transactions—Structure of the Merger—The Series B Exchange" beginning on page 193 of this joint proxy statement/prospectus.

        The discussion in this joint proxy statement/prospectus of the Transactions and the material terms of the Simplification Agreement is subject to, and is qualified in its entirety by reference to, the Simplification Agreement, a copy of which is attached as Annex A to this joint proxy statement/prospectus and incorporated by reference herein.

Background of the Transactions

        In connection with its initial public offering in 2013, Antero Resources and its sponsors, including certain funds affiliated with Warburg Pincus LLC, certain funds affiliated with Yorktown Partners LLC, Paul M. Rady and Glen C. Warren, Jr., formed Antero Midstream as a separate company to own, operate and develop midstream energy assets to service Antero Resources' growing production, primarily under long-term, fixed-fee and cost-plus contracts. While Antero Resources retained a 100% economic interest in Antero Midstream, Antero Resources Investment LLC, an entity controlled by the Sponsor Holders and Messrs. Rady and Warren ("Antero Investment"), held a special membership interest in Antero Midstream, the terms of which provided that, following the initial public offering of Antero Midstream, the special membership interest would automatically convert into a general partner interest and incentive distribution rights in Antero Midstream. In November 2014, Antero Midstream completed its initial public offering and Antero Investment retained a non-economic general partner interest and all of the incentive distribution rights in Antero Midstream. As a result, Antero Resources does not have an economic interest in Antero Midstream's incentive distribution rights.

        In December 2016, Antero Investment formed IDR Holdings to hold 100% of Antero Midstream's incentive distribution rights. IDR Holdings was formed with two classes of membership interests: (i) capital interests referred to as Series A Units, all of which were granted to AMGP in its capacity as managing member of IDR Holdings, and (ii) profits interests referred to as Series B Units, certain of which were granted to Messrs. Rady and Warren in December 2016, and the remainder of which were granted to certain other members of Antero Management in January 2017. Prior to entering into the IDR Holdings LLCA Amendment, the Series B Holders were entitled to receive in the aggregate up to 6% of all quarterly cash distributions in excess of $7.5 million distributed by Antero Midstream on its incentive distribution rights. The Series B Holders also had the ability to cause the exchange of vested Series B Units for AMGP Common Shares with a value equal to such holder's pro rata share of up to 6% of AMGP's market capitalization at the time of exchange (calculated by reference to the 20-day volume weighted average price of the AMGP Common Shares preceding the date of exchange request) in excess of $2.0 billion, at any time up until December 31, 2026. The Series B Units were subject to

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restrictions on transfer and vested over three years in one-third increments upon each anniversary of the vesting commencement date, subject to continued employment.

        In May 2017, Antero Investment determined to monetize a portion of its interest in the incentive distribution rights and general partner interest in Antero Midstream, and caused AMGP, which owned AMP GP and the rights to receive the substantial majority of the distributions on the incentive distribution rights in Antero Midstream, to conduct an initial public offering of the AMGP Common Shares. As Antero Midstream's cash distributions grow, the percentage of those distributions payable to the holders of the incentive distribution rights, and indirectly AMGP, increase.

        Following the initial public offering of AMGP, a number of external factors contributed to Antero Resources, AMGP and Antero Midstream evaluating potential transactions that would further their respective strategic objectives.

        First, since May 2017, the landscape for master limited partnerships ("MLPs") has changed considerably. The Tax Cuts and Jobs Act lowered the U.S. federal corporate income tax rate from 35% to 21%, reducing the benefit of an MLP pass-through structure. In addition, the U.S. Federal Energy Regulatory Commission disallowed MLPs from receiving an income tax allowance on pipelines with tolling fees set under the "cost of service" framework. Although Antero Midstream was not directly impacted by the disallowance, many MLPs were, and the ruling either had or coincided with a negative impact on investments in MLPs in general. Between the completion of AMGP's initial public offering on May 9, 2017 and October 8, 2018 (the last trading day before the Simplification Agreement was announced), the Alerian MLP Index, a leading gauge of energy MLPs whose constituents represent approximately 75% of total energy MLP market capitalization, declined by approximately 9%, and between the completion of Antero Midstream's initial public offering on November 10, 2014 and October 8, 2018, the Alerian MLP Index declined by over 44%. These negative market trends have contributed to a significant number of MLPs eliminating their incentive distribution rights, directly or through mergers with the entities holding their incentive distribution rights, converting to corporations (for income tax and state law purposes) or both.

        On January 26, 2018, Antero Resources contacted a representative of Vinson & Elkins LLP ("V&E") to discuss recent stockholder feedback encouraging Antero Resources to both return capital to stockholders and simplify its current organizational structure into a two-entity (upstream and midstream) structure and eliminate Antero Midstream's incentive distribution rights.

        On January 29, 2018, SailingStone Capital Partners filed a Schedule 13D with respect to its ownership interests in Antero Resources, indicating its intention to engage in discussions with the AR Board regarding, among other things, strategic alternatives that would eliminate perceived potential conflicts of interest resulting from the current corporate structure.

        Also on January 29, 2018, members of Antero Management contacted each of J.P. Morgan and Morgan Stanley, as well as a number of other qualified investment banks, to discuss the potential engagement of those firms as financial advisors to Antero Resources in connection with potential measures to address the stockholder concerns described above regarding Antero Resources' discounted trading value relative to its peers in the Appalachian Basin and the perceived stockholder misalignment resulting from Antero Resources not having an economic interest in Antero Midstream's incentive distribution rights. The return of capital to Antero Resources' stockholders was also discussed as an objective. Each of J.P. Morgan and Morgan Stanley discussed their respective experience and qualifications, including with respect to activist defense assignments, MLPs, the energy industry generally, as well as its substantial experience advising MLPs and other companies with respect to transactions similar to the Transactions. The representatives of Morgan Stanley also noted that they had previously been engaged by Antero Resources, AMGP and their respective affiliates, and disclosed the nature of those engagements, as well as the related fees, to Antero Management.

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        Later on January 29, 2018, Antero Resources issued a press release announcing that it was working with financial and legal advisors to evaluate potential measures to address the perceived valuation discount of Antero Resources' common stock relative to some of the premier U.S. large cap upstream independents that have a similar profile in terms of leverage, capital efficiency, production growth and free cash flow generation.

        Antero Resources entered into a definitive engagement letter with J.P. Morgan, effective February 2, 2018, for J.P. Morgan to serve as financial advisor to Antero Resources in connection with a potential simplification involving Antero Resources, AMGP and/or Antero Midstream and certain related transactions (the "Potential Simplification"). On February 21, 2018, the AR Board convened a meeting with members of Antero Management to discuss requests from Antero Resources stockholders to consider and evaluate potential measures to (i) remedy the perceived valuation discount and relative underperformance of Antero Resources compared to its peers in the Appalachian Basin, (ii) remedy the perceived stockholder misalignment resulting from Antero Resources not having an economic interest in Antero Midstream's incentive distribution rights and (iii) return capital to Antero Resources' stockholders. Representatives of J.P. Morgan and Morgan Stanley participated in this meeting and led a discussion of upstream and midstream sector trends, an overview of Antero Resources benchmarked against its peers and a preliminary review of potential alternative transactions that could be considered by AMGP, Antero Midstream and Antero Resources and a preliminary analysis of a merger involving AMGP and Antero Midstream. At this meeting, the AR Board decided to establish the AR Special Committee for the purpose of engaging in a strategic process to explore, review and evaluate a range of strategies and transactions to address a perceived discount in the trading value of Antero Resources' common stock. Robert J. Clark, Benjamin A. Hardesty and Joyce E. McConnell were appointed as the three members of the AR Special Committee. Mr. Clark was appointed Chairman of the AR Special Committee.

        On February 28, 2018, Antero Management discussed with representatives of Morgan Stanley whether Morgan Stanley would be willing to advise Antero Midstream instead of Antero Resources in connection with a Potential Simplification. While Morgan Stanley had provided preliminary analysis of strategic alternatives to the AR Board, given that Antero Resources had determined to engage J.P. Morgan as its financial advisor, and given that the transaction structure of the Potential Simplification had not yet been determined, Antero Management believed it would be more appropriate and valuable to have Morgan Stanley available to advise Antero Midstream. On March 19, 2018, Morgan Stanley was formally engaged by Antero Midstream.

        On February 23, 2018, the AM Board and AMGP Board convened separate meetings with Antero Management, at which time Antero Management advised each of those two boards of the AR Board's decision to undertake an evaluation of strategic alternatives and informed them of the possibility that Antero Resources may determine to support or encourage a potential transaction involving one or more of Antero Midstream or AMGP, and that, due to the relationships described under "Special Factors—Relationship of the Parties to the Transactions," the consideration of any such transaction by the AM Board or AMGP Board could result in actual or perceived conflicts of interest. At these meetings, as a result of the potential conflicts of interest, the AM Board and AMGP Board, respectively, formed and authorized the AM Conflicts Committee and the AMGP Conflicts Committee to, among other things: (i) consider, explore, review, analyze, and evaluate one or more Potential Simplification transactions, (ii) make such investigation of potential alternatives to the Potential Simplification, including maintaining the status quo, as those committees deemed necessary or appropriate, (iii) authorize, empower or direct the officers and employees of AMGP GP and AMP GP, as applicable, to provide those committees with such information and assistance as may be requested by those committees, (iv) review, evaluate, solicit, structure, and, if deemed sufficiently favorable to the interests of AMGP and Antero Midstream, as applicable, negotiate, or delegate the ability to negotiate to any persons, the terms and provisions, and determine the advisability, of one or more Potential

41

Simplifications, (v) determine whether or not to approve one or more Potential Simplification transactions by Special Approval (as defined in each of the AMGP Partnership Agreement and Antero Midstream Partnership Agreement), (vi) make a recommendation to the full AMGP Board and AM Board, as applicable, to approve or disapprove a Potential Simplification and (vii) if so approved by the committees, together with the approval by the full AMGP Board and AM Board, as applicable, to take such other actions as are necessary or advisable to consummate a Potential Simplification.

        At the meeting of the AM Board, the AM Board appointed David A. Peters and John C. Mollenkopf as the two members of the AM Conflicts Committee. Mr. Peters was appointed Chairman of the AM Conflicts Committee. At the meeting of the AMGP Board, the AMGP Board appointed Brooks J. Klimley and Rose M. Robeson as the two members of the AMGP Conflicts Committee. Mr. Klimley was appointed Chairman of the AMGP Conflicts Committee. In each case, those appointments followed determinations by the AM Board and AMGP Board, as applicable, in their business judgment, that each such director is "independent" within the NYSE's definition of that term and that those individuals satisfy the independence requirements for service on an audit committee under Rule 10A-3 of the Exchange Act and for service on a conflicts committee under the Antero Midstream Partnership Agreement and AMGP Partnership Agreement, as applicable. In making those determinations, each of the AM Board and AMGP Board considered, among other things (i) the qualifications, background, experience and independence of each such director, as set forth on the director and officer questionnaires most recently completed by those individuals, (ii) the holdings by each such director of equity securities of each of Antero Resources, AMGP and Antero Midstream, (iii) the AM Board's and AMGP Board's prior affirmative determination of the independence of each such director and (iv) such other information as the AM Board and AMGP Board deemed appropriate regarding the qualifications, background and experience of each such director.

        Following that delegation, Mr. Peters, on behalf of the AM Conflicts Committee, contacted representatives of Gibson, Dunn & Crutcher, LLP ("Gibson Dunn") to discuss engaging Gibson Dunn as legal counsel to represent the AM Conflicts Committee in connection with considering various alternatives, including a potential transaction involving Antero Resources and/or AMGP. The AM Conflicts Committee engaged Gibson Dunn because of Gibson Dunn's knowledge, expertise and experience with respect to public merger and acquisition transactions, MLP transactions and conflicts committee engagements and its prior experience with a representative of Gibson Dunn. An engagement letter detailing the terms of Gibson Dunn's engagement was executed on March 7, 2018.

        On February 25, 2018, Mr. Clark contacted representatives of Sidley Austin LLP ("Sidley") to ask that firm to check conflicts regarding potentially representing the AR Special Committee in connection with the Potential Simplification. On February 26, 2018, a representative of Sidley confirmed that it was clear to represent the AR Special Committee if the committee chose to retain Sidley.

        Also on February 26, 2018, Antero Resources, Antero Midstream and AMGP issued press releases announcing the formation of the AR Special Committee, the AM Conflicts Committee and the AMGP Conflicts Committee, respectively.

        On February 26, 2018, Ms. Robeson, on behalf of the AMGP Conflicts Committee, contacted a representative of Hunton Andrews Kurth LLP ("Hunton Andrews Kurth") to discuss engaging Hunton Andrews Kurth to represent the AMGP Conflicts Committee in connection with the Potential Simplification. On February 27, 2018, a representative of Hunton Andrews Kurth confirmed that it was able to represent the AMGP Conflicts Committee if the AMGP Conflicts Committee chose to engage Hunton Andrews Kurth.

        On February 28, 2018, the AMGP Conflicts Committee held a telephonic meeting with a representative of Hunton Andrews Kurth in attendance. The AMGP Conflicts Committee made the determination to engage Hunton Andrews Kurth as legal advisor following consideration of information regarding Hunton Andrews Kurth's independence and qualifications, including their experience with

42

public mergers and acquisitions, complex transactions involving publicly traded partnerships and representation of conflicts committees. There was preliminary discussion of structural alternatives for a Potential Simplification.

        Also on February 28, 2018, the AR Special Committee held its first meeting, with representatives of Sidley participating. The AR Special Committee retained Sidley as its legal counsel because of Sidley's extensive experience in M&A transactions for exploration and production companies and midstream companies, including representing special committees in those types of transactions. At the meeting, Sidley discussed with the AR Special Committee, among other items, confidentiality, fiduciary duties, member independence, the Antero Resources director indemnification agreements and the delegated authority of the AR Special Committee from the AR Board. Additionally, the AR Special Committee discussed candidates to serve as its financial advisor. Mr. Clark and Mr. Hardesty pointed to Baird's experience in M&A transactions for exploration and production companies and midstream companies. They also noted that Baird had served as financial advisor for a special committee of the AR Board that had been appointed in 2015 in connection with negotiating a contribution of Antero Resources' water assets to Antero Midstream. That previously-appointed special committee had consisted of Mr. Clark and Mr. Hardesty. Following the discussion, the AR Special Committee determined to retain Baird as its financial advisor, subject to confirmation of their independence and the negotiation of a mutually acceptable engagement letter.

        On March 1, 2018, the AMGP Conflicts Committee held a telephonic meeting with representatives of Hunton Andrews Kurth in attendance. During the meeting, the AMGP Conflicts Committee interviewed three financial advisory firms with experience in advising special committees and conflicts committees and analyzing transactions involving publicly traded partnerships and related parties. Following each respective firm's presentation, discussion ensued regarding the information presented, the qualifications and experience of the firms, discussion of factors bearing on the independence of the firms, questions related to the Potential Simplification, benefits of receiving financial advice from the firms, the relationships of the firms with AMGP and its affiliates and the fees requested by the firms. Further, the AMGP Conflicts Committee discussed engaging Delaware counsel. After further discussion and consideration of its qualifications and experience, the AMGP Conflicts Committee made the determination to engage Richards, Layton & Finger, P.A. ("Richards Layton") as Delaware counsel based on their experience with complex transactions involving publicly traded partnerships and representation of conflicts committees.

        On March 2, 2018, the AMGP Conflicts Committee held a telephonic meeting with a representative of Hunton Andrews Kurth in attendance. There was additional discussion of the competence, expertise and other qualifications of each of the financial advisory firms interviewed, including experience with financial analysis, negotiations, complex transaction structures, the energy industry, and capital markets. Hunton Andrews Kurth advised the AMGP Conflicts Committee of legal considerations regarding the selection of financial advisors. After further discussion, the AMGP Conflicts Committee determined it would seek to engage Goldman Sachs as its financial advisor, subject to negotiation of a mutually acceptable engagement letter. The AMGP Conflicts Committee and Goldman Sachs subsequently entered into an engagement letter.

        On March 4, 2018, the AMGP Conflicts Committee held a telephonic meeting with representatives of Hunton Andrews Kurth and Richards Layton in attendance. The AMGP Conflicts Committee and its advisors discussed the background of the Potential Simplification and began to evaluate the Potential Simplification, including discussion regarding the process for potentially making an initial proposal to the AM Conflicts Committee regarding the Potential Simplification. There was discussion with counsel of the process to be followed in considering the Potential Simplification and the role of the AMGP Conflicts Committee.

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        On March 6, 2018, the AM Conflicts Committee held a telephonic meeting during which representatives of Gibson Dunn explained the AM Conflicts Committee's roles and duties in, and best practices for, carrying out its exploration, review and evaluation of one or more Potential Simplification transactions. Mr. Peters, on behalf of the AM Conflicts Committee, expressed a desire to engage a financial advisor to assist the AM Conflicts Committee with its review of those transactions and discussed the process for evaluating potential financial advisors with Gibson Dunn.

        On March 8, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. The AMGP Conflicts Committee and its advisors engaged in a discussion regarding an upcoming presentation from Antero Management regarding the Potential Simplification. One of the AMGP Conflicts Committee's goals for the presentation included gaining a better understanding of the work previously done by Antero Management regarding a Potential Simplification and alternative transaction structures.

        On the afternoon of March 8, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn to further discuss the potential engagement of a financial advisor. The AM Conflicts Committee had previously met with and received presentations from three potential financial advisors regarding their experience and qualifications. The presentation from Tudor Pickering detailed Tudor Pickering's experience and qualifications, including with respect to public merger and acquisition transactions, MLPs, the energy industry generally, as well as its substantial experience advising MLPs and other companies with respect to transactions similar to the Transactions. The representatives of Tudor Pickering also noted that Tudor Pickering had previously been engaged by Antero Resources, AMGP and their respective affiliates and disclosed the nature of those engagements to the AM Conflicts Committee. Following the presentation, representatives of Gibson Dunn sought and received detailed information from Tudor Pickering regarding prior and potential future engagements of Tudor Pickering by Antero Midstream or its affiliates, as well as regarding potential relationships between relevant individuals at Tudor Pickering and individuals at Antero Midstream or its affiliates. During the course of discussing Tudor Pickering's engagement, representatives of Gibson Dunn sought and received further additional detailed information regarding these matters. Both in advance of the AM Conflicts Committee's engagement of Tudor Pickering and thereafter, those relationships and fees were discussed by the AM Conflicts Committee with representatives of Gibson Dunn. Following those discussions, the AM Conflicts Committee determined that those relationships and fees would not inhibit Tudor Pickering's ability to serve as financial advisor to the AM Conflicts Committee.

        On March 9, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance by invitation of the AMGP Conflicts Committee were members of Antero Management, members of the AMGP Board and V&E, outside corporate counsel for each of Antero Resources, Antero Midstream and AMGP, who was continuing to advise each entity in connection with the strategic review and any Potential Simplification. Antero Management discussed with the AMGP Conflicts Committee its analysis of the Potential Simplification, including the current outlook for the midstream market and potential simplification structures analyzed by Antero Management. Among other things, Antero Management's initial presentation reflected that, pursuant to the terms of the IDR Holdings LLC Agreement, the value of the Series B Units following the Potential Simplification would be equivalent to up to 6% of AMGP's post-transaction market capitalization in excess of $2 billion. Antero Management also discussed the potential option value inherent in the Series B Units due to the ability of the Series B Holders to exchange into AMGP Common Shares at any time up until December 31, 2026. Following the presentation, the AMGP Conflicts Committee and its advisors met to discuss the information presented. There was discussion of forecasts and financial information prepared by Antero Management for use by the AMGP Conflicts Committee and Goldman Sachs.

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        On March 12, 2018, the AM Conflicts Committee decided to engage Tudor Pickering as its financial advisor because of Tudor Pickering's knowledge and experience with respect to public merger and acquisition transactions, particularly transactions involving MLPs. An engagement letter detailing the terms of Tudor Pickering's engagement was executed on March 19, 2018, after the AM Conflicts Committee, with Gibson Dunn's assistance, had reviewed and negotiated acceptable terms thereof.

        Also on March 12, 2018, the AR Special Committee met, with representatives of Sidley participating, to discuss the AR Special Committee's engagement letter with Baird. At this meeting, the AR Special Committee also discussed correspondence with, and a questionnaire provided to, Baird regarding potential conflicts of interest in Baird's representation of the AR Special Committee. The AR Special Committee agreed that Baird could represent it fairly and without conflict, and approved the form of engagement letter. The Baird engagement letter was executed on March 15, 2018.

        On March 14, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss the mandate given by the AR Board with respect to the AR Special Committee and potential actions for the AR Special Committee to consider, including several different transaction alternatives. The AR Special Committee sought advice from Sidley with respect to how to approach the AR Special Committee's mandate, including discussions about which of the three committees (i.e., the AR Special Committee, the AM Conflicts Committee or the AMGP Conflicts Committee) should be the committee to make an initial proposal to one or more of the other committees.

        On March 14, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors and certain members of Antero Management to conduct due diligence. Antero Management presented and discussed with the AMGP Conflicts Committee its outlook for growth of Antero Midstream and AMGP, a detailed business overview and a five-year financial plan for Antero Midstream.

        On March 16, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the presentation of Antero Management's business outlook for AMGP and Antero Midstream. Later on March 16, 2018, Goldman Sachs delivered an executed disclosure letter regarding certain of its relationships with AMGP, Antero Midstream, Antero Resources and Warburg Pincus LLC to the AMGP Conflicts Committee. After considering the information presented in the letter with its legal counsel, the AMGP Conflicts Committee re-confirmed the firm's engagement as its financial advisor.

        On March 20, 2018, the AM Board held a meeting, with representatives of V&E, Tudor Pickering and Gibson Dunn participating, as well as Antero Management and representatives of Morgan Stanley, the financial advisor to Antero Midstream. During the meeting, members of Antero Management provided to the AM Board, including the members of the AM Conflicts Committee and its advisors, certain due diligence information with respect to Antero Resources, Antero Midstream and AMGP, including financial projections and information with respect to the assets, business plan, growth projects and outlook. Morgan Stanley provided an evaluation of selected simplification strategies which would combine Antero Midstream and AMGP and/or eliminate the incentive distribution rights and the potential benefits with respect thereto. Morgan Stanley noted its conclusion that a transaction structure in which AMGP acquired the AM Common Units would be the optimal mechanism for Antero Midstream and the AM Unitholders among those being considered. Following Morgan Stanley's presentation, representatives of Gibson Dunn highlighted for the AM Board certain results of their due diligence review with respect to the independence of the members of the AM Conflicts Committee. Gibson Dunn noted that Mr. Peters' son is employed by Antero Resources. The AM Board determined that this relationship was not material because the employment relationship is maintained on an arm's length basis, Mr. Peters' son is not an executive officer of Antero Resources or a member of Mr. Peters' household, and Mr. Peters does not have any material interest in the employment

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relationship. The AM Board meeting concluded with Antero Management's presentation to the AM Board of an overview of potential financing alternatives for Antero Midstream.

        Later on March 20, 2018, following the meeting of the AM Board, the AM Conflicts Committee held a separate meeting with representatives of Gibson Dunn and Tudor Pickering to discuss the presentation provided by Antero Management and Morgan Stanley and to outline the process of the AM Conflicts Committee's consideration of a proposal with respect to a transaction between AMGP and Antero Midstream to the extent such a transaction was presented.

        On March 22, 2018, the AR Special Committee held a meeting, with representatives of Baird, Sidley, J.P. Morgan and V&E participating, as well as members of Antero Management, to discuss the analysis performed to date by Antero Management and J.P. Morgan with regard to a range of potential transactions. This meeting was intended to permit the AR Special Committee and its financial and legal advisors to better understand the work already performed by Antero Management, V&E and J.P. Morgan with respect to potential structural and financing transactions, including consolidation of the midstream business, commencement by Antero Resources of a share repurchase program and the acceleration of certain earn-out payments (the "Water Earn-Out") provided for under the Contribution, Conveyance and Assumption Agreement, dated September 17, 2015, between Antero Resources and Antero Midstream (the "Water Contribution Agreement").

        From March 22, 2018 to April 19, 2018, the AR Special Committee met five times to discuss Baird's observations relating to structural issues in the Antero family of companies (including Antero Resources, Antero Midstream and AMGP), the performance of Antero Resources' stock price and various potential strategies to increase performance at Antero Resources. From March 22, 2018 to March 30, 2018, Antero Management provided to Baird stand-alone forecasts of Antero Resources, stand-alone forecasts of Antero Midstream and AMGP, a summary of an AMGP-Antero Midstream merger model, certain intercompany agreements of the Antero parties, as well as a structural steps memorandum for an AMGP acquisition of Antero Midstream. The AR Special Committee set as a priority in any potential transaction that Antero Resources receive cash as consideration for its unit ownership in Antero Midstream in order to permit Antero Resources to implement strategic initiatives that the AR Board had previously considered, including potential repurchases of Antero Resources common stock.

        On March 23, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Representatives of Goldman Sachs discussed preliminary financial analyses regarding a Potential Simplification with the AMGP Conflicts Committee. The AMGP Conflicts Committee and its advisors discussed possible alternative structures for a Potential Simplification. There was also discussion of potential settlement of the Series B Units and possible governance structures following a Potential Simplification. Legal advisors to the AMGP Conflicts Committee made a presentation regarding certain legal matters, including duties and responsibilities of the AMGP Conflicts Committee.

        On March 30, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss updates on a Potential Simplification, as well as a preliminary evaluation of a potential transaction that Antero Resources would propose to Antero Midstream regarding the Water Earn-Out. The AR Special Committee determined that one of the benefits of accelerating the Water Earn-Out would be the acceleration of the cash payments to Antero Resources, in exchange for giving Antero Midstream a discount on the total amount it would be required to pay under the Water Contribution Agreement. In the meantime, the AR Special Committee continued to discuss the potential of a larger transaction that focused on a simplification of the corporate structure of the midstream business, including the various alternatives that had been presented by J.P. Morgan during the March 22, 2018 presentation.

        On April 3, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss financial due diligence and the preliminary financial analyses prepared by

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representatives of Goldman Sachs for a Potential Simplification, including potential settlement of the Series B Units. The AMGP Conflicts Committee and its advisors also discussed possible alternative structures for a Potential Simplification, including (1) an acquisition of Antero Midstream by AMGP in a 100% stock transaction, and (2) a recapitalization involving elimination of IDRs in exchange for AM Common Units. Additionally, there was a discussion of the differences in a typical investor base in a Delaware corporation and a typical investor base in a Delaware limited partnership. The AMGP Conflicts Committee determined that resolving the settlement of the Series B Units would be a gating item to making a proposal to the AM Conflicts Committee with respect to the Potential Simplification.

        Later on April 3, 2018, Mr. Klimley had a discussion with Mr. Warren regarding a Potential Simplification, the settlement of the Series B Units in a Potential Simplification and the AMGP Conflicts Committee's view that the renegotiation of the IDR Holdings LLC Agreement and settlement of the Series B Units were gating items to the transaction. Unless otherwise indicated, in negotiations relating to the settlement of the Series B Units described in "—Background of the Transactions," Mr. Rady and Mr. Warren were acting in their capacity as holders of a majority of the outstanding Series B Units. Mr. Warren stated that the Series B Units represented equity owned by the Series B Holders that is not subject to any limitations or conditions other than continued employment and time vesting restrictions and that the full stated value of the Series B Units is up to 6% of the post-transaction market capitalization of AMGP in excess of $2 billion. Mr. Warren noted that the contractual exchange right of the Series B Holders was currently exercisable at any time up until December 31, 2026, allowing the Series B Holders to participate in AMGP's potential growth over that time period.

        On April 4, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to report on discussions held between Mr. Klimley and Mr. Warren regarding the settlement of the Series B Units.

        On April 5, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the settlement of the Series B Units, structural alternatives and negotiation of terms of a Potential Simplification. The AMGP Conflicts Committee discussed the view of Mr. Warren regarding the position of the Series B Holders regarding the settlement of the Series B Units in a Potential Simplification.

        On April 8, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Representatives of Goldman Sachs discussed with the AMGP Conflicts Committee preliminary financial analyses of a Potential Simplification, including the potential settlement of the Series B Units. There was also discussion of potentially soliciting the views of the other non-management members of the AMGP Board affiliated with the Sponsor Holders (the "AMGP Sponsor Directors") in connection with the AMGP Conflicts Committee's analysis of the Series B Units.

        On April 10, 2018, the AR Special Committee met again, with representatives of Baird and Sidley participating, to discuss the potential acceleration of the Water Earn-Out, as well as a preliminary discussion regarding the settlement of the Series B Units in a Potential Simplification. In the event of a combination of Antero Midstream and AMGP, the AR Special Committee believed that the Series B Units could potentially dilute Antero Resources' ownership in a pro forma combined entity, and the AR Special Committee focused on understanding the potential impact of an exchange of the Series B Units on a potential transaction.

        Also on April 10, 2018, the AMGP Conflicts Committee held an in-person meeting in Denver, Colorado with representatives of all of its advisors. Representatives of Goldman Sachs discussed with the AMGP Conflicts Committee preliminary financial analyses from Goldman Sachs regarding the Potential Simplification, including the potential settlement of the Series B Units in the transaction.

        Later on April 10, 2018, following the earlier meeting of the AMGP Conflicts Committee, the AMGP Board held a meeting, with representatives of V&E, Goldman Sachs, Hunton Andrews Kurth

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and Richards Layton participating, as well as Antero Management. The AMGP Conflicts Committee and representatives of Goldman Sachs updated the AMGP Board regarding their ongoing work to evaluate the Potential Simplification. Mr. Klimley discussed the work that the AMGP Conflicts Committee had performed so far in evaluating alternative transaction structures, as well as its views on the market conditions for MLPs and recent trends in simplifications and related transactions in the midstream industry to enhance distribution stability. At the request of the AMGP Conflicts Committee, representatives of Goldman Sachs discussed observations of the AMGP Conflicts Committee as to potential market reactions to alternative transaction structures, noting that various factors suggested the acquisition of Antero Midstream by AMGP was likely to be viewed more favorably by the market than the alternative transaction structures discussed at the meeting on April 3, 2018. There was also a discussion of the advisability of determining the expected settlement of the Series B Units prior to the AMGP Conflicts Committee being able to make a proposal for any Potential Simplification.

        Following the meeting of the AMGP Board on April 10, 2018, the AMGP Conflicts Committee and all of its advisors met with the AMGP Sponsor Directors. At the request of the AMGP Conflicts Committee, representatives of Goldman Sachs discussed preliminary financial analyses of the Potential Simplification, including the potential settlement of the Series B Units in the transaction. Following discussion, it was agreed that Mr. Kagan, an AMGP Sponsor Director, and Mr. Klimley would have further discussions with Messrs. Rady and Warren regarding the settlement of the Series B Units.

        Later on April 10, 2018, Mr. Klimley, Mr. Kagan and Mr. Warren discussed the Series B Units. Mr. Warren stated that the Series B Holders understood the desire of the various committees to eliminate the incentive distribution rights and Series B Units as part of a Potential Simplification, and Mr. Warren continued to emphasize his belief that, taking into account the Management Holders' calculated value of the Series B Units, a Potential Simplification would continue to be financially attractive to AMGP Shareholders if the Series B Units were settled on their existing terms.

        On April 11, 2018, the AMGP Conflicts Committee held a telephonic meeting with representatives of Hunton Andrews Kurth and Richards Layton to discuss certain terms of the Series B Units. There was discussion of the obligations of the AMGP Conflicts Committee in considering a Potential Simplification. Mr. Klimley also reported on the discussion with Mr. Warren regarding the Series B Units. Further discussion ensued about the contractual terms of the Series B Units and potential alternative transaction structures.

        On April 11, 2018, after discussions with the AMGP Conflicts Committee and the AMGP Sponsor Directors, Messrs. Rady and Warren proposed that, in order to facilitate a Potential Simplification, instead of the formula provided in the IDR Holdings LLC Agreement, which generally would allow holders of vested Series B Units a right to exchange a Series B Unit for a per unit equivalent of up to 6% of the then pro forma market capitalization of AMGP less $2 billion, the same formula would be applied to the exchange of the Series B Units except that all vested and unvested Series B Units would be eliminated and 6% would be reduced to 4.5% in the formula. In addition, Messrs. Rady and Warren offered to settle the Series B Units in connection with the closing of the Potential Simplification, well in advance of December 31, 2026.

        On April 12, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss its next steps with respect to a Potential Simplification and the potential elimination of the Series B Units as part of the transaction. The AMGP Conflicts Committee discussed the proposal made by Messrs. Rady and Warren with respect to the settlement of the Series B Units.

        On April 18, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Representatives of Goldman Sachs discussed preliminary financial analyses of the Potential Simplification, including the potential settlement of the Series B Units. The AMGP Conflicts Committee discussed possible terms for making a proposal to the Series B Holders with respect to the settlement of the Series B Units in the transaction.

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        On April 19, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to review Baird's presentation concerning market and valuation perspectives for each of Antero Resources, Antero Midstream and AMGP, as well as a discussion of return of capital alternatives. Additionally, the AR Special Committee and representatives of Baird and Sidley discussed a potential proposal to Antero Midstream to accelerate the Water Earn-Out. The AR Special Committee unanimously decided to send a proposal to the AM Conflicts Committee relating to the Water Earn-Out (the "Water Earn-Out Proposal"). The Water Earn-Out Proposal contemplated that Antero Midstream's obligations under the Water Earn-Out would be cancelled for a total cash payment to Antero Resources equal to $220 million, representing a $30 million discount to the total maximum amount of the Water Earn-Out payments that Antero Midstream would be required to make if the applicable thresholds were achieved. The Water Earn-Out Proposal was sent to the AM Conflicts Committee on April 19, 2018.

        On April 19, 2018, the AM Conflicts Committee received a letter from Mr. Clark, on behalf of the AR Special Committee, outlining the Water Earn-Out Proposal. On April 20, 2018 and April 25, 2018, the AM Conflicts Committee held telephonic meetings with representatives of Gibson Dunn and Tudor Pickering, respectively, to review and consider the terms of the Water Earn-Out Proposal. Following those discussions, the AM Conflicts Committee determined that negotiations with respect to the Water Earn-Out Proposal were premature, and that any such negotiations should take place as part of negotiations with respect to a broader transaction between Antero Midstream, on the one hand, and AMGP and/or Antero Resources, on the other hand. The AM Conflicts Committee then requested that Gibson Dunn prepare a response to the AR Special Committee for their consideration. On April 26, 2018, Mr. Peters communicated the AM Conflicts Committee's position with respect to the Water Earn-Out Proposal to Mr. Clark by email. In light of Mr. Peters' response, the AR Special Committee determined not to pursue the acceleration of the Water Earn-Out at that time, but instead would consider whether to revive the Water Earn-Out Proposal if a broader transaction were to be proposed by one of the other committees.

        On April 20, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Following discussion, the AMGP Conflicts Committee agreed to propose to the Series B Holders that the Series B Units be exchanged for shares of New AM Common Stock in connection with a Potential Simplification. There was discussion of a draft term sheet to be used by the AMGP Conflicts Committee to make a proposal that the Series B Units be exchanged for a fixed nine million shares of New AM Common Stock.

        After the meeting of the AMGP Conflicts Committee on April 20, 2018, Mr. Klimley delivered the proposal to Messrs. Warren and Rady as majority holders of the Series B Units. Messrs. Rady and Warren responded that they did not want to exchange the Series B Units for a fixed number of shares of New AM Common Stock because they believed the Series B Units should benefit from AMGP Share price appreciation that may occur in connection with a Potential Simplification up until closing of the Potential Simplification. Messrs. Warren and Rady also explained the potential value of the Series B Units as a result of the potential for future issuances of shares of New AM Common Stock and the effect that future share issuances may have on the economics associated with the Series B Units over the long term.

        On April 23, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the response from Messrs. Rady and Warren to the AMGP Conflicts Committee's proposal regarding the settlement of the Series B Units. Mr. Klimley reported on the discussions he held with Messrs. Rady and Warren. It was agreed that Mr. Klimley would contact Messrs. Rady and Warren and request that they provide a written counteroffer to the AMGP Conflicts Committee.

        On April 26, 2018, the AMGP Conflicts Committee had a conversation with the Management Holders regarding the AMGP Conflicts Committee's proposal for the Series B Units. Following the discussion, Messrs. Rady and Warren provided the AMGP Conflicts Committee with a written term

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sheet proposing the mechanics for settling the Series B Units. The term sheet was accompanied by the Management Holders' financial analysis of the Series B Units.

        On April 27, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. The AMGP Conflicts Committee discussed the term sheet relating to the Series B Units and authorized Goldman Sachs to contact the Management Holders with due diligence questions regarding their financial analysis of the Series B Units.

        On April 30, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. At the request of the AMGP Conflicts Committee, representatives of Goldman Sachs discussed preliminary financial analyses regarding a Potential Simplification, including the potential settlement with respect to the Series B Units in the transaction. The AMGP Conflicts Committee and all of its advisors discussed, among other things, the economics associated with the Series B Units and next steps with respect to negotiation of the settlement of the Series B Units.

        On May 3, 2018, Mr. Klimley had a discussion with Mr. Warren regarding Mr. Warren's preliminary agreement on certain aspects of the value of the Series B Units. There was discussion of the need to agree on other financial assumptions before proceeding with further negotiations.

        Later on May 3, 2018, the AMGP Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Hunton Andrews Kurth. The AMGP Conflicts Committee discussed the potential for a portion of the exchange of the Series B Units to be settled in cash and whether a cash settlement might reduce dilution and offer certain benefits to the Disinterested AMGP Shareholders.

        On May 8, 2018, Mr. Klimley had a discussion with Mr. Kagan regarding the potential consideration being evaluated for payment to the Series B Holders in connection with the settlement of the Series B Units.

        Later on May 8, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Representatives of Goldman Sachs discussed updated preliminary financial analyses with regard to a Potential Simplification, including the potential settlement with respect to the Series B Units in the transaction and preliminary financial analyses regarding Antero Midstream and AMGP.

        Later on May 8, 2018, the AMGP Conflicts Committee held a telephonic meeting with representatives of Goldman Sachs and Hunton Andrews Kurth in attendance. Representatives of Goldman Sachs discussed preliminary financial analyses regarding the Series B Units. The AMGP Conflicts Committee determined to seek further information from other non-management members of the AMGP Board regarding the settlement of the Series B Units.

        On May 9, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were certain of the AMGP Sponsor Directors. The AMGP Conflicts Committee and the AMGP Sponsor Directors discussed alternative structures for a Potential Simplification and the potential exchange of the Series B Units for a fixed number of shares of New AM Common Stock.

        On May 18, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were the AMGP Sponsor Directors. At the request of the AMGP Conflicts Committee, representatives of Goldman Sachs discussed preliminary financial analyses regarding a Potential Simplification. The potential structures for the transaction discussed at the meeting included the post-transaction company being a Delaware C-corporation with a corporate-style governance structure and a majority of the board of directors being independent.

        On May 21, 2018, the AMGP Conflicts Committee held a telephonic meeting with representatives of Hunton Andrews Kurth and Richards Layton in attendance. The AMGP Conflicts Committee and its legal counsel discussed the benefits of conditioning a Potential Simplification on approval by a

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majority of the Disinterested AMGP Shareholders. Following discussion with its legal counsel, the AMGP Conflicts Committee determined that it would seek to negotiate for a Potential Simplification to be conditioned on approval by a majority of the Disinterested AMGP Shareholders.

        On May 22, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, upon invitation by the AMGP Conflicts Committee, were certain of the AMGP Sponsor Directors. There was discussion regarding certain perceived investor preferences for corporate-style board governance, a majority of independent board members, and the potential for inclusion in stock market indices, if certain financial and trading metrics were met. After further discussion, the AMGP Conflicts Committee believed it would be desirable to propose to the Series B Holders that the Series B Units be exchanged for a fixed number of shares of New AM Common Stock in the range of 17 to 18 million shares. The willingness of the AMGP Conflicts Committee to support the proposed exchange of the Series B Units on those terms was conditioned upon agreement on an acceptable exchange ratio for the Merger, the Potential Simplification resulting in a NYSE-listed Delaware C-corporation with a corporate-style governance structure and a board of directors consisting of a majority of independent directors and upon the Transactions being conditioned on the approval of a majority of the Disinterested AMGP Shareholders.

        From May 22, 2018 to May 29, 2018, Mr. Klimley had discussions with Messrs. Rady and Warren about the Potential Simplification. Messrs. Rady and Warren expressed their opposition to AMGP's conversion to a C-corporation instead of remaining a limited partnership. Messrs. Rady and Warren also renewed their proposal that the Series B Units be exchanged for 4.5% of AMGP's post-transaction market capitalization in excess of $2 billion which would allow holders of Series B Units to benefit from AMGP Share price appreciation that may occur in connection with a Potential Simplification. Alternatively, if the AMGP Conflicts Committee proposed to exchange the Series B Units for a fixed number of shares of New AM Common Stock or shares of New AM Common Stock, Messrs. Rady and Warren proposed to exchange the Series B Units for 19.5 million shares, which Messrs. Rady and Warren believed allowed the holders of Series B Units to capture a sufficient amount of the anticipated upside in AMGP's market capitalization that they would be giving up by agreeing to exchange the Series B Units for a fixed number of shares of New AM Common Stock. Messrs. Rady and Warren agreed that a Potential Simplification would be conditioned upon approval of a majority of the Disinterested AMGP Shareholders.

        On May 29, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were certain of the AMGP Sponsor Directors. Mr. Klimley reported on recent discussions he had with Messrs. Rady and Warren. After discussion with all of its advisors, the AMGP Conflicts Committee, after considering the views of the AMGP Sponsor Directors, believed it would be desirable to propose to Messrs. Rady and Warren that the Series B Units be exchanged for a fixed number of shares of New AM Common Stock in the amount of 18 million shares, that AMGP be converted to a Delaware C-corporation with a corporate-style governance structure with a majority of independent directors and that the Potential Simplification be conditioned on receiving the approval of a majority of the Disinterested AMGP Shareholders. Later, on May 29, 2018, Mr. Klimley delivered the AMGP Conflicts Committee's proposal to Messrs. Rady and Warren.

        On May 30, 2018, Mr. Klimley had a discussion with Messrs. Rady and Warren. Messrs. Rady and Warren declined the AMGP Conflicts Committee's proposal as it related to the conversion of AMGP to a C-corporation, but indicated that they would be amenable to exchanging the Series B Units for a fixed number of shares of New AM Common Stock.

        On May 31, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were the AMGP Sponsor Directors. Mr. Klimley reported on discussions he had with Messrs. Rady and Warren.

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Following discussion, the AMGP Conflicts Committee directed Hunton Andrews Kurth to conduct further due diligence regarding C-corporation structure and tax matters.

        Later on May 31, 2018, Mr. Klimley had discussions with Messrs. Rady and Warren about a Potential Simplification. Messrs. Rady and Warren indicated their agreement to the conversion of AMGP to a Delaware C-corporation with a corporate-style governance structure and, along with the Sponsor Holders, to forgo the significant governance rights they would have retained had New AM remained a limited partnership and had the Management Holders and Sponsor Holders continued to own its general partner, subject to the completion of further due diligence on tax matters. Messrs. Rady and Warren also proposed exchanging the Series B Units for 19 million shares of New AM Common Stock.

        Later on May 31, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, was one of the AMGP Sponsor Directors. Mr. Klimley reported on the discussions he had earlier in the day with Messrs. Rady and Warren. The AMGP Conflicts Committee determined that Mr. Klimley would discuss with Messrs. Rady and Warren whether they would be willing to accept a proposal that the Series B Units would be exchanged for 18.5 million shares of New AM Common Stock.

        On June 1, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were the AMGP Sponsor Directors. Representatives of Goldman Sachs discussed preliminary financial analyses regarding the potential settlement of the Series B Units in a Potential Simplification. After discussion with all of its advisors, the AMGP Conflicts Committee and the non-management members of the AMGP Board agreed to propose to Messrs. Rady and Warren that the Series B Units be exchanged for 18.5 million shares of New AM Common Stock.

        Later on June 1, 2018, Mr. Klimley delivered the AMGP Conflicts Committee's proposal to Messrs. Rady and Warren. Messrs. Rady and Warren indicated they were prepared to accept the proposal that the Series B Units be exchanged for a fixed number of shares of New AM Common Stock equal to 18.5 million shares and that the post-transaction company would be structured as a C-corporation.

        Later on June 1, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were the AMGP Sponsor Directors. Mr. Klimley reported on the discussion he had earlier in the day with Messrs. Rady and Warren. The AMGP Conflicts Committee authorized Hunton Andrews Kurth to conduct further tax due diligence in discussions with V&E regarding the anticipated transaction structure and the anticipated tax impacts.

        On June 6, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Representatives of Goldman Sachs discussed preliminary financial analyses of a Potential Simplification, including the potential settlement of the Series B Units in the transaction. After further discussion, the AMGP Conflicts Committee agreed that it would make a proposal to Antero Midstream that provides for each outstanding AM Common Unit to be exchanged for 1.6 shares of the post-transaction company. The AMGP Conflicts Committee and its advisors discussed a form of proposal letter to be used in connection with making a proposal to Antero Midstream for the Potential Simplification.

        Later on June 6, 2018, the AMGP Board held a meeting, with representatives from V&E and Hunton Andrews Kurth participating, as well as members of Antero Management. At the meeting, V&E discussed with members of the AMGP Board potential transaction structures and the anticipated tax impacts of those structures, including that the transaction structure the AMGP Conflicts Committee was considering proposing to Antero Midstream and Antero Resources would be taxable to AM Unitholders, including Antero Resources.

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        Following the AMGP Board meeting, on June 6, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss a revised draft proposal letter to be used in connection with making a proposal to Antero Midstream for a Potential Simplification. There was discussion of the tax analysis and due diligence conducted earlier in the day regarding the anticipated tax treatment of the transaction. Representatives of Goldman Sachs also discussed preliminary financial analyses regarding the Potential Simplification that, at the request of the AMGP Conflicts Committee, it would also discuss at an upcoming AMGP Board meeting.

        On June 7, 2018, the AMGP Board held a meeting, with representatives from V&E, Goldman Sachs, Hunton Andrews Kurth and Richards Layton participating, as well as members of Antero Management. At the meeting, the members of the AMGP Conflicts Committee and representatives of Goldman Sachs updated the AMGP Board regarding their ongoing evaluations of the Potential Simplification, as well as an overview of the initial proposal that the AMGP Conflicts Committee had prepared and planned to present to the AM Board. At the request of the AMGP Conflicts Committee, representatives of Goldman Sachs provided an overview of the illustrative terms of the proposal under consideration by the AMGP Conflicts Committee, with a particular focus on the relative historical trading prices of the shares of New AM Common Stock and the AM Common Units and the implied ratios at which the AM Common Units would be exchanged for shares of New AM Common Stock. The AMGP Conflicts Committee determined to revise its proposal to reflect the discussion that had taken place at the meeting before submitting the proposal to the AM Board. Following this discussion, representatives of V&E led a discussion on the anticipated tax treatment of the Potential Simplification.

        The following day, on June 8, 2018, the AMGP Conflicts Committee submitted its proposal to Antero Midstream that provided, among other things, for each outstanding AM Common Unit to be exchanged for shares of the post-transaction company at an exchange ratio of 1.6x, without any cash component (the "AMGP June 8 Proposal"). The AMGP June 8 Proposal also provided that AMGP would be reorganized into a C-corporation with corporate style governance and that all of the Series B Units would be exchanged for an aggregate of 18.5 million shares of fully vested New AM Common Stock without being subject to any further conditions or transfer restrictions, as well as an immediate cash payment of any accrued but unpaid distributions with respect to unvested Series B Units.

        Between June 8, 2018 and June 28, 2018, the AM Conflicts Committee held several telephonic meetings with representatives of Gibson Dunn and Tudor Pickering to discuss the terms of the AMGP June 8 Proposal. Over the course of those meetings, representatives of Tudor Pickering presented Tudor Pickering's preliminary analysis of the financial terms of the AMGP June 8 Proposal, including the proposed merger consideration and the expected impact on the AM Public Unitholders after giving effect to the exchange of the Series B Units for New AM Common Stock. During those presentations, Tudor Pickering provided, among other things: (i) a summary of the AMGP June 8 Proposal; (ii) a summary of the financial projections prepared by Antero Management, including their underlying assumptions; (iii) a preliminary valuation of the AM Common Units and New AM Common Stock, including a discounted distribution analysis, a peer group trading analysis, a contribution analysis, a premiums paid analysis, an accretion/dilution analysis and a precedent transactions analysis, in each case utilizing the financial projections prepared by Antero Management; (iv) an analysis of the proposed exchange ratio; (v) the impact of the New AM Common Stock to be issued in connection with the proposed settlement of the Series B Units on the AM Public Unitholders; and (vi) an analysis of the pro forma financial impact of the Potential Simplification to Antero Midstream and AMGP, both before and after giving effect to the taxes payable in connection with the Potential Simplification, utilizing the financial projections prepared by Antero Management. During the presentation, the AM Conflicts Committee asked, and representatives of Tudor Pickering answered, questions with respect to Tudor Pickering's preliminary financial analysis. Particular focus was placed on the taxable nature of the Potential Simplification, the expected taxes that would be payable by the AM Public Unitholders as a

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result of those transactions, adding a cash component to the merger consideration to offset expected taxes and protecting the AM Public Unitholders from the dilution caused by the proposed exchange of the Series B Units. During the presentation and with respect to each of the foregoing factors that was discussed, representatives of Tudor Pickering and the AM Conflicts Committee also discussed maintaining the status quo of Antero Midstream (which discussions concerning maintaining the status quo continued throughout the process leading to the AM Conflicts Committee granting "Special Approval" with respect to the Transactions). In addition, representatives of Gibson Dunn presented analyses regarding (x) the governance terms outlined in the AMGP June 8 Proposal, and (y) the required vote of AM Unitholders to approve the Potential Simplification, including whether the closing of the proposed transactions should be conditioned upon approval by a majority of the Disinterested AM Unitholders. In certain of those discussions, representatives of Gibson Dunn, including Gibson Dunn's tax specialist, provided analysis with respect to the expected taxes that would be payable by an average AM Public Unitholder as a result of the transaction.

        On June 12, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss the AMGP June 8 Proposal and next steps in the evaluation process. At the meeting, Baird reviewed with the AR Special Committee an implied premium analysis based on different time frames since the AR Special Committee had been formed. The AR Special Committee discussed the impact on completing a transaction that contemplated that the merger consideration would consist solely of shares of New AM Common Stock, without any cash component.

        On June 13, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. There was discussion with legal counsel regarding certain issues and items relating to the governance of New AM and terms remaining to be discussed and negotiated with the parties, Messrs. Rady and Warren, and the Sponsor Holders.

        On June 20, 2018, the AMGP Board held a meeting, with representatives of V&E and Goldman Sachs participating, as well as members of Antero Management. At the meeting, at the request of the AMGP Conflicts Committee, representatives of Goldman Sachs discussed illustrative dividend policies of New AM following the Potential Simplification, including certain implied distribution coverage metrics. Antero Management then presented the AMGP Board with an analysis of key financial metrics of recent comparable transactions.

        On June 21, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating. At the meeting, representatives of Baird discussed with the AR Special Committee its preliminary financial analysis of the AMGP June 8 Proposal, based on the financial projections received by Baird from Antero Management to date, and noting that certain items were subject to change pending certain diligence items requested by Baird. During the presentation, Baird presented, among other things, (a) a summary of the terms of the AMGP June 8 Proposal and initial takeaways, (b) current and pro forma ownership, and implied ownership by relative contribution, resulting from the AMGP June 8 Proposal, (c) an exchange ratio analysis, (d) precedent transaction analysis, (e) pro forma impact analysis and (f) a valuation analysis of the Series B Units.

        On June 22, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to consider the anticipated dividend policy of New AM, as discussed during the AMGP Board meeting and the future composition of the New AM Board.

        On June 27, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Representatives of Goldman Sachs discussed preliminary financial analyses regarding the potential settlement of the Series B Units in the Potential Simplification. There was discussion of certain terms of the Simplification Agreement that would be subject to negotiation for the Potential Simplification.

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        On June 28, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating. At the meeting, Sidley and Baird discussed certain tax consequences to Antero Resources based on the AMGP June 8 Proposal. After discussion, the AR Special Committee noted that the AMGP June 8 Proposal did not appear to compensate Antero Resources for the fact that, because the taxable nature of the proposed structure is an essential element of the Potential Simplification, Antero Resources would need to utilize approximately $3 billion of its federal income tax net operating losses ("NOLs") to offset taxable gain it would otherwise recognize in the transaction. The AR Special Committee also focused on the valuation ascribed to the Series B Units in the AMGP June 8 Proposal and the potential dilution to Antero Resources, as well as the impact of accelerating the vesting of all outstanding Series B Units, particularly the Series B Units held by Mr. Rady and Mr. Warren. The AR Special Committee requested that Sidley and Baird provide additional analyses of the impact on a Potential Simplification transaction of the Series B Units and instructed Sidley to reach out to V&E and Messrs. Rady and Warren to potentially schedule a discussion regarding those issues.

        On June 30, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn and Tudor Pickering to discuss supplemental financial analysis materials prepared by Tudor Pickering with respect to the Potential Simplification and the terms of a potential counteroffer to the AMGP June 8 Proposal. This supplemental analysis incorporated additional information received from Antero Management. The discussion focused on, among other things, certain tax implications of the AMGP June 8 Proposal, whether the interests of the Disinterested AM Unitholders may align with those of Antero Resources, including Antero Resources' potential interest in a cash consideration component, and the general advisability of undertaking the proposed transactions. After considering the analysis provided by Gibson Dunn, the AM Conflicts Committee discussed specific terms of a proposed counteroffer to AMGP, including the addition of a cash component to the merger consideration to offset expected taxes. Following further deliberations, the AM Conflicts Committee instructed Tudor Pickering to contact Baird to discuss the terms of a potential counteroffer and, to the extent that their interests aligned, to synthesize the financial terms of any such counteroffer by the AR Special Committee and the AM Conflicts Committee.

        On July 2, 2018, the compensation committee of the AR Board (the "Antero Resources Compensation Committee") held a meeting with the members of the AMGP Conflicts Committee, as well as Richard W. Connor, a member of the AR Board and AM Board, to discuss the Series B Units. Representatives of Goldman Sachs and Sidley also participated in the meeting. Mr. Clark serves as chairman of the Antero Resources Compensation Committee, and Mr. Hardesty serves as a member. Mr. Connor is not a member of the AR Special Committee or the Antero Resources Compensation Committee. At the meeting, Mr. Klimley and representatives of Goldman Sachs shared with the Antero Resources Compensation Committee the background behind the AMGP Conflicts Committee's Series B Unit negotiations with Mr. Rady and Mr. Warren. Later that day, the AR Special Committee met, with representatives of Baird and Sidley participating, and the AR Special Committee discussed the Series B Unit background that Mr. Clark and Mr. Hardesty had received as members of the Antero Resources Compensation Committee.

        On July 3, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating. At the meeting, Baird presented (a) a comparison of key metrics implied by the AMGP June 8 Proposal, (b) the impacts of modifying the exchange ratio to a higher level, (c) the impacts of adding a cash component to the transaction, (d) approaches to the Series B Unit valuation and (e) an illustrative counterproposal. The AR Special Committee continued to focus on the importance of a cash component to the merger consideration and the potential dilution to AM Unitholders once the Series B Units were exchanged and vested.

        On or about July 6, 2018, Mr. Klimley held several telephone conversations with Mr. Warren regarding Messrs. Rady's and Warren's views of the proposed governance and board composition of New AM. Messrs. Rady and Warren agreed to discuss with representatives of the Sponsor Holders

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designation rights with respect to the directors of New AM that would not be unaffiliated independent directors, which would consist of nine directors, including five independent directors not affiliated with Antero Resources, the Management Holders or the Sponsor Holders ("unaffiliated independent directors"), taking into account the ownership percentages of significant New AM Stockholders following the Potential Simplification.

        On July 8, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating. At the meeting, Baird presented supplemental discussion materials regarding certain pro forma impacts and the Series B Unit valuation proposed in the AMGP June 8 Proposal compared with the rights of the Series B Units in the absence of the Potential Simplification, as well as an update on the Water Earn-Out and its associated discount analysis.

        On July 9, 2018, representatives of Sidley, Baird, Tudor Pickering and Gibson Dunn discussed the AMGP June 8 Proposal, as well as the positions expected to be taken by the AR Special Committee and the AM Conflicts Committee in their respective counterproposals to the AMGP Conflicts Committee. After that call, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss the draft counterproposal from the AR Special Committee to the AMGP Conflicts Committee, including the feedback that the AR Special Committee's advisors had received from the AM Conflicts Committee's advisors regarding the AM Conflicts Committee's anticipated counterproposal. In this regard, the AR Special Committee discussed the benefits of adding an additional vesting feature to the shares of New AM Common Stock issuable in exchange for the tranche of Series B Units scheduled to vest December 31, 2019 (the "Final Unvested Tranche"). In order to better align the interests of Antero Management with Antero Resources' E&P operations, the vesting of the Final Unvested Tranche would be contingent upon Antero Resources' stand-alone E&P operations (i.e., without giving effect to cash flow attributable to any midstream operations) achieving positive free cash flow for the year ending December 31, 2019 ("E&P Free Cash Flow Vesting").

        On July 10, 2018, representatives from Sidley sent representatives of Gibson Dunn a draft of the AR Special Committee's proposed counteroffer to the AMGP June 8 Proposal. The terms of that proposed counteroffer included proposed merger consideration of 1.75 shares of New AM Common Stock and $4.00 in cash for each AM Common Unit, a proposed acceleration of Antero Midstream's potential earn-out payment obligations under the Water Asset Water Contribution Agreement (the "Revised Water Earn-Out Proposal") and the imposition of certain required vesting terms with respect to the New AM Common Stock to be issued in connection with the exchange of the Series B Units.

        Later on July 10, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn and Tudor Pickering to discuss the terms of the AR Special Committee's draft counterproposal. Tudor Pickering provided a summary of the AR Special Committee's proposed counterproposal as well as an updated analysis based on such proposal, including, among other things: (i) a revised valuation of the AM Common Units and New AM Common Stock, including a discounted distribution analysis, a peer group trading analysis, a contributions analysis, a premiums paid analysis and an accretion/dilution analysis; (ii) an analysis of the AR Special Committee's proposed exchange ratio; and (iii) an analysis of the pro forma financial impact of the AR Special Committee's proposed counterproposal to AM and AMGP, both before and after giving effect to the taxes payable in connection with the proposed counterproposal, utilizing the financial projections prepared by Antero Management. The AM Conflicts Committee instructed Tudor Pickering to advise Baird that (x) the AM Conflicts Committee was unwilling to support the Revised Water Earn-Out Proposal and (y) the AM Conflicts Committee proposed to condition the closing of the Potential Simplification on the approval of a majority of the Disinterested AM Unitholders.

        On July 12, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss the AR Special Committee's position and the AM Conflicts Committee's position in their respective counterproposals to AMGP. Following the discussion, the AR Special

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Committee approved the submission of the following counterproposal to the AMGP Conflicts Committee: (a) the vesting of the Final Unvested Tranche would be subject to E&P Free Cash Flow Vesting, (b) with respect to all shares of New AM Common Stock to be owned by Antero Resources, Antero Resources would be entitled to registration rights from New AM, comparable to the registration rights Antero Resources has with respect to its AM Common Units, (c) the Potential Simplification would not be conditioned upon a vote of AM Unitholders except for any vote required by the Antero Midstream Partnership Agreement or the Delaware Revised Uniform Limited Partnership Act (the "Delaware LP Act") and (d) the Water Earn-Out would accelerate, resulting in a $225 million payment from Antero Midstream to Antero Resources (representing a $25 million discount) (the "AR July 14 Counterproposal").

        On July 13, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Mr. Klimley reported on discussions held with Messrs. Rady and Warren and the Sponsor Holders regarding the governance of New AM, which would consist of the unaffiliated independent directors.

        On July 14, 2018, the AR Special Committee delivered the AR July 14 Counterproposal to the AMGP Conflicts Committee.

        On July 14, 2018, the AM Conflicts Committee held telephonic meetings with representatives of Tudor Pickering and Gibson Dunn to finalize the terms of the AM Conflicts Committee's proposed counterproposal to the AMGP June 8 Proposal. Following those meetings, Mr. Peters, on behalf of the AM Conflicts Committee, sent the AM Conflicts Committee's counterproposal to Mr. Klimley. In particular, the AM Conflicts Committee's counterproposal (the "AM July 14 Counterproposal") indicated the AM Conflicts Committee's willingness to negotiate definitive documentation with respect to the Potential Simplification on certain terms, including that (i) the merger consideration would consist of (x) 1.75 shares of New AM Common Stock and (y) $4.00 in cash for each AM Common Unit, (ii) all incentive distribution rights of Antero Midstream would be cancelled, (iii) the New AM Common Stock issued in exchange for the Series B Units in connection with the proposed transactions would be subject to the same vesting schedule as the Series B Units, (iv) AMGP would convert to a corporation with standard governance changes, (v) the dividend payouts at New AM would be increased to match the currently planned dividend targets at Antero Midstream for at least the first four quarterly periods following closing, and (vi) the closing of the Potential Simplification would be conditioned on approval by a majority of Disinterested AM Unitholders.

        On July 15, 2018, Mr. Klimley held a telephone call with all of the AMGP Conflicts Committee's advisors to discuss the terms of the AM July 14 Counterproposal and the AR July 14 Counterproposal.

        On July 17, 2018, Mr. Klimley held a telephone call with Mr. Warren to discuss the vesting of the Series B Units.

        On July 18, 2018, representatives of Sidley and Hunton Andrews Kurth discussed the AR July 14 Counterproposal, including certain corporate governance terms. Sidley explained that the AR Special Committee felt it was important to Antero Resources that it had positive free cash flow, and that it should not be diluted by the Series B Units. Additionally on July 18, 2018, representatives of Baird held a discussion with representatives of Goldman Sachs regarding the AR July 14 Counterproposal.

        Also on July 18, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. The AMGP Conflicts Committee discussed the AM July 14 Counterproposal and the AR July 14 Counterproposal. Representatives of Goldman Sachs reported on separate discussions held, at the direction of the AMGP Conflicts Committee, with the respective financial advisors to the AM Conflicts Committee and the AR Special Committee. Representatives of Goldman Sachs then discussed preliminary financial analyses regarding the Potential Simplification. After discussion, the AMGP Conflicts Committee agreed that it would make a counterproposal to the AM Conflicts Committee and

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the AR Special Committee that each outstanding AM Common Unit be exchanged for shares of New AM Common Stock at an exchange ratio of 1.65x, with any potential cash consideration to be negotiated as a reduction to the equity exchange ratio.

        On July 18, 2018, Antero Management provided the AR Special Committee, AM Conflicts Committee and AMGP Conflicts Committee with analysis of the implications of utilizing borrowings under Antero Midstream's revolving credit facility to fund the cash consideration proposed in the AR July 14 Counterproposal.

        On July 20, 2018, the AMGP Conflicts Committee held two telephonic meetings with all of its advisors to discuss the Series B Units and to refine and approve a letter to send as a counterproposal to the AM Conflicts Committee and the AR Special Committee with respect to the Potential Simplification.

        Later on July 20, 2018, the AMGP Conflicts Committee made a proposal to the AM Conflicts Committee and the AR Special Committee in a letter that provided, among other things, for each outstanding AM Common Unit to be exchanged for shares of New AM Common Stock at an exchange ratio of 1.65x, with any potential cash consideration to be negotiated as a reduction to the equity exchange ratio (the "AMGP July 20 Proposal"). The AMGP July 20 Proposal also provided that the shares of New AM Common Stock to be received in exchange for Series B Units would not be subject to time- or performance-based vesting and rejected negotiations of the Water Earn-Out in the context of the Potential Simplification. The AMGP July 20 Proposal also supported the AM Conflicts Committee's proposal to request approval of a majority of Disinterested AM Unitholders for the proposed transactions.

        On July 21, 2018 and July 24, 2018, the AM Conflicts Committee held telephonic meetings with representatives of Tudor Pickering and Gibson Dunn, including Gibson Dunn's tax specialist, to discuss the AMGP July 20 Proposal. During those meetings, representatives of Tudor Pickering presented Tudor Pickering's analysis of the financial terms of the AMGP July 20 Proposal, including the proposed merger consideration and the expected impact on the AM Public Unitholders after giving effect to the proposed settlement of the Series B Units. Tudor Pickering's analysis included, among other things: (i) a summary of the AMGP July 20 Proposal; (ii) a revised valuation of the AM Common Units and New AM Common Stock, including a discounted distribution analysis, a peer group trading analysis, a contributions analysis, a premiums paid analysis and an accretion/dilution analysis; (iii) an analysis of the proposed exchange ratio; and (iv) an analysis of the pro forma financial impact of the proposed transaction to Antero Midstream and AMGP, both before and after giving effect to the taxes payable in connection with the proposed transactions, utilizing the financial projections prepared by Antero Management. Discussions ensued with respect to the economic terms of a counterproposal to the AMGP July 20 Proposal as well as Tudor Pickering's discussions with Baird regarding the AR Special Committee's analysis of the proposed counterproposal. Based on the analysis prepared by Tudor Pickering, the AM Conflicts Committee agreed to propose merger consideration consisting of (x) 1.71 shares of New AM Common Stock and (y) $3.84 in cash for each AM Common Unit, and also agreed that the closing of the Potential Simplification would be conditioned on approval by a majority of Disinterested AM Unitholders and to reiterate the AM Conflicts Committee's expectation that the AM Public Unitholders would not realize a distribution cut as a result of the proposed transactions during the four quarters following the closing thereof. Following those meetings, on July 25, 2018, Mr. Peters delivered a counterproposal to the AMGP Conflicts Committee reflecting those proposed terms (the "AM July 25 Counterproposal").

        On July 22, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss the AR Special Committee's position on the AMGP July 20 Proposal. Representatives of Sidley provided the AR Special Committee a comparison of the various proposals that had been exchanged thus far. Representatives of Baird presented updated information regarding

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the premium reflected, as well as the pro forma impact, from the updated 1.65x exchange ratio provided in the AMGP July 20 Proposal. Following discussion, the AR Special Committee agreed that the following counterproposal should be delivered to the AMGP Conflicts Committee: (a) the Water Earn-Out Proposal would be withdrawn, (b) the merger consideration to be paid per AM Common Unit would consist of a combination of $3.84 in cash and 1.71 shares of New AM Common Stock, (c) the Series B Units would remain subject to the same vesting provisions and transfer restrictions to which the Series B Units are currently subject, (d) the Final Unvested Tranche would be subject to E&P Free Cash Flow Vesting, (e) distribution levels for current AM Unitholders must be maintained for at least the first four quarterly periods following closing, and those intentions must be clearly communicated to AM Unitholders and the investment community at the time the Potential Simplification is announced, (f) the organizational documents for New AM would contain corporate governance provisions customary for publicly traded Delaware corporations that do not have controlling stockholders, (g) with respect to the shares of New AM Common Stock to be owned by Antero Resources, Antero Resources would be entitled to registration rights from New AM, comparable to the registration rights Antero Resources has with respect to its AM Common Units and (h) the transaction would not be conditioned upon a vote of AM Unitholders except for any vote required by the Antero Midstream Partnership Agreement or the Delaware LP Act (the "AR July 25 Counterproposal").

        On July 25, 2018, the AR Special Committee delivered the AR July 25 Counterproposal to the AMGP Conflicts Committee.

        On July 26, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the AM July 25 Counterproposal and the AR July 25 Counterproposal. There was discussion of the terms of the two counterproposals, with a focus on the AM July 25 Counterproposal's proposed 1.71x exchange ratio, plus cash consideration of $3.84 for each AM Common Unit.

        On July 30, 2018, Mr. Klimley received an update from Mr. Warren on the status of the ongoing negotiations among Messrs. Warren and Rady and the Sponsor Holders regarding the governance and associated nomination rights for the directors of New AM.

        Later on July 30, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Mr. Klimley reported on his conversation with Mr. Warren regarding the ongoing negotiations with respect to governance rights for New AM. Mr. Klimley also reported that Mr. Warren provided an update in which Messrs. Warren and Rady and the Sponsor Holders reached a preliminary agreement regarding governance and associated nomination rights for directors constituting less than a majority of the New AM Board. The AMGP Conflicts Committee and its advisors then discussed the terms of response letters to send to the AM Conflicts Committee and the AR Special Committee. Representatives of Goldman Sachs reported on financial due diligence and discussions held with the financial advisor to the AM Conflicts Committee at the direction of the AMGP Conflicts Committee to understand the financial terms of its most recent counterproposal.

        On July 31, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to refine and approve the terms of counterproposal letters to send to the AM Conflicts Committee and the AR Special Committee. There was discussion with the AMGP Conflicts Committee's legal advisors regarding preliminary terms of the draft legal documentation for the Potential Simplification subject to negotiation by the parties, and legal aspects of the proposed fixed exchange ratio and cash consideration. The AMGP Conflicts Committee directed its legal advisors to provide comments to the draft legal documentation to V&E. Following discussion, the AMGP Conflicts Committee determined to respond to the AM Conflicts Committee and the AR Special Committee to propose that the respective financial advisors of each committee engage in discussions to clarify and synthesize each committee's proposals and perspectives.

        Later on July 31, 2018, the AMGP Conflicts Committee sent letters to the AM Conflicts Committee and the AR Special Committee proposing to have each committee's financial advisor

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engage in discussions to evaluate, among other things, the Potential Simplification, the exchange ratio and the potential for cash consideration.

        On August 1, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn and Tudor Pickering. During this meeting, Tudor Pickering discussed the AMGP Conflict Committee's response to the AM July 25 Counterproposal. Discussion ensued with respect to alternatives to the Potential Simplification, including maintaining the status quo. Following the discussions, the AM Conflicts Committee instructed Tudor Pickering and Gibson Dunn to follow up with Baird and Sidley to discuss the AMGP Conflict Committee's response.

        On August 1, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating, to discuss the AMGP Conflicts Committee's response to the AR July 25 Counterproposal. Baird prepared materials for the AR Special Committee to show the potential AMGP perspectives on the exchange ratio, including the cash versus equity component and a relative cash flow contribution analysis. Baird also discussed with the AR Special Committee expected Antero Midstream distributions, the coverage ratio adjustment that would be required in order for New AM to maintain distributions at currently expected levels on an exchange ratio-adjusted basis and estimated total cash to Antero Resources. The AR Special Committee discussed the AMGP Conflicts Committee's position that negotiations should be conducted with the AMGP Conflicts Committee only after the AM Conflicts Committee and AR Special Committee had resolved differences between themselves. After discussion, it was the consensus of the AR Special Committee that the AR Special Committee should be able to take positions that did not necessarily align with the AM Conflicts Committee, and that the most constructive method for resolving the outstanding issues would be for the AR Special Committee, the AM Conflicts Committee, the AMGP Conflicts Committee and the holders of a majority of the Series B Units to be involved in a single negotiation.

        On August 2, 2018, the AR Special Committee held a meeting, with representatives of Baird and Sidley participating. The AR Special Committee unanimously agreed to send a letter immediately back to the AMGP Conflicts Committee indicating the AR Special Committee's position that certain issues, including Series B Unit vesting proposals, board designation rights, as well as the exchange ratio and cash component, needed to be discussed and resolved in a manner equitable for all affected constituencies, and not just in a two-way negotiation. Immediately after the meeting, the AR Special Committee sent a letter to the AMGP Conflicts Committee. The AR Special Committee's letter also confirmed that it had authorized representatives of Baird to engage in discussions with representatives of Goldman Sachs.

        On August 3, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the letter received from the AR Special Committee on August 2, 2018. Representatives of Goldman Sachs discussed preliminary financial analyses of the Potential Simplification. Mr. Klimley also reported that the AMGP Conflicts Committee should expect to receive a draft term sheet from Mr. Warren regarding the agreement among Messrs. Warren and Rady and the Sponsor Holders related to the proposed governance and associated nomination rights for the directors of New AM.

        On the morning of August 7, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn and Tudor Pickering. During this meeting, Tudor Pickering reported on recent conversations with representatives of Goldman Sachs regarding discussions between the AMGP Conflicts Committee and the AM Conflicts Committee as to certain financial aspects of the Potential Simplification and the respective views of those two committees regarding those financial aspects. The group then discussed the proposed agenda for upcoming information sessions that were scheduled to be held in Denver, Colorado on August 9, 2018.

        On August 8, 2018, Antero Management circulated materials to the AR Board, the AM Board and the AMGP Board for an informational session with the Boards to be held on August 9, 2018. These

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materials included, among other things, an outline summarizing governance terms proposed by the AR Special Committee and a related presentation. The materials also included a straw-man presentation of how a potential transaction would be rolled out to equityholders and the investment community at large, with economic terms omitted from the materials.

        Later on August 8, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss proposed governance of New AM. There was also discussion of recent financial due diligence and Goldman Sachs' discussions at the direction of the AMGP Conflicts Committee with the financial advisors to the AM Conflicts Committee regarding the tax analysis included in the AM Conflicts Committee's most recent proposal.

        On August 9, 2018, members of Antero Management, the AR Board (including the AR Special Committee) and representatives of Sidley, Baird, V&E, J.P. Morgan, Hunton Andrews Kurth and Richards Layton held an information session in Denver, Colorado. During the session, representatives of Richards Layton presented an overview of the governance rights to be provided to the holders of New AM Common Stock pursuant to the summary governance terms proposed by the AMGP Conflicts Committee. Richards Layton emphasized the AMGP Conflicts Committee's position that a majority of the New AM Board should consist of unaffiliated independent directors and that AMGP's conversion to a corporation whose directors would be elected by New AM Stockholders was essential to the AMGP Conflicts Committee's evaluation of the Potential Simplification. Richards Layton also noted that, if New AM were to convert to a corporation, its directors would have corporate fiduciary duties. Richards Layton then discussed certain proposed New AM Board nomination rights that were proposed to be granted to Antero Resources, Messrs. Rady and Warren and the Sponsor Holders pursuant to a stockholders' agreement to be entered into in connection with the Potential Simplification. Following this discussion, the representatives of Richards Layton and Hunton Andrews Kurth departed the meeting and J.P. Morgan presented its views regarding the general benefits of, and the trading implications and leverage and credit considerations for the Potential Simplification. J.P. Morgan affirmed its view that the Potential Simplification was the preferable structural alternative for addressing stockholder concerns and maximizing growth. Mr. Warren then explained the Management Holders' position regarding the proposed settlement of the Series B Units and the Series B Holders' valuation of those Series B Units.

        On the afternoon of August 9, 2018, members of Antero Management, the AM Board (including the AM Conflicts Committee) and representatives of Gibson Dunn, Tudor Pickering, V&E, Morgan Stanley, Hunton Andrews Kurth and Richards Layton held an information session in Denver, Colorado. During the session, representatives of Richards Layton presented an overview of the governance rights to be provided to the holders of New AM Common Stock pursuant to the summary governance terms proposed by the AR Special Committee. Richards Layton emphasized the AMGP Conflicts Committee's position that a majority of the New AM Board should consist of unaffiliated independent directors and that AMGP's conversion to a corporation whose directors would be elected by New AM Stockholders was essential to the AMGP Conflicts Committee's evaluation of the Potential Simplification. Richards Layton also noted that, if New AM were to convert to a corporation, its directors would have corporate fiduciary duties. Richards Layton then discussed certain proposed New AM Board nomination rights that were proposed to be granted to Antero Resources, Messrs. Rady and Warren and the Sponsor Holders pursuant to a stockholders' agreement to be entered into in connection with the Potential Simplification. Following this discussion, the representatives of Richards Layton and Hunton Andrews Kurth departed the meeting and Morgan Stanley presented its views regarding the rationale for, and the trading implications and leverage and credit considerations for the Potential Simplification. Morgan Stanley affirmed its conclusion that the Potential Simplification appeared to be the optimal restructuring strategy given current market conditions, with a particular emphasis on elimination of the incentive distribution rights.

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        On August 9, 2018, the AMGP Conflicts Committee's legal advisors participated in separate calls with the AR Board and the AM Board to discuss the terms for settling the Series B Units and the proposals regarding board representation and corporate governance.

        On August 10, 2018, following the discussions between the AMGP Conflicts Committee, AR Board and AM Board, V&E provided initial drafts of the Simplification Agreement, the AMGP Voting Agreement, the AR Voting Agreement and the IDR Holdings LLCA Amendment to Sidley and Gibson Dunn for review on behalf of the AR Special Committee and AM Conflicts Committee, respectively, which drafts reflected V&E's understanding of the terms of the AMGP Conflicts Committee's most recent proposal, as well as input from Hunton Andrews Kurth and Richards Layton on behalf of the AMGP Conflicts Committee.

        On August 11, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the status of negotiations of the Potential Simplification. After discussion, the AMGP Conflicts Committee directed its advisors to prepare a counterproposal to the AM Conflicts Committee providing for each outstanding AM Common Unit to be exchanged for shares of New AM Common Stock at an exchange ratio of 1.7x, with any potential cash consideration to be negotiated as a reduction to the equity exchange ratio. The AMGP Conflicts Committee also considered financial due diligence and information from Antero Management regarding cash requirements and expected views of rating agencies. After further consideration, the AMGP Conflicts Committee supported cash merger consideration of $3.00 per AM Common Unit. The AMGP Conflicts Committee's counterproposal was sent to the AM Committee and the AR Special Committee on August 12, 2018 (the "AMGP August 12 Proposal")

        On August 12, 2018, the AR Special Committee and representatives of Baird and Sidley had a call to discuss the AMGP August 12 Proposal in preparation for planned in-person negotiations to take place in Denver, Colorado the following week, which negotiations the AR Special Committee expected and hoped would involve representatives of the AR Special Committee, AMGP Conflicts Committee, AM Conflicts Committee and the Management Holders (on behalf of all Series B Holders). Additionally, on August 12, 2018, the AR Special Committee approved the engagement of Potter Anderson & Corroon LLP ("Potter Anderson") as Delaware counsel to the AR Special Committee.

        On August 13, 2018, the AM Conflicts Committee held a telephonic meeting, and on August 14, 2018, the AM Conflicts Committee held a meeting, in each case, with representatives of Tudor Pickering and Gibson Dunn to discuss the AMGP August 12 Proposal and scheduled August 14, 2018 negotiations with the AR Special Committee and the AMGP Conflicts Committee and their respective advisors. During those meetings, representatives of Tudor Pickering presented Tudor Pickering's analysis of the financial terms of the AMGP August 12 Proposal, including the proposed merger consideration and the expected impact on the AM Public Unitholders after giving effect to the Series B Exchange. Tudor Pickering's analysis included, among other things: (i) updates to the materials from the analysis that had been provided to the AM Conflicts Committee with respect to the prior proposal made by the AMGP Conflicts Committee; (ii) an after-tax distribution model for the average holder of AM Common Units; (iii) an analysis with respect to the valuation of the AM Common Units and New AM Common Stock based on the AMGP August 12 Proposal, including a discounted distribution analysis, a peer group trading analysis, a contribution analysis and a precedent transactions analysis; and (iv) the impact of the proposed transactions on the leverage profile and yield of New AM, in each case utilizing both the base case and downside financial projections prepared by Antero Management. The group also noted recent discussions with the AR Special Committee in which the AR Special Committee's financial and legal advisors noted that the AR Special Committee will not require the Water Earn-Out Proposal in connection with its approval of the Potential Simplification.

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        On August 14, 2018, members and financial and legal advisors of the AM Conflicts Committee, AR Special Committee and AMGP Conflicts Committee held a series of meetings in Denver without the Management Holders present to discuss open issues.

        Also on August 14, 2018, members of the AM Conflicts Committee and AR Special Committee, together with their financial and legal advisors, held a meeting. During that meeting, the two committees agreed to propose to the AMGP Conflicts Committee that the merger consideration per AM Common Unit would consist of $3.00 in cash plus 1.71 shares of New AM Common Stock (the "AM August 14 Counterproposal"). During that discussion, the AR Special Committee agreed to support the AM Conflicts Committee's request that the Potential Simplification be conditioned upon the receipt of Disinterested AM Unitholder Approval. The AM Conflicts Committee agreed to support the AR Special Committee's request that the governance term sheet be modified to provide that (i) a majority of the New AM Board's directors would at all times be unaffiliated independent directors and (ii) the share ownership thresholds required to be satisfied in order to have director designation rights would be the same for Antero Resources, the Sponsor Holders, and Mr. Rady and Mr. Warren. The AR Special Committee also agreed not to continue to pursue the E&P Free Cash Flow Vesting of the Series B Units.

        Mr. Klimley then joined the meeting, together with representatives from Goldman Sachs and a representative of Hunton Andrews Kurth. After receiving the joint proposal from the AR Special Committee and the AM Conflicts Committee, Mr. Klimley responded that the AMGP Conflicts Committee believed that its latest proposal of 1.7x was a reasonable exchange ratio and that the AM Conflicts Committee and the AR Special Committee were not giving enough credit to the improved governance that would result from the fact that New AM would be a Delaware corporation. Mr. Klimley said that the AMGP Conflicts Committee was also concerned about the increased leverage that would result from paying cash in the Potential Simplification. Mr. Klimley emphasized that any cash that would be paid as consideration would reduce the number of shares of New AM Common Stock to be received in the merger. Mr. Klimley also noted that maintaining the vesting of the Series B Units or reducing the number of shares of New AM Common Stock that would be exchanged for Series B Units would need to be addressed with the Series B Holders.

        The AM Conflicts Committee responded that many of the AM Public Unitholders would be required to pay cash taxes as a result of the transaction. The AR Special Committee responded that the AMGP Conflicts Committee was not compensating Antero Resources in the exchange ratio for its use of approximately $3 billion of its NOLs to offset taxable gain it would otherwise recognize in the transaction. The AR Special Committee also noted that the payment to Antero Resources of a meaningful amount of cash in the Potential Simplification was a priority for the AR Special Committee. Both the AM Conflicts Committee and the AR Special Committee continued to stress the importance of maintaining the vesting and forfeiture provisions applicable to the Series B Units. They also emphasized that the exchange ratio should be higher to compensate for the dilutive impact of the issuance of shares of New AM Common Stock in exchange for Series B Units.

        After a lengthy discussion among the committee members without the presence of legal or financial advisors, Mr. Klimley proposed (i) an exchange ratio of 1.71 shares of New AM Common Stock for each AM Common Unit and (ii) a cash election feature that would permit each AM Unitholder (including Antero Resources) to elect to receive consideration that includes up to $3.00 in cash per AM Common Unit (with a corresponding reduction in the number of shares of New AM Common Stock to be received by the AM Unitholders). The AM Conflicts Committee and AR Special Committee responded that they were not willing to support Mr. Klimley's proposal, and the meetings ended without a resolution of the outstanding issues.

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        Immediately following the conclusion of the August 14 meeting, Mr. Klimley, representatives from Goldman Sachs and a representative from Hunton Andrews Kurth updated Messrs. Rady and Warren on the lack of progress on resolution of the outstanding issues.

        On August 15, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the in-person meeting that occurred on the preceding day among the AMGP Conflicts Committee, the AM Conflicts Committee and the AR Special Committee. The AMGP Conflicts Committee and its advisors discussed proposed terms, potential alternatives for the vesting of the Series B Units, and various governance proposals under negotiation among the parties regarding the composition of the New AM Board.

        On August 16, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Also in attendance, by invitation of the AMGP Conflicts Committee, were Messrs. Warren and Rady to discuss their views, in their capacities as Series B Holders and as Antero Management, as applicable, regarding the Series B Units and other proposed terms of the Potential Simplification, including: (i) potential exchange ratios for the Potential Simplification, (ii) their agreement to accept a continued vesting schedule of the Series B Units for the new shares of New AM Common Stock they receive (as opposed to the acceleration of vesting in connection with the settlement of the Series B Units as previously proposed by the Series B Holders), (iii) a proposal to continue the limited partnership entity structure and governance at AMGP post-transaction as opposed to changing to a corporate-style governance structure and (iv) a proposal that the New AM Board include a majority independent board appointed by the equity owners of AMGP GP. After Messrs. Warren and Rady left the meeting, the meeting continued with only the AMGP Conflicts Committee and all of its advisors in attendance. Representatives of Goldman Sachs reported on their discussions with Tudor Pickering and preliminary financial analyses of the counterproposal received from the AM Conflicts Committee and AR Special Committee at the in-person meeting on August 14, 2018.

        On August 17, 2018, Mr. Klimley and Mr. Warren discussed the Potential Simplification and the Management Holders' views that New AM should continue as a limited partnership as opposed to a C-corporation.

        On August 20, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the status of proposals and counterproposals, including the governance structure of New AM and the Management Holders' views on the governance structure of New AM. There was discussion of proposed terms and conditions, preliminary financial analyses and potential counterproposals to make to the AM Conflicts Committee. After discussion, the AMGP Conflicts Committee determined to make a counterproposal to the AM Conflicts Committee that provided for each outstanding AM Common Unit to be exchanged for shares of New AM Common Stock at an exchange ratio of 1.616x, plus cash consideration of $3.00 per AM Common Unit, which represented an aggregate exchange ratio of approximately 1.775x. The AMGP Conflicts Committee proposal assumed that New AM would have a corporate-style governance structure.

        On August 20, 2018, Mr. Klimley contacted Mr. Peters and conveyed the AMGP Conflicts Committee's proposal. At the direction of the AMGP Conflicts Committee, representatives of Goldman Sachs also conveyed the AMGP Conflicts Committee's proposal to Tudor Pickering. The AM Conflicts Committee indicated that it would not accept the AMGP Conflicts Committee's counterproposal and was not willing to revise the AM August 14 Counterproposal.

        Later on August 20, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss an update from Mr. Klimley. Mr. Klimley reported that he delivered the AMGP Conflicts Committee's counterproposal to the AM Conflicts Committee. The AMGP Conflicts Committee discussed the status of the Potential Simplification and concluded that it would not make any counterproposal to the AM Conflicts Committee at this time.

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        On August 21, 2018, representatives of Sidley discussed with representatives of Gibson Dunn the status of current negotiations between the AMGP Conflicts Committee and the AM Conflicts Committee. However, no substantive proposals were exchanged. Additionally, Sidley had a call with V&E to discuss the Series B Units and mechanics of vesting and forfeitures. Sidley suggested a meeting with the AR Special Committee in order to confirm that all parties had the same information.

        On August 22, 2018, there were several calls between Mr. Klimley and Mr. Warren regarding the status of the discussions between Mr. Warren and Peter Kagan, an AMGP Sponsor Director, concerning board representation and corporate governance.

        Between August 22, 2018 and August 27, 2018, representatives of the AMGP Conflicts Committee, the AR Special Committee and the Series B Holders continued to discuss potential ways to effect the Potential Simplification.

        On August 27, 2018, Mr. Clark had a call with Mr. Klimley in an attempt to move the negotiations forward. Mr. Klimley had proposed to obtain the AR Special Committee's support for a modified proposal, to be followed by obtaining support from the Series B Holders, and then followed by seeking support from the AM Conflicts Committee. Later on August 27, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. In addition, present by invitation from the AMGP Conflicts Committee were members of the AR Special Committee, representatives of Baird and representatives of Sidley. After discussion, the AR Special Committee agreed to send an email to the AMGP Conflicts Committee, confirming its support for the AMGP Conflicts Committee's modified proposal, as follows: (i) an exchange ratio of 1.775 shares of New AM Common Stock for each AM Common Unit, including $3.00 per share in cash, (ii) a cash election option for AM Unitholders, (iii) a special cash distribution to AM Public Unitholders of $0.415 per AM Common Unit immediately prior to closing, (iv) the Series B Units would be exchanged for a total of 18 million shares of New AM Common Stock, a reduction from the AMGP Conflicts Committee's previously-proposed 18.5 million shares, (v) the Series B Units for Mr. Rady, Mr. Warren and Michael N. Kennedy, Chief Financial Officer and Senior Vice President of Finance of AMGP GP, would continue to vest in accordance with their time-based terms, but the Series B Units for the other Series B Holders would vest immediately upon closing, (vi) distributions would be maintained for all AM Unitholders for four calendar quarters following closing, (vii) customary registration rights for Antero Resources, (viii) a classified New AM Board, with a majority of unaffiliated independent directors and (ix) designation rights for Antero Resources with respect to the New AM Board (the "AMGP August 27 Proposal").

        Later on August 27, 2018, Mr. Klimley delivered the AMGP August 27 Proposal to Messrs. Rady and Warren. In response, Messrs. Rady and Warren would not agree to reduce the exchange of the Series B Units from 18.5 million to 18 million shares of New AM Common Stock, and instead offered to extend the vesting schedule of unvested Series B Units by approximately nine months.

        Later on August 27, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Mr. Klimley reported on his conversations with Mr. Clark and Messrs. Rady and Warren. There was further discussion with respect to the potential accrual of distributions, alternative vesting schedules for the Series B Units and potential extended vesting schedules without the accrual of distributions. It was agreed that, instead of the extended vesting schedule, the AMGP Conflicts Committee would propose that unvested Series B Units not accrue distributions during calendar year 2019, which represented a reduction in economic value of approximately $8 million to the Series B Holders. Mr. Klimley agreed to convey this proposal to the AR Special Committee and Messrs. Rady and Warren.

        On August 28, 2018, the AR Special Committee convened another meeting after Mr. Klimley sent Mr. Clark an email with updated terms, which reflected the feedback he had received in his discussions with Mr. Rady and Mr. Warren about the AMGP August 27 Proposal. Mr. Klimley's revised proposal provided that, in exchange for maintaining the number of shares of New AM Common Stock to be

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exchanged for the Series B Units at 18.5 million shares, (i) the new shares of New AM Common Stock issued in exchange for the Series B Units would maintain the existing vesting schedule for all parties, and (ii) the Final Unvested Tranche would not be eligible for dividends during 2019 (the "AMGP August 28 Proposal"). Mr. Klimley requested the AR Special Committee's feedback in order to discuss the modified terms with Mr. Rady and Mr. Warren. The AR Special Committee then convened a meeting, and Baird presented the AR Special Committee with a summary comparison of the proposed dividend waiver with the proposed reduction in shares of New AM Common Stock to be issued upon exchange of the Series B Units.

        On the morning of August 29, 2018, the AR Special Committee met again to discuss the AMGP August 28 Proposal. Mr. Clark provided the AR Special Committee a further update on a second phone call he had had with Mr. Klimley, which provided some additional context regarding the AMGP Conflicts Committee's position on the vesting schedule and the dividend waiver with respect to the Series B Units. The AR Special Committee deliberated over that call and another one later that afternoon, and unanimously determined to support the AMGP August 28 Proposal. In reaching this determination, the AR Special Committee focused on the progress made with respect to the cash component of the exchange ratio and vesting schedule of the Series B Units in its determination that the transaction would in the best interests of Antero Resources and its unaffiliated stockholders. Shortly after the meeting, representatives of Sidley sent the AMGP Conflicts Committee an email to that effect.

        Later on August 29, 2018, V&E distributed a revised draft of the governance term sheet, which reflected V&E's understanding of the prior negotiations among the three committees, as well as additional comments from the Management Holders. Representatives of Sidley had a phone call with representatives of V&E to better understand the Management Holders' position on governance. The next morning, representatives of Sidley distributed to the AR Special Committee Sidley's recommendation on the governance term sheet and a summary of the conversation held with V&E.

        On August 29, 2018, Messrs. Rady and Warren contacted Mr. Klimley and agreed to the AMGP Conflicts Committee's proposal that the Final Unvested Tranche not accrue distributions during calendar year 2019, which would reduce cash payable to the Series B Holders by approximately $8 million. Messrs. Rady and Warren also indicated that they and the Sponsor Holders were generally in agreement regarding C-corporation governance for the post-transaction company.

        Later on August 29, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Mr. Klimley reported on conversations that he had with Messrs. Rady and Warren regarding the settlement of the Series B Units and the AR Special Committee regarding the Potential Simplification.

        On August 30, 2018, Mr. Klimley transmitted a presentation to the AM Conflicts Committee reflecting the AMGP August 28 Proposal, and the AMGP Conflicts Committee held a telephonic meeting with the AM Conflicts Committee to discuss the terms contained in that presentation.

        On August 31, 2018, representatives of Antero Management, V&E, Hunton Andrews Kurth, Gibson Dunn, Tudor Pickering and Goldman Sachs held a telephonic meeting to discuss the anticipated tax treatment of the AMGP August 28 Proposal.

        On August 31, 2018, representatives of Sidley discussed the latest draft of the governance term sheet with representatives of Gibson Dunn. The AR Special Committee held a meeting later that afternoon to discuss Gibson Dunn's and the AM Conflicts Committee's thoughts on the governance term sheet and directed Sidley to send a revised draft of the governance term sheet to V&E and the AMGP Conflicts Committee, which Sidley did immediately following that call. Later that afternoon, Mr. Clark received an email from Mr. Warren regarding the revised governance term sheet, in an attempt to understand the response and position of the AR Special Committee.

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        Representatives of Sidley discussed the revised governance term sheet with representatives of V&E on the morning of September 1, 2018, resulting in Sidley proposing an updated governance term sheet later that afternoon at the request of the AR Special Committee. That evening, V&E sent Sidley an email letting them and the AR Special Committee know that Mr. Rady and Mr. Warren were generally signed off on the governance term sheet.

        On the morning of September 2, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn and Tudor Pickering. The group discussed the 1.775x exchange ratio and $0.415 special cash distribution included in the AMGP August 28 Proposal and Tudor Pickering presented materials related thereto. Representatives of Tudor Pickering presented Tudor Pickering's analysis of the financial terms of the AMGP August 28 Proposal, including the Series B Exchange and the expected dilutive impact of that exchange on the AM Public Unitholders. Tudor Pickering's analysis also included, among other things: (i) the after-tax distribution model for the average AM Public Unitholder; (ii) updates to the materials from the analysis that had been provided to the AM Conflicts Committee with respect to the AMGP Conflicts Committee's prior proposal; (iii) an analysis with respect to the valuation of the AM Common Units and New AM Common Stock based on the AMGP August 28 Proposal, including a discounted distribution analysis, a contribution analysis, a peer group trading analysis and a precedent transactions analysis; (iv) an analysis of the proposed exchange ratio; and (v) an analysis of the exchange of different amounts of New AM Common Stock with respect to the proposed settlement of Series B Units and the dilutive effect of those amounts on the AM Public Unitholders. Based on Tudor Pickering's financial analysis, the AM Conflicts Committee determined that, based on the number of shares of New AM Common Stock proposed to be issued in the proposed settlement of the Series B Units, an exchange ratio of 1.85x was appropriate (with a portion of that consideration to be paid in the form of cash). The AM Conflicts Committee also noted that a lower exchange ratio may be appropriate in the event that the AMGP Conflicts Committee and Series B Holders agreed to reduce the dilutive impact of the proposed exchange of the Series B Units on the AM Public Unitholders. Following the meeting, Mr. Peters orally communicated the position of the AM Conflicts Committee to Mr. Klimley.

        Also on September 2, 2018, Mr. Klimley received a telephonic response in which the AM Conflicts Committee rejected the AMGP August 28 Proposal and offered: (i) the exchange of each outstanding AM Common Unit for shares in New AM at an aggregate exchange ratio of 1.85x or (ii) the exchange of each outstanding AM Common Unit for shares in New AM at an exchange ratio of 1.775x plus a one-time cash distribution of $0.415 to the AM Public Unitholders, which represented an exchange ratio of approximately 1.80x in the aggregate, and a reduction in the exchange of Series B Units from 18.5 million to 13.5 million shares of New AM Common Stock (together, the "AM September 2 Counterproposal"). Mr. Klimley also had discussions with Mr. Warren to convey the proposal that the settlement of the Series B Units be reduced, which option was declined by Mr. Warren, and to consider alternative structures for the Potential Simplification.

        On September 3, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Mr. Klimley reported that the AM Conflicts Committee rejected the AMGP August 28 Proposal and described the AM September 2 Counterproposal. The AMGP Conflicts Committee determined that it would not make a counterproposal at this time.

        On September 13, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. There was discussion with respect to the potential benefits of, and rationale for, the Potential Simplification from the various perspectives of AMGP and the Disinterested AMGP Shareholders, Antero Midstream, Antero Resources, the Series B Holders and the Management Holders. Following discussion, the AMGP Conflicts Committee agreed that it would continue to support the AMGP August 28 Proposal and would not offer additional consideration to other parties. It was further agreed that the AMGP Conflicts Committee would send a letter to the AMGP Board, the AM Conflicts

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Committee, the AR Special Committee and Antero Management stating the AMGP Conflicts Committee's continued support for the AMGP August 28 Proposal.

        On September 14, 2018, the AMGP Conflicts Committee delivered a letter to the AMGP Board, the AM Conflicts Committee, the AR Special Committee and the Management Holders expressing the AMGP Conflicts Committee's continued support for the AMGP August 28 Proposal (the "AMGP September 14 Letter").

        On September 15, 2018, Mr. Clark relayed to the AR Special Committee a telephone call he received from Mr. Kagan promoting a concept of a four-way compromise between the parties with the goal of ultimately coming to an agreement that all parties could approve. Mr. Kagan had suggested that the financial advisors of each of the AR Special Committee, the AM Conflicts Committee, and the AMGP Conflicts Committee meet with Citigroup Global Markets Inc. ("Citi"), financial advisor to the Sponsor Holders, in order to discuss potential resolutions to the apparent impasse.

        Throughout the next few days, the financial advisors of each of the three committees held separate discussions with Citi to explore possible compromises. On September 16, 2018, the AM Conflicts Committee held telephonic meetings with representatives of Tudor Pickering and Gibson Dunn to discuss the September 14, 2018 letter from the AMGP Conflicts Committee rejecting the AM September 2 Proposal. At this meeting, it was noted that the Sponsor Holders had engaged Citi as a financial advisor in connection with the Potential Simplification.

        On September 17, 2018, the AR Special Committee met, with representatives of Sidley and Baird participating, in order for Baird to present a summary of an illustrative framework previously conveyed by Citi on behalf of the Sponsor Holders to Baird for bridging the gap regarding the remaining open financial points, primarily related to the allocation of New AM Common Stock in connection with the Potential Simplification. Under this illustrative framework, the AM Public Unitholders, AR, AMGP and the Series B Holders would each effectively bear 25% of the approximately 4.5 million share gap between the AMGP Conflict Committee's most recent proposal and the AM Conflict Committee's most recent proposal. Baird shared a potential updated exchange ratio and potential decrease in the number of shares of New AM Common Stock that the Series B Unitholders would be entitled to receive upon the closing of the Potential Simplification, as well as a pro forma impact analysis. The next day, on September 18, 2018, the AR Special Committee sent a revised term sheet to each of the AMGP Conflicts Committee and the AM Conflicts Committee and their respective advisors regarding the AR Special Committee's understanding of the proposed terms. Additionally, on this date, Citi, at the request of the Sponsor Holders, relayed to representatives of the AMGP Conflicts Committee, the AM Conflicts Committee and the AR Conflicts Committee a summary of the framework previously conveyed by Citi on behalf of the Sponsor Holders to Baird.

        Also on September 18, 2018, the AM Conflicts Committee sent a response to the AMGP September 14 Letter (the "AM September 18 Letter"). The AM September 18 Letter retracted the AM September 2 Proposal, noted that given the current market exchange ratios and in order to protect the Disinterested AM Unitholders from dilution from the settlement of the Series B Units, the appropriate exchange ratio should be from 1.815x to 1.878x. The AM Conflicts Committee also requested an update to the projections provided by Antero Management to the AM Conflicts Committee.

        On September 21, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. The AMGP Conflicts Committee and all of its advisors discussed various responses to its most recent letter, including the letter from the AM Conflicts Committee (i) withdrawing the AM September 2 Proposal and (ii) requesting that Antero Management confirm its financial projections. It was also noted that Mr. Kagan had indicated that the Sponsor Holders were working on developing structural alternatives for the Potential Simplification. Mr. Klimley then explained that the Series B Holders responded with a proposal that would reduce the settlement of the Series B Units from 18.5 million to 17.354 million shares of New AM Common Stock. There was discussion of the

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settlement of the Series B Units, the merits and economics of the most recent proposal relating to the settlement of the Series B Units, and potential changes to the proposal relating to the Series B Units. It was then agreed that the AMGP Conflicts Committee would send a letter to the AM Conflicts Committee and the AR Special Committee reflecting a reduction in the settlement of the Series B Units from 18.5 million to 17.354 million shares of New AM Common Stock generally consistent with the proposal relating to the settlement of the Series B Units made by the Management Holders and increasing the merger consideration payable to the AM Public Unitholders.

        Later on September 21, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. In addition, participating by invitation of the AMGP Conflicts Committee, were Messrs. Rady and Warren, as well as Brendan Krueger, Vice President of Finance of Antero Resources. The AMGP Conflicts Committee asked Messrs. Rady and Warren to provide a letter confirming that the settlement of the Series B Units would be reduced to 17.354 million shares of New AM Common Stock. The AMGP Conflicts Committee also asked that Antero Management confirm their financial forecasts were up-to-date and that there had been no material changes, and such confirmation was provided subsequently by Antero Management.

        Later on September 21, 2018, Messrs. Rady and Warren provided a letter confirming that the settlement of the Series B Units would be reduced to 17.354 million shares of New AM Common Stock.

        On September 22, 2018, the AMGP Conflicts Committee sent a letter to the AM Conflicts Committee and the AR Special Committee indicating that Messrs. Rady and Warren agreed to reduce the settlement of the Series B Units to 17.354 million shares of New AM Common Stock. The AMGP Conflicts Committee letter also proposed (1) the exchange of each outstanding AM Common Unit held by the AM Public Unitholders for shares of New AM Common Stock at an exchange ratio of 1.6350x plus cash consideration of $3.00 for each AM Common Unit, subject to election and proration, (2) a one-time cash distribution of $0.415 per AM Common Unit to the AM Public Unitholders, (3) the exchange of each outstanding AM Common Unit held by the Antero Resources for shares in New AM at an exchange ratio of 1.6023x plus cash consideration of $3.00 for each AM Common Unit, subject to election and proration, and (4) no corresponding cash distribution to Antero Resources in respect of its AM Common Units (the "AMGP September 22 Proposal").

        On September 23, 2018, the AR Special Committee held a meeting with Sidley and Baird to discuss certain financial issues, including the components of the total Merger Consideration under the AMGP September 22 Proposal, focusing on the ability of maintaining the distribution for AM Unitholders for the four quarters following the proposed transaction. During the meeting the AR Special Committee discussed the rationale for the AM Public Unitholders receiving a higher exchange ratio and a one-time cash distribution of $0.415 per AM Common Unit.

        On September 25, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the AMGP September 22 Proposal sent to the AM Conflicts Committee and the AR Special Committee. Mr. Klimley reported that the AR Special Committee had met to discuss the AMGP September 22 Proposal, and that the AR Special Committee was supportive of the current proposal as long as the AM Conflicts Committee would also support the proposal. The AMGP Conflicts Committee and its advisors discussed the settlement of the Series B Units, including the mechanics to exchange the Series B Units.

        Later on September 25, 2018, the AMGP Conflicts Committee met with the other non-management members of the AMGP Board, the AM Board and the AR Board to discuss the Potential Simplification, including with respect to the proposed exchange ratios, the settlement of the Series B Units and the request to confirm there had been no material changes to the financial forecasts of Antero Management previously provided to the AMGP Conflicts Committee.

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        On September 26, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. Mr. Klimley reported on the conversations that occurred at the meeting of the AMGP Conflicts Committee and the other non-management members of the AMGP Board, the AM Board and the AR Board. Discussion ensued regarding the status of due diligence and draft legal documentation for the Potential Simplification.

        Throughout the weeks of September 24, 2018 and October 1, 2018, V&E distributed drafts of the transaction documents, including the Simplification Agreement, the registration rights agreement, the Stockholders' Agreement, the IDR Holdings LLCA Amendment, the AMGP Voting Agreement, the AR Voting Agreement, the New AM certificate of incorporation and bylaws, the Certificate of Designation and various other transaction documents (collectively, the "Transaction Documents"), which each of the AMGP Conflicts Committee, the AM Conflicts Committee and the AR Special Committee reviewed and revised with the advice and guidance of their respective advisors.

        During this time, V&E also distributed drafts of the Transaction Documents to each of (i) Kirkland & Ellis LLP, outside corporate counsel for the Sponsor Holders affiliated with Warburg Pincus LLC ("Kirkland & Ellis"), (ii) Thompson & Knight LLP, outside corporate counsel for the Sponsor Holders affiliated with Yorktown Partners LLC ("Thompson Knight"), and (iii) Abrams & Bayliss LLP, outside corporate counsel for Messrs. Rady and Warren ("Abrams & Bayliss" and, together with each of Sidley, Gibson Dunn, Hunton Andrews Kurth, Richards Layton, Potter Anderson, Kirkland & Ellis and Thompson Knight, the "Outside Legal Advisors"). Throughout this time, each of the Sponsor Holders and Messrs. Rady and Warren reviewed and revised the Transaction Documents with the advice and guidance of their respective Outside Legal Advisors.

        On September 27, 2018 and September 29, 2018, the AM Conflicts Committee held telephonic meetings with representatives of Tudor Pickering and Gibson Dunn to discuss the AMGP September 22 Proposal. In particular, the parties discussed materials prepared by Gibson Dunn, including information regarding change in recommendation and break fee provisions found in precedent transactions, and materials prepared by Tudor Pickering describing the effects of the increased consideration to the AM Public Unitholders and the reduction in the number of shares of New AM Common Stock to be issued in the proposed settlement of the Series B Units and outlining potential consideration mechanisms that could protect AM Unitholders from potential uncertainty regarding how the market would view New AM given the proposed terms of the Potential Simplification. In addition, Tudor Pickering discussed updates to its materials to reflect the terms proposed in the AMGP September 22 Proposal. Upon the completion of its review of the materials and the related discussions, the AM Conflicts Committee indicated that it was prepared to proceed with the negotiation of definitive Transaction Documents on substantially the same terms as each of the Conversion, the Merger, the Series B Exchange and the other transactions contemplated by the Simplification Agreement if (i) the AM Conflicts Committee retained the right to change its recommendation of the Transactions if it determined in good faith that the Transactions were no longer in the best interests of the Disinterested AM Unitholders and (ii) Antero Midstream would not be required to pay a termination fee in the event of such a change in recommendation. The AM Conflicts Committee then asked Gibson Dunn to prepare a response letter to the AMGP Conflicts Committee outlining the terms discussed. Gibson Dunn distributed the response letter to the AMGP Conflicts Committee on September 30, 2018.

        On September 30, 2018 and October 1, 2018, the AR Special Committee held meetings with Sidley, Potter Anderson and Baird to discuss the AMGP September 22 Proposal, as well as revised drafts of the Simplification Agreement and other Transaction Documents.

        On October 1, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors to discuss the letter received from the AM Conflicts Committee on September 30, 2018. The AMGP Conflicts Committee agreed that any right to change its recommendation should be tied to a concrete standard that is based on AM Conflicts Committee's obligations to the AM Public Unitholders

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and that the AMGP Conflicts Committee should have reciprocal rights. The AMGP Conflicts Committee directed its legal counsel to propose language regarding the AM Conflicts Committee's ability to change its recommendation and to negotiate a reciprocal right for the AMGP Conflicts Committee.

        On October 2, 2018, each of the committees' respective financial advisors received from Antero Management a revised financial forecast that reflected the number of AMGP Common Shares and AM Common Units then-outstanding, the latest drafts of the Simplification Agreement and other Transaction Documents and an updated New AM illustrative dividend policy that reflected ongoing negotiations among the committees.

        On October 2, 2018 and October 3, 2018, the AM Conflicts Committee held telephonic meetings with representatives of Tudor Pickering and Gibson Dunn to review Tudor Pickering's analysis of the Merger Consideration, focusing on the consideration to be received by the Disinterested AM Unitholders, and the status of the Simplification Agreement. Tudor Pickering also provided an analysis of the exchange ratio and special distribution to be received under the proposed terms of the Transactions, along with the expected distribution coverage at New AM. In addition, the group discussed the proposed illustrative dividend targets for New AM. Representatives of Gibson Dunn walked the AM Conflicts Committee members through the key provisions of the draft Simplification Agreement and the other documents proposed to be entered into with respect to the Transactions and possible revisions to be proposed, which included, among other things, provisions for direct indemnification of the members of the AM Conflicts Committee by New AM, the ability for the AM Conflicts Committee to change its recommendation with respect to the Transactions without subjecting Antero Midstream to payment of a termination fee, and representations with respect to SEC filings. Following the discussion, the AM Conflicts Committee instructed Gibson Dunn to prepare a revised draft of the Simplification Agreement incorporating the suggested revisions. Gibson Dunn distributed a revised draft of the Simplification Agreement reflecting the comments discussed as well as comments from the AR Special Committee to V&E on October 3, 2018.

        On October 3, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. There was discussion of Antero Midstream's outstanding bonds and certain credit-positive factors and potential credit-negative considerations of New AM. The AMGP Conflicts Committee then discussed an illustrative dividend policy for New AM.

        On October 6, 2018, V&E distributed revised drafts of the Transaction Documents to each of the Outside Legal Advisors, reflecting input received over the course of the week from each of the AR Special Committee, the AM Conflicts Committee, the AMGP Conflicts Committee, the Sponsor Holders and Messrs. Rady and Warren, as applicable, including the advice and guidance of their respective Outside Legal Advisors. This input reflected, among other things, ongoing discussions regarding the proposed treatment of the cash consideration to be paid in the Merger and the standards by which the AMGP Conflicts Committee and Antero Midstream Conflicts Committee would be permitted to change their recommendations with respect to the Transactions.

        On October 6, 2018, the AM Conflicts Committee participated in a teleconference with representatives of Gibson Dunn and Tudor Pickering to discuss Tudor Pickering's updated financial analysis and presentation. The Conflicts Committee and Gibson Dunn also discussed the current status of the Simplification Agreement draft, including that the changes proposed by the AM Conflicts Committee to the Simplification Agreement had been accepted. In addition, the group discussed whether there were any outstanding items relating to the Transactions the AM Conflicts Committee desired to negotiate further, including the illustrative dividend targets of New AM and the AM Conflicts Committee's desire to increase those targets by 3%. Tudor Pickering discussed in detail the updates to its materials to reflect the Merger Consideration, the inclusion of information regarding recent peer simplification transactions and an updated peer group trading analysis. During the

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presentation, the AM Conflicts Committee asked, and representatives of Tudor Pickering answered, questions with respect to Tudor Pickering's financial analysis. The AM Conflicts Committee undertook to reach out to representatives of the AR Special Committee to discuss the proposed increase to the illustrative dividend targets.

        The AR Special Committee met again on October 6, 2018 in order for Baird to provide an updated Series B Unit valuation comparison using the latest metrics and proposed economic terms. On October 7, 2018, Baird prepared a draft summary of the final proposed economic terms and its draft fairness presentation. Baird presented to the AR Special Committee the proposed transaction summary and provided analysis on the transaction, valuation, Merger Consideration and supplemental analysis requested by the AR Special Committee.

        On October 6, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. There was further discussion of the Merger Consideration to be paid in the Simplification and the illustrative dividend policy as included in the updated forecast received from Antero Management on October 2, 2018.

        Later on October 6, 2018, the AMGP Conflicts Committee, the AM Conflicts Committee and the AR Special Committee received from Antero Management a revised pro forma financial forecast featuring the illustrative New AM dividend policy that had been further revised based on negotiations among the committees. There was discussion of the illustrative dividend policy and it was acknowledged that any future dividend policy and any future declaration of dividends would be determined by the New AM Board.

        In the early morning on each of October 7 and October 8, 2018, V&E distributed substantially final drafts of the Transaction Documents to each of the Outside Legal Advisors, reflecting input received over the course of those days from each of the AR Special Committee, the AM Conflicts Committee, the AMGP Conflicts Committee, the Sponsor Holders and Messrs. Rady and Warren, as applicable, including the advice and guidance of their respective Outside Legal Advisors. This input reflected, among other things, ongoing discussions with Kirkland & Ellis, Thompson Knight and Sidley with respect to the AMGP Voting Agreement, the registration rights agreement and the Stockholders' Agreement.

        On October 8, 2018, the AR Special Committee met, with representatives of Sidley and Baird participating, to discuss the Transactions and the substantially final versions of the definitive Transaction Documents. Representatives of Sidley updated the AR Special Committee on recent revisions to the definitive Transaction Documents, and the AR Special Committee discussed those documents. At the meeting, each member of the AR Special Committee confirmed the information previously provided to Sidley with respect to his or her relationships with Antero Resources, Antero Midstream, AMGP and their respective affiliates. Sidley also reviewed the independence determinations of Baird conducted to date, the nature of its relationship to and prior engagements by Antero Resources, Antero Midstream, AMGP and their respective affiliates. Baird presented to the AR Special Committee an updated presentation of its fairness materials to reflect recent changes in the terms of the Transactions. Baird then delivered orally its opinion that, as of October 8, 2018, subsequently confirmed by delivery of a written opinion dated October 8, 2018, and based upon and subject to the various assumptions, qualifications and limitations set forth in Baird's opinion, the AR Mixed Consideration to be received by Antero Resources in the Merger was fair, from a financial point of view, to Antero Resources and the unaffiliated stockholders of Antero Resources. After discussion, the AR Special Committee unanimously determined that the Transactions were fair to, and in the best interests of Antero Resources and its unaffiliated stockholders. The AR Special Committee unanimously approved recommending to the AR Board that the AR Board approve the definitive Transaction Documents to be signed by Antero Resources in the Transactions.

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        On the afternoon of October 8, 2018, the AM Conflicts Committee held a telephonic meeting with representatives of Gibson Dunn and Tudor Pickering. During this meeting, Gibson Dunn discussed updates to the Simplification Agreement since the prior meeting of the AM Conflicts Committee. Gibson Dunn discussed the duties of the AM Conflicts Committee with respect to the Transactions and reviewed the "Special Approval" standard under the Antero Midstream Partnership Agreement. Gibson Dunn also reviewed the independence determinations of Tudor Pickering conducted to date, the nature of its relationship to and prior engagements by Antero Resources, Antero Midstream, AMGP and their respective affiliates and the amount and nature of the fees it received from those parties. Prior to the meeting, each member of the AM Conflicts Committee updated and confirmed the information previously provided to Gibson Dunn with respect to his relationships with Antero Midstream and its affiliates.

        Following this discussion, representatives of Tudor Pickering reviewed their financial analysis of the Merger Consideration to be received by the Disinterested AM Unitholders with the AM Conflicts Committee. Upon the request of the AM Conflicts Committee, Tudor Pickering then rendered its oral opinion, which was subsequently confirmed by delivery of a written opinion, that, as of October 8, 2018 and based upon and subject to the assumptions, qualifications, limitations and other matters considered relevant by Tudor Pickering in connection the preparation of its opinion as set forth in its opinion, the Merger Consideration to be received by the Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement was fair, from a financial point of view, to the Disinterested AM Unitholders.

        Following that presentation, the AM Conflicts Committee discussed and then, acting in good faith, unanimously (i) determined that the Transactions are in the best interest of Antero Midstream and the Disinterested AM Unitholders, (ii) approved the Simplification Agreement and declared advisable the consummation of the Transactions, such approval constituting "Special Approval" as defined in the Antero Midstream Partnership Agreement, (iii) approved, and recommended to the Antero Midstream Board the approval of, the Simplification Agreement and the Transactions and (iv) recommended that the Antero Midstream Board submit the AM Merger Proposal to a vote of the AM Unitholders and recommended approval of the AM Merger Proposal by the AM Unitholders. See "Special Factors—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions."

        Later on October 8, 2018, the AMGP Conflicts Committee held a telephonic meeting with all of its advisors. There was discussion of the negotiated terms of the Transactions and the history of negotiations between the AMGP Conflicts Committee, the AM Conflicts Committee, the AR Special Committee and the other parties. Also at this meeting, Goldman Sachs delivered its oral opinion to the AMGP Conflicts Committee, which was subsequently confirmed by delivery of a written opinion of Goldman Sachs, dated October 9, 2018, to the effect that, based upon and subject to the factors and assumptions set forth therein, as of the date of such opinion and after giving effect to the issuance of shares of New AM Common Stock pursuant to the Series B Exchange, the Aggregate Consideration (as defined in that opinion) to be paid by AMGP for the outstanding AM Common Units pursuant to the Simplification Agreement was fair from a financial point of view to AMGP. The AMGP Conflicts Committee's legal advisors provided an update on the legal aspects of the Transactions. There was discussion of resolutions of the AMGP Conflicts Committee, the AMGP Conflicts Committee's report to the AMGP Board, and the AMGP Conflicts Committee's recommendation to the AMGP Shareholders to vote in favor of the Transactions. The AMGP Conflicts Committee then unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, (iii) recommended to the AMGP Board that the AMGP Board approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration and

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submit the AMGP Proposals to a vote of the AMGP Shareholders and (iv) recommended to the Disinterested AMGP Shareholders that the Disinterested AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, in each case on the terms set forth in the relevant Transaction Documents. Following the meeting, the AMGP Conflicts Committee joined the meeting of the AMGP Board to deliver its report and recommendations. The AMGP Conflicts Committee's approval constitutes "Special Approval" as that term is defined by the AMGP Partnership Agreement.

        Later on October 8, 2018, following the AMGP Conflicts Committee meeting, the AMGP Board held a meeting at which representatives from Antero Management and V&E participated, and at which representatives of Hunton Andrews Kurth, Richards Layton and Goldman Sachs were also present for portions. Prior to the meeting, substantially final versions of the Simplification Agreement and other Transaction Documents were distributed to the AMGP Board, and during the meeting representatives of V&E summarized the Transactions and the key provisions of the Simplification Agreement and the other Transaction Documents. The AMGP Conflicts Committee then reviewed with the AMGP Board its process in evaluating, negotiating and recommending the Transactions to the AMGP Board, and its rationale therefor (which rationale included the reasons set forth under "—Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transaction"), and gave the AMGP Board members an opportunity to ask questions of the AMGP Conflicts Committee and its advisors at Goldman Sachs, Hunton Andrews Kurth and Richards Layton. Mr. Klimley advised the AMGP Board that the AMGP Conflicts Committee (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents, (iii) recommended to the AMGP Board that the AMGP Board approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents, and submit the AMGP Proposals to a vote of the AMGP Shareholders and (iv) recommended to the Disinterested AMGP Shareholders that the Disinterested AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents. Following this recommendation, representatives of V&E reviewed with the members of the AMGP Board their obligations under the AMGP Partnership Agreement as well as the provisions of the AMGP Partnership Agreement that provide that AMGP GP will be deemed to have acted in "good faith" and in compliance with the AMGP Partnership Agreement so long as, among other things, either the AMGP Conflicts Committee has granted "Special Approval" of the proposed transactions or the proposed transactions were approved by Disinterested AMGP Shareholders, as required by the terms of the Simplification Agreement. After discussion of the various considerations relating to the proposed transaction, the AMGP Board unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents and (iii) recommended to the AMGP Shareholders that the AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other Transaction Documents.

        Later on October 8, 2018, following the AR Special Committee meeting as well as the meetings of the AM Conflicts Committee, the AMGP Conflicts Committee and the AMGP Board, the AR Board

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held a meeting at which representatives from Antero Management and V&E participated, and at which representatives of Sidley, J.P. Morgan and Baird were also present for portions. Prior to the meeting, substantially final versions of the Simplification Agreement and other Transaction Documents were distributed to the AR Board, and during the meeting representatives of V&E summarized the Transactions and the key provisions of the Simplification Agreement and the other Transaction Documents. The AR Special Committee then reviewed with the AR Board its process in evaluating, negotiating and recommending the Transactions to the AR Board, and its rationale therefor (which rationale included the reasons set forth under "—Position of Antero Resources as to the Fairness of the Transactions"), and gave the AR Board members an opportunity to ask questions of the AR Special Committee and its advisors at Baird and Sidley. On behalf of the AR Special Committee, a representative of Sidley advised the AR Board that the AR Special Committee unanimously determined that the Simplification Agreement and the Transactions are fair to, and in the best interest of, Antero Resources and Antero Resources' unaffiliated stockholders. Based upon that determination, the AR Special Committee recommended to the AR Board that the AR Board unanimously approve the documents to which Antero Resources is a party relating to the Simplification Agreement, including the AR Voting Agreement, the Stockholders' Agreement and the registration rights agreement, and to determine that the Transactions are fair to, and in the best interests of, Antero Resources and Antero Resources' unaffiliated stockholders. Following this recommendation, representatives of V&E reviewed with the members of the AR Board their fiduciary duties under Delaware law. After discussion of the various considerations relating to the Transactions, by majority vote the AR Board determined that the Transactions were fair to, and in the best interests of Antero Resources and its unaffiliated stockholders.

        Later on October 8, 2018, following the AM Conflicts Committee meeting as well as the meetings of the AR Special Committee, the AMGP Conflicts Committee, the AMGP Board and the AR Board, the AM Board held a meeting at which representatives from Antero Management and V&E participated, and at which representatives from Gibson Dunn and Tudor Pickering were also present for portions. Prior to the meeting, substantially final versions of the Simplification Agreement and other Transaction Documents were distributed to the AM Board, and during the meeting representatives of V&E summarized the Transactions and the key provisions of the Simplification Agreement and the other Transaction Documents. The AM Conflicts Committee then reviewed with the AM Board its process in evaluating, negotiating and recommending the Transactions to the AM Board, and its rationale therefor (which rationale included the reasons set forth under "—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transaction"), and gave the AM Board members an opportunity to ask questions of the AM Conflicts Committee and its advisors at Gibson Dunn and Tudor Pickering. Mr. Peters advised the AM Board that the AM Conflicts Committee (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents, are in the best interests of AM and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents, (iii) recommended to the AM Board that the AM Board approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents, and submit the AM Merger Proposal to a vote of the AM Unitholders and (iv) recommended to the Disinterested AM Unitholders that the Disinterested AM Unitholders approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents.

        Following the recommendation, a representative of Gibson Dunn summarized for the AM Board certain results of the their due diligence review with respect to the independence of the AM Conflicts Committee. Within that discussion, Gibson Dunn noted that Mr. Mollenkopf had contacted Gibson Dunn regarding certain facts in connection with his service in an advisory role as a member of the University of Colorado Boulder's Engineering Advisory Council and as an adjunct instructor at

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University of Colorado Boulder, for which he receives insignificant compensation. Specifically, Gibson Dunn advised that Mr. Rady has made substantial charitable donations to Western Colorado University and the University of Colorado Boulder and Mr. Rady was expected to join the University of Colorado Engineering Advisory Council in October 2018. Based on the fact that Mr. Mollenkopf played no role in the solicitation of any charitable donation from Mr. Rady and received no personal benefit from any such donation, that the charitable donations were not given as a result of or in connection with the Potential Simplification, and because Mr. Mollenkopf played no role in recruiting Mr. Rady to serve on the University of Colorado Engineering Advisory Council, the AM Board determined that this relationship was not material and that Mr. Mollenkopf was still qualified to serve as a member the AM Conflicts Committee.

        Following this discussion, representatives of V&E reviewed with the members of the AM Board their obligations under the AM Partnership Agreement as well as the provisions of the AM Partnership Agreement that provide that AMP GP will be deemed to have acted in "good faith" and in compliance with the AM Partnership Agreement so long as, among other things, either the AM Conflicts Committee has granted "Special Approval" of the proposed transactions or the proposed transactions were approved by Disinterested AM Unitholders, as required by the terms of the Simplification Agreement. After discussion of the various considerations relating to the Transactions, the AM Board unanimously (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents, are in the best interests of AM and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents and (iii) recommended to the AM Unitholders that the AM Unitholders approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other Transaction Documents.

        Early on the morning of October 9, 2018, the parties finalized and executed the Simplification Agreement and certain of the other Transaction Documents and each of Antero Resources and AMGP and Antero Midstream issued press releases announcing the Transactions.

Recommendation of the AMGP Conflicts Committee and the AMGP Board and Their Reasons for Recommending Approval of the Transactions

        The AMGP Conflicts Committee consists of two directors who satisfy the requirements to serve on a conflicts committee in the AMGP Partnership Agreement: Brooks J. Klimley (Chairman) and Rose M. Robeson. The AMGP Board authorized the AMGP Conflicts Committee to (i) to the extent the AMGP Conflicts Committee deems advisable, consider, review, analyze and evaluate one or more transactions involving Antero Midstream and/or AMGP, (ii) make such investigation of potential alternatives to such transactions, including maintaining the status quo as the AMGP Conflicts Committee deems necessary or appropriate, (iii) authorize, empower or direct the officers and employees of AMGP GP and its subsidiaries to provide the AMGP Conflicts Committee with information and assistance as may be requested by the AMGP Conflicts Committee, (iv) review, evaluate, solicit, structure, and, if deemed sufficiently favorable to the interests of AMGP, negotiate, or delegate the ability to negotiate to any persons, the terms and provisions, and determine the advisability, of one or more such transactions, (v) determine whether or not to approve one or more such transactions by "Special Approval" and (vi) make a recommendation to the full AMGP Board to approve or disapprove any such transaction.

        The AMGP Conflicts Committee retained each of Hunton Andrews Kurth LLP and Richard, Layton & Finger, P.A. as its legal counsel and Goldman Sachs as its financial advisor. The AMGP Conflicts Committee oversaw the performance of financial and legal due diligence by its advisors, conducted an extensive review and evaluation of the potential Transactions, including with respect to withholding "Special Approval" and maintaining the status quo, and conducted extensive negotiations

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with the AM Conflicts Committee and the AR Special Committee and their respective representatives with respect to the Simplification Agreement and other related agreements. The AMGP Conflicts Committee engaged in extensive review and negotiations for more than six months, considering a number of alternative structures for a Potential Simplification, including (1) an acquisition of Antero Midstream by AMGP in a 100% stock transaction, and (2) a recapitalization involving elimination of IDRs in exchange for AM Common Units. The alternative of maintaining the status quo was considered throughout the negotiations until October 8, 2018, when the Transactions were approved. In determining to approve the Transactions rather than the status quo or any of the alternative transaction structures considered, the AMGP Conflicts Committee considered the factors described below.

        On October 8, 2018, the AMGP Conflicts Committee unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, (iii) recommended to the AMGP Board that the AMGP Board approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, and submit the AMGP Proposals to a vote of the AMGP Shareholders and (iv) recommended to the Disinterested AMGP Shareholders that the Disinterested AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents. The AMGP Conflicts Committee's approval constitutes "Special Approval," as such term is defined in the AMGP Partnership Agreement.

        Later on October 8, 2018, upon receiving the recommendation of the AMGP Conflicts Committee and a report of, among other things, its reasons for recommending approval of the Transactions, the AMGP Board unanimously (i) determined in good faith that the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AMGP and the Disinterested AMGP Shareholders, (ii) approved the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents and (iii) recommended to the AMGP Shareholders that the AMGP Shareholders approve the Transactions, including the Merger and the issuance or payment of the Merger Consideration, on the terms set forth in the Simplification Agreement and the other transaction documents.

        The AMGP Conflicts Committee consulted with its financial and legal advisors and considered many factors in making its determination and approvals, and the related recommendation to the Disinterested AMGP Shareholders. The AMGP Conflicts Committee considered the following factors to be generally positive or favorable in making its determination and approvals, and the related recommendation to the AMGP Board and Disinterested AMGP Shareholders and the AMGP Board also considered such factors as part of its consideration of the recommendation of the AMGP Conflicts Committee:

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The AMGP Conflicts Committee's belief that the Transactions present the best opportunity to maximize value for the Disinterested AMGP Shareholders, which belief is based on an evaluation of alternative transaction structures (including maintaining the status quo).

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The AMGP Conflicts Committee's belief, based on extensive negotiations and analysis, that the consideration to be paid to the holders of AM Common Units in the Transactions represent the least amount of consideration that the holders of AM Common Units would be willing to accept in order to agree to the Transactions.

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•

The Transactions are expected to be immediately accretive to the Disinterested AMGP Shareholders with regard to cash flow per share and dividends per share as compared to the status quo.

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The AMGP Conflicts Committee's belief that New AM's potential investor base will expand over time given perceived institutional preference for traditional C-Corp structures and governance.

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The AMGP Conflicts Committee's belief that New AM's structure will significantly increase the potential, over time, for New AM to be eligible for inclusion in major indices, which would further expand the universe of investors and enhance financial valuation and flexibility relative to AMGP today.

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New AM's larger public float relative to the float of the AMGP Common Shares should increase its ability to raise capital in the public equity markets and provide greater trading liquidity to shareholders as compared to the status quo.

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The elimination of the burden of Antero Midstream's incentive distribution rights and the elimination of the Series B Units will reduce New AM's cost of equity capital relative to the current combined status quo Antero Midstream and AMGP business.

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As a result of the Transactions, based on management's projections, New AM is not expected to pay material U.S. federal and state income taxes through 2024.

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The financial analyses prepared by Goldman Sachs, as financial advisor to the AMGP Conflicts Committee, and the oral opinion of Goldman Sachs delivered to the AMGP Conflicts Committee on October 8, 2018, which was subsequently confirmed by delivery of a written opinion of Goldman Sachs, dated October 9, 2018, to the effect that, as of such date and based upon and subject to the factors and assumptions set forth therein, after giving effect to the issuance of shares of New AM Common Stock pursuant to the Series B Exchange (as defined in such opinion), the Aggregate Consideration (as defined in such opinion) to be paid for the outstanding AM Common Units pursuant to the Simplification Agreement is fair from a financial point of view to AMGP.

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New AM will be governed with a traditional C-Corp structure that provides valuable governance protections and shareholder rights for the Disinterested AMGP Shareholders that they do not have today.

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The Disinterested AMGP Shareholders, as New AM Stockholders, will have the right to vote in the election of the directors of New AM and a majority of the directors of New AM will not be affiliated with Antero Resources, the Sponsor Holders or the Management Holders.

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The Transactions will eliminate certain control rights that the equity owners of AMGP GP currently have over the combined business of AMGP and Antero Midstream.

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The Transactions are subject to the approval by (i) the holders of a majority of the AMGP Common Shares and (ii) a majority of the Disinterested AMGP Shareholders.

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The Transactions will meaningfully reduce the complexities of the status quo organizational structure of AMGP and its subsidiaries, thereby streamlining corporate governance matters, reducing potential for conflicts of interests between AMGP, Antero Midstream and Antero Resources, and more closely aligning their interests over the long term.

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The AMGP Conflicts Committee's belief that the combination of structural simplification and improved cost of equity capital created by the Transactions will improve New AM's competitiveness in the midstream oil and gas industry, increasing the potential for future growth.

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•

The consideration to be issued or paid in the Transactions is fixed and therefore the number of shares to be issued by New AM will not increase in the event that the market price of the AMGP Common Shares decreases prior to the closing of the Transactions.

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The inclusion of cash as part of the consideration paid to holders of AM Common Units reduces the dilution to the Disinterested AMGP Shareholders relative to a potential alternative structure that contemplated the payment of only equity by New AM.

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The elimination of the Series B Units will eliminate the overhang of dilutive future conversions of Series B Units to New AM Common Stock.

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The elimination of the Series B Units will eliminate the stream of distributions that otherwise would have been payable under the terms of the IDR Holdings LLC Agreement.

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The AMGP Conflicts Committee's belief, based on extensive negotiations and analysis, that the consideration to be paid to the holders of Series B Units in the Transactions represents the least amount of consideration that the holders of Series B Units would be willing to accept in order to agree to the Transactions.

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The agreement by the Series B Holders to continue vesting restrictions and forgo cash distributions or dividends paid in 2019 on any Series B Units or Series B Exchange Shares, as applicable, that are scheduled to vest on December 31, 2019.

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Certain terms of the Simplification Agreement, principally:

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Provisions permitting the AMGP Conflicts Committee to change or withdraw its recommendation to the Disinterested AMGP Shareholders in favor of the Transactions if the AMGP Conflicts Committee determines in good faith, after consultation with its outside legal advisors and financial advisors, that the Transactions are no longer in the best interests of the Disinterested AMGP Shareholders.

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The Simplification Agreement does not require AMGP to pay a termination fee or expenses of Antero Midstream in the event that the AMGP Conflicts Committee changes or withdraws its recommendation to the Disinterested AMGP Shareholders in accordance with the Simplification Agreement.

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Antero Resources has entered into the AR Voting Agreement pursuant to which Antero Resources agreed to vote all of its AM Common Units in favor of the Transactions.

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The Transactions will allow AMGP and Antero Midstream to achieve synergies in the form of cost savings and other efficiencies, including a reduction in the number of public company boards and other costs associated with multiple public companies.

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A number of factors relating to the procedural safeguards involved in the negotiation of the Simplification Agreement, including those discussed below, each of which supported the AMGP Conflicts Committee's determination with respect to the fairness of the Transactions to AMGP and the Disinterested AMGP Shareholders:

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Each of the members of the AMGP Conflicts Committees satisfies the requirements to serve on a conflicts committee in the AMGP Partnership Agreement.

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The AMGP Conflicts Committee's retention of financial and legal advisors with knowledge and experience with respect to public merger and acquisition transactions, MLPs, AMGP's, Antero Midstream's and Antero Resources' industry generally, and AMGP, Antero Midstream and Antero Resources particularly, as well as substantial experience advising MLPs and other companies with respect to transactions similar to the Transactions.

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•

The terms and conditions of the Transactions were determined through arm's-length negotiations among the AMGP Conflicts Committee, the AM Conflicts Committee, the AR Special Committee and the holders of a majority of the Series B Units and their respective representatives and advisors.

        The AMGP Conflicts Committee considered the following factors to be generally negative or unfavorable in arriving at its determinations and approvals, and the related recommendation to the Disinterested AMGP Shareholders:

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The Disinterested AMGP Shareholders will be forgoing potential benefits that could be realized by maintaining the status quo and remaining shareholders of a standalone entity that owns the incentive distribution rights of Antero Midstream.

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New AM may not achieve its expected financial results.

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Following 2024, based on Antero Management's projections, New AM is expected to be a cash paying federal income taxpayer.

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The exchange ratio in connection with the Merger is fixed and therefore the implied value of the consideration payable to the holders of AM Common Units will increase in the event that the market price of the AMGP Common Shares increases prior to the closing of the Transactions.

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An increase in the leverage of New AM relative to the status quo operating business of Antero Midstream due to the payment of the cash Merger Consideration and transaction costs and expenses.

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A majority of the shares of New AM will be owned by a small minority of New AM Stockholders after giving effect to the Transactions.

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The risk that the potential benefits sought in the Transactions might not be fully realized.

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Certain terms of the Simplification Agreement, principally:

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Provisions permitting the AM Conflicts Committee to change or withdraw its recommendation to the AM Public Unitholders in favor of the Transactions if the AM Conflicts Committee determines in good faith, after consultation with its outside legal advisors and financial advisors, that the Transactions are no longer in the best interests of the Disinterested AM Unitholders.

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The Simplification Agreement does not require Antero Midstream to pay a termination fee or expenses of AMGP in the event that the AM Conflicts Committee changes or withdraws its recommendation to the Disinterested AM Unitholders in favor of the Transactions in accordance with the Simplification Agreement.

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The Transactions are subject to the approval by (i) the AM Unitholders and (ii) a majority of the Disinterested AM Unitholders.

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Litigation may occur in connection with the Transactions and such litigation may increase costs and result in a diversion of management time and business focus.

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The Transactions may not be completed in a timely manner, or at all, which could result in a disruption to the business of Antero Midstream and AMGP and a decline in the trading price of AMGP Common Shares.

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AMGP has incurred and will continue to incur significant transaction costs and expenses in connection with the Transactions, regardless of whether the Transactions are completed.

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Some of the executive officers of AMGP, Antero Midstream and Antero Resources own Series B Units, and some of the executive officers and directors of AMGP, Antero Midstream and Antero

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Resources have interests in the Transactions that are different from, or in addition to, the interests of the Disinterested AMGP Shareholders generally.

        In making its determination and approvals, and the related recommendation to the AMGP Shareholders, the AMGP Conflicts Committee considered the financial analyses regarding AMGP and Antero Midstream prepared by Goldman Sachs and reviewed and discussed by Goldman Sachs with the AMGP Conflicts Committee. The financial analyses presented to the AMGP Conflicts Committee by Goldman Sachs, which included present value of future share price analysis and a discounted cash flow analysis as described under "—Opinion of the AMGP Conflicts Committee's Financial Advisor," were based on the operations of Antero Midstream as a continuing business and, to that extent, the AMGP Conflicts Committee considered such analyses as going concern valuations. The AMGP Conflicts Committee considered each of these analyses in the context of the fairness opinion provided by Goldman Sachs, and the AMGP Conflicts Committee expressly adopted these analyses and the opinion of Goldman Sachs, among the other factors it considered (as described above), in reaching its conclusions regarding the fairness of the Simplification Agreement and the Transactions to the AMGP Shareholders.

        In making its determination and approvals, and the related recommendation to the AMGP Shareholders, the AMGP Board considered a number of factors, including (i) the unanimous determination and recommendation of the AMGP Conflicts Committee and (ii) the factors considered by the AMGP Conflicts Committee, including the material factors described above. In doing so, the AMGP Board expressly adopted the analysis of the AMGP Conflicts Committee, including that of Goldman Sachs, which are discussed above.

        The foregoing discussion of the information and factors considered by the AMGP Conflicts Committee and the AMGP Board is not intended to be exhaustive, but includes material factors the AMGP Conflicts Committee and the AMGP Board considered. In view of the variety of factors considered in connection with their evaluation of the Transactions and the complexity of these matters, neither the AMGP Conflicts Committee nor the AMGP Board found it useful or attempted to quantify or assign any relative or specific weights to the various factors considered in making their determinations and recommendations. In addition, each of the members of the AMGP Conflicts Committee and the AMGP Board may have given differing weights to different factors. Overall, the AMGP Conflicts Committee and the AMGP Board believed that the positive factors supporting the Transactions outweighed the negative factors they considered.

        Under the AMGP Partnership Agreement, whenever AMGP GP, acting in its capacity as the general partner of AMGP, or the AMGP Board or any committee of the AMGP Board (including the AMGP Conflicts Committee) or any affiliates of AMGP GP cause AMGP GP to make a determination or take or omit to take any action in such capacity, then, unless another lesser standard is provided for in the AMGP Partnership Agreement (which is not the case with respect to the Transactions), AMGP GP, the AMGP Board, such committee (including the AMGP Conflicts Committee) or such affiliates, will not make such determination, or take or omit to take such action, in Bad Faith (as defined in the AMGP Partnership Agreement). Under the AMGP Partnership Agreement, a determination, action or omission by AMGP GP, the AMGP Board or any committee of the AMGP Board (including the AMGP Conflicts Committee) or of any affiliates of AMGP GP will for all purposes be presumed to have been in Good Faith (as defined in the AMGP Partnership Agreement). The AMGP Conflicts Committee has not, including, without limitation, in connection with making the determination and approvals, and the related recommendation to the Disinterested AMGP Shareholders described above, assumed any obligation to AMGP or its limited partners (whether fiduciary, contractual, implied, or otherwise) other than those obligations that may exist in the AMGP Partnership Agreement. Nothing in this joint proxy statement/prospectus or the actions, determinations or recommendations of the AMGP Conflicts Committee described in this joint proxy statement/prospectus should be read to mean that the AMGP Conflicts Committee assumed any obligations to

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AMGP or its limited partners (whether fiduciary, contractual, implied, or otherwise) other than those obligations that may exist in the AMGP Partnership Agreement. You are urged to read the full text of the AMGP Partnership Agreement, which is incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 270 of this joint proxy statement/prospectus.

Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions

        The AM Conflicts Committee consists of two directors who satisfy the requirements to serve on a conflicts committee in the Antero Midstream Partnership Agreement: David A. Peters (Chairman) and John C. Mollenkopf. The AM Board authorized the AM Conflicts Committee to (i) consider, review and evaluate one or more transactions involving Antero Midstream and/or AMGP, (ii) make such investigation of potential alternatives to such transactions, including maintaining the status quo, (iii) authorize, empower or direct the officers and employees of AMP GP and its subsidiaries to provide the AM Conflicts Committee with information and assistance as may be requested by the AM Conflicts Committee, (iv) review, evaluate, and negotiate, or delegate the ability to negotiate to any persons, the terms and provisions, and determine the advisability, of one or more such transactions, (v) determine whether or not to approve one or more such transactions by "Special Approval" and (vi) make a recommendation to the full AM Board to approve or disapprove any such transaction.

        The AM Conflicts Committee retained Gibson, Dunn & Crutcher LLP as its legal counsel and Tudor Pickering as its financial advisor. The AM Conflicts Committee oversaw the performance of financial and legal due diligence by its advisors, conducted an extensive review and evaluation of the potential Transactions, including with respect to withholding "Special Approval" and maintaining the status quo, and conducted extensive negotiations with the AMGP Conflicts Committee and the AR Special Committee and their respective representatives with respect to the Simplification Agreement and other related agreements. The AM Conflicts Committee engaged in extensive review and negotiations for more than six months. Throughout the negotiations until October 8, 2018, when the Transactions were approved, the AM Conflicts Committee considered the Transactions as proposed by the AMGP Conflicts Committee (including the various consideration mixes included in these proposals), as well as maintaining the status quo. In determining to approve the Transactions rather than the status quo, the AM Conflicts Committee considered the factors described below.

        On October 8, 2018, the AM Conflicts Committee unanimously (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of Antero Midstream and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, (iii) recommended to the AM Board that the AM Board approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, and submit the AM Merger Proposal to a vote of the AM Unitholders, and (iv) recommended to the Disinterested AM Unitholders that the Disinterested AM Unitholders approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents. The AM Conflicts Committee's approval constitutes "Special Approval," as such term is defined in the Antero Midstream Partnership Agreement.

        Later on October 8, 2018, upon receiving the recommendation of the AM Conflicts Committee and a report of, among other things, its reasons for recommending approval of the Transactions, the AM Board unanimously (i) determined in good faith that the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents, are in the best interests of AM and the Disinterested AM Unitholders, (ii) approved the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction

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documents and (iii) recommended to the AM Unitholders that the AM Unitholders approve the Transactions, including the Merger, on the terms set forth in the Simplification Agreement and the other transaction documents.

        The AM Conflicts Committee considered the following factors to be generally positive or favorable in making its determination and approvals, and the related recommendation to the AM Unitholders:

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The Simplification Agreement provides for AM Public Unitholders to receive, subject to the election described below, 1.6350 shares of New AM Common Stock and $3.415 in cash for each AM Common Unit held by the AM Public Unitholders, which constitutes an improvement over AMGP's initial proposal of 1.6 shares of New AM Common Stock and no cash for each AM Common Unit.

•

Based on the closing price of AM Common Units as of October 8, 2018 (the last trading day before the day the Simplification Agreement was announced), the Merger Consideration for the AM Public Unitholders represented an implied premium of approximately 7% above the closing price of AM Common Units as of October 8, 2018 and approximately 31% above the closing price of AM Common Units as of February 23, 2018, which was the last trading day prior to the announcement of the formation of the AM Conflicts Committee.

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The cash component of the Public Mixed Consideration is expected to provide the average AM Public Unitholder adequate cash to (i) fully satisfy tax obligations resulting from the Transactions and (ii) on an after-tax basis, partially offset the proposed reduction in New AM's projected dividends.

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The Simplification Agreement provides that, subject to proration, each AM Public Unitholder may elect to receive all cash, all New AM Common Stock, or a combination of cash and New AM Common Stock, thereby providing AM Public Unitholders the choice of investing in New AM following the Transactions or receiving a higher percentage of cash for their AM Common Units to use for other purposes.

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New AM's pro forma dividend targets (before giving effect to taxes) represent an approximate 3% increase for AM Unitholders compared to existing status quo Antero Midstream distribution targets and growth rates through 2022 (assuming AM Public Unitholders elect to receive all equity consideration).

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The Transactions will be (i) immediately accretive to AM Public Unitholders before giving effect to taxes payable with respect to the Transactions and (ii) accretive to AM Public Unitholders following 2019 after giving effect to taxes payable with respect to the Transactions, in each case on a distributable cash flow basis as compared to the status quo.

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New AM's status as a corporation following the Transactions provides a number of benefits relative to Antero Midstream's status quo current structure, including (i) a lower cost of capital by eliminating the burden of Antero Midstream's incentive distribution rights, (ii) better trading liquidity, (iii) simplified tax structure by the elimination of K-1 tax reporting requirements, (iv) a broader set of potential investors as compared to master limited partnerships as certain types of institutional investors face prohibitions or limitations on investing in entities other than corporations, (v) the potential for a superior pro forma dividend yield as compared to Antero Midstream based on historical trading in corporations similar to New AM and (vi) enhanced voting and other governance rights as stockholders of a corporation as compared to unitholders of a master limited partnership controlled by a general partner.

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•

The Public Mixed Consideration is fixed and therefore the value of the New AM Common Stock to be received as part of the Merger Consideration by any AM Public Unitholder that elects to receive the Public Mixed Consideration would increase in the event the market price of New AM Common Stock or the AMGP Common Shares increased prior to the closing of the Merger.

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The AM Conflicts Committee's belief that the Merger Consideration for Disinterested AM Unitholders represents the greatest amount of consideration that AMGP would have been willing to agree to pay at the time of the AM Conflicts Committee's determination and approval.

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The valuation analyses of Antero Midstream and AMGP prepared by Tudor Pickering and reviewed and discussed with the AM Conflicts Committee, including, among other things, a discounted cash flow analysis, a precedent transactions analysis, a peer group trading analysis and a premiums paid analysis.

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The delivery of an opinion by Tudor Pickering to the AM Conflicts Committee on October 8, 2018, to the effect that, as of that date and based upon and subject to the assumptions, qualifications, limitations and other matters considered relevant by Tudor Pickering as set forth in its written opinion, the Merger Consideration to be received by the Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement was fair, from a financial point of view, to the Disinterested AM Unitholders.

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As a result of the Transactions, based on Antero Management's projections, New AM is not expected to pay material U.S. federal and state income taxes through 2024, thereby facilitating higher dividends initially and over time, which will benefit AM Public Unitholders receiving New AM Common Stock in the Merger as compared to the status quo.

•

Certain terms of the Simplification Agreement, principally:

•

the ability of the AM Conflicts Committee and the AM Board to change their recommendation of the AM Merger Proposal, without Antero Midstream being required to pay a termination fee, in the event either the AM Conflicts Committee or the AM Board makes a good faith determination that the Transactions are no longer in the best interests of the Disinterested AM Unitholders;

•

the Transactions being conditioned upon approval of the AM Merger Proposal by of a majority of the Disinterested AM Unitholders; and

•

the pre-closing operating covenants for AMGP, which provide protection to AM Unitholders by restricting AMGP's ability to take certain actions prior to the closing of the Transactions that could reduce the value of the Merger Consideration to the Disinterested AM Unitholders.

        In addition, the AM Conflicts Committee also considered a number of factors relating to the procedural safeguards involved in the negotiation of the Simplification Agreement, including those discussed below, each of which supported its determination with respect to the fairness of the Transactions to the Disinterested AM Unitholders:

•

Each of the members of the AM Conflicts Committees satisfies the requirements for serving on the AM Conflicts Committee, including the requirement that all members of the AM Conflicts Committee be independent.

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In connection with the consideration of the Transactions, the AM Conflicts Committee retained its own independent financial and legal advisors with knowledge and experience with respect to public merger and acquisition transactions, and AMGP's and Antero Midstream's industry

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specifically, as well as substantial experience advising publicly traded master limited partnerships and other companies with respect to transactions similar to the Transactions.

•

The terms and conditions of the Simplification Agreement and the Transactions were determined through arm's-length negotiations between the AMGP Conflicts Committee, the AR Special Committee, the AM Conflicts Committee, the holders of a majority of the Series B Units and their respective representatives and advisors.

•

Under the terms of the Simplification Agreement, prior to the effective time of the Merger, AMGP will not, without the consent of the AM Conflicts Committee, eliminate the AM Conflicts Committee, revoke or diminish the authority of the AM Conflicts Committee or remove or cause the removal of any member of the AM Board who is a member of the AM Conflicts Committee either as a director or as a member of such committee.

        The AM Conflicts Committee considered the following factors to be generally negative or unfavorable in making its determination and approvals, and the related recommendation to the AM Unitholders:

•

The receipt of New AM Common Stock, cash or a combination of New AM Common Stock and cash in exchange for AM Common Units pursuant to the Merger will be a taxable transaction for U.S. federal income tax purposes to U.S. holders (as defined in "Material U.S. Federal Income Tax Consequences" beginning on page 254 of this joint proxy statement/prospectus). However, the cash portion, if elected, of the Merger Consideration may be used by AM Unitholders to pay a portion of the taxes incurred.

•

The Public Mixed Consideration is fixed and therefore the value of the New AM Common Stock to be received as part of the Merger Consideration by any AM Public Unitholder that elects to receive the Public Mixed Consideration would decrease in the event the market price of the AMGP Common Shares decreased prior to the closing of the Merger.

•

AM Unitholders are not entitled to appraisal rights under the Simplification Agreement or Delaware law.

•

The AM Conflicts Committee did not conduct an auction process or other solicitation of interest from third parties for the acquisition of Antero Midstream or of the AM Common Units held by the public.

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There is risk that the potential benefits sought in the Transactions might not be fully realized.

•

There is risk that the Transactions might not be completed in a timely manner, or that the Transactions might not be consummated at all as a result of a failure to satisfy the conditions contained in the Simplification Agreement, and a failure to complete the Transactions could negatively affect the trading price of AM Common Units.

•

AM Unitholders will be forgoing the potential benefits that would be realized by maintaining the status quo and remaining unitholders of Antero Midstream on a standalone basis.

•

Litigation may occur in connection with the Transactions and such litigation may increase costs and result in a diversion of management focus.

•

Certain members of Antero Midstream management and the AM Board may have interests that are different from those of the Disinterested AM Unitholders.

        In making its determination and approvals, and the related recommendation to the AM Unitholders, the AM Conflicts Committee considered the financial analyses regarding Antero Midstream prepared by Tudor Pickering and reviewed and discussed by Tudor Pickering with the AM Conflicts Committee. The financial analyses presented to the AM Conflicts Committee by Tudor

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Pickering, which included, among other things, a discounted distribution analysis, a contribution analysis, an accretion/dilution analysis, a precedent transactions analysis, a peer group trading analysis and a premiums paid analysis as described under "—Opinion of the AM Conflicts Committee's Financial Advisor" were based on the operations of Antero Midstream as a continuing business and, to that extent, the AM Conflicts Committee considered such analyses as going concern valuations. The AM Conflicts Committee considered each of these analyses in the context of the fairness opinion provided by Tudor Pickering, and the AM Conflicts Committee expressly adopted these analyses and the opinion of Tudor Pickering, among the other factors it considered (as described above), in reaching its conclusions regarding the fairness of the Simplification Agreement and the Transactions to the AM Unitholders.

        In making its determination and approvals, and the related recommendation to the AM Unitholders, the AM Board considered a number of factors, including (i) the unanimous determination and recommendation of the AM Conflicts Committee and (ii) the factors considered by the AM Conflicts Committee, including the material factors described above. In doing so, the AM Board expressly adopted the analysis of the AM Conflicts Committee, including that of Tudor Pickering, which are discussed above.

        The foregoing discussion of the information and factors considered by the AM Conflicts Committee and the AM Board is not intended to be exhaustive, but includes material factors the committee and board considered. In view of the variety of factors considered in connection with their evaluation of the Transactions and the complexity of these matters, neither the AM Conflicts Committee nor the AM Board found it useful or attempted to quantify or assign any relative or specific weights to the various factors considered in making their determinations and recommendations. In addition, each of the members of the AM Conflicts Committee and the AM Board may have given differing weights to different factors. Overall, the AM Conflicts Committee and the AM Board believed that the positive factors supporting the Transactions outweighed the negative factors they considered.

        AMP GP, the AM Conflicts Committee and the AM Board have not, including, without limitation, in making the determinations set forth above, assumed any obligations to the AM Unitholders (whether fiduciary, contractual, implied, or otherwise) other than those obligations that may exist in the Antero Midstream Partnership Agreement. Under the Antero Midstream Partnership Agreement, whenever AMP GP makes a determination or takes or omits to take any other action (including action taken by the AM Board or any committee thereof (including the AM Conflicts Committee)), in its capacity as the general partner of Antero Midstream, AMP GP, the AM Board or the applicable committee thereof (including the AM Conflicts Committee) must not make such determination or take or omit to take such other action in "Bad Faith", and such determination, action or omission is not subject to any other or different standard under applicable law. Under the Antero Midstream Partnership Agreement, "Bad Faith" means, with respect to any determination, action or omission of any person, board or committee, that such person, board or committee reached such determination, or engaged in or failed to engage in such act or omission, with the belief that such determination, action or omission was adverse to the interest of Antero Midstream. Under the Antero Midstream Partnership Agreement, any determination, action or omission by AMP GP (including, as applicable, the AM Board or the applicable committee thereof (including the AM Conflicts Committee)) will for all purposes be presumed to have been in "Good Faith" (meaning that such determination, action or omission was not taken in "Bad Faith"). Nothing in this joint proxy statement/prospectus or the actions or determinations of AMP GP, the AM Conflicts Committee, or the AM Board described in this joint proxy statement/prospectus should be read to mean that AMP GP, the AM Conflicts Committee or the AM Board assumed any obligations to Antero Midstream or its limited partners (whether fiduciary, contractual, implied, or otherwise) other than those obligations that may exist in the Antero Midstream Partnership Agreement. You are urged to read the full text of the Antero Midstream Partnership Agreement, which

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is incorporated by reference into this joint proxy statement/prospectus. See "Where You Can Find More Information" beginning on page 270 of this joint proxy statement/prospectus.

Position of Antero Resources as to the Fairness of the Transactions

        Under the rules governing "going private" transactions, Antero Resources is deemed to be engaged in a "going private" transaction and is required to express its beliefs as to the fairness of the Transactions to the Disinterested AM Unitholders pursuant to Rule 13e-3 under the Exchange Act. Antero Resources and the AR Special Committee are making the statements included in this section solely for the purposes of complying with the requirements of Rule 13e-3 and related rules under the Exchange Act. The AR Board delegated to the AR Special Committee the full power, authority and responsibility of the AR Board with respect to the review, evaluation and approval or disapproval of, the terms relating to a range of strategies and transactions, to determine, in the AR Special Committee's sole discretion, whether the transaction is fair to, and in the best interests of, Antero Resources and Antero Resources' unaffiliated stockholders, and to make a recommendation to the AR Board to approve or disapprove a transaction. The views of the AR Special Committee as to the fairness of the Transactions should not be construed as a recommendation to any Disinterested AM Unitholder as to how that unitholder should vote on the AM Merger Proposal or any Disinterested AMGP Shareholder as to how that shareholder should vote on the AMGP Proposals.

        On October 8, 2018, the AR Special Committee determined that the Simplification Agreement and Transactions are fair to, and in the best interest of, Antero Resources and Antero Resources' unaffiliated stockholders. Based upon that determination, the AR Special Committee recommended to the AR Board that the AR Board approve the documents to which Antero Resources is a party relating to the Simplification Agreement, including the AR Voting Agreement, the Stockholders' Agreement and the registration rights agreement, and to determine that the Transactions are fair to, and in the best interests of, Antero Resources and Antero Resources' unaffiliated stockholders. The AR Board, including a majority of the directors of the AR Board who are not employees of Antero Resources, approved the Transactions and determined that the Transactions are fair to, and in the best interests of, Antero Resources and Antero Resources' unaffiliated stockholders.

        The AR Special Committee consulted with its financial and legal advisors and considered many factors in making its determination and approvals, and the related recommendations to the AR Board. The Simplification Agreement provides a requirement that a majority of the Disinterested AM Unitholders vote in favor of the Transactions. While the AR Special Committee was neither authorized nor asked to deliver a recommendation to the Disinterested AM Unitholders, as an approximate 53% holder of AM Common Units, there were many factors that it considered in making its determination as to the fairness of the Transactions that would likely be relevant to the Disinterested AM Unitholders as well. The AR Special Committee considered, among other factors, the following factors to be generally positive or favorable in making its determination:

•

The Merger Consideration to be paid to Antero Resources, as a holder of AM Common Units, represented:

•

a 3% premium to Antero Midstream's closing price on October 8, 2018 (the last trading day before the announcement of the Simplification Agreement); and

•

a 27% premium to Antero Midstream's closing price on February 23, 2018 (the last trading day before the announcement of the formation of the AM Conflicts Committee).

•

The Merger Consideration to be paid to the Disinterested AM Unitholders is greater than the Merger Consideration to be paid to Antero Resources, resulting in greater premiums to Disinterested AM Unitholders than to Antero Resources.

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•

The strengths of New AM and benefits to be received by the AM Unitholders, including, among others:

•

The Transactions eliminate the burden on Antero Midstream's cost of capital resulting from the level of incentive distributions payable to the holder of its incentive distribution rights, which could from time to time, if not eliminated, make it more challenging for Antero Midstream to pursue accretive acquisitions and relatively more expensive to fund its capital expenditure program;

•

The AR Special Committee's expectation that the Transactions will strengthen and enhance the pro forma balance sheet of New AM by utilizing higher retained cash flow to further deliver and to fund a portion of Antero Midstream's robust growth capital expenditure program;

•

The AR Special Committee's expectation that New AM's increased distribution coverage will provide distribution stability and long-term growth prospects, enhancing funding optionality and reducing reliance on capital markets;

•

The AR Special Committee's expectation that shares of New AM Common Stock after the Transactions will trade better on a number of metrics relative to how the AM Common Units have traded on a historic basis; and

•

The AR Special Committee's expectation that the Transactions will be distributable cash flow accretive to current AM Unitholders.

•

That New AM's dividend targets would maintain, after giving effect to Antero Resources' exchange ratio, existing distribution targets through 2022 for any holder of AM Common Units that receives only shares of New AM Common Stock as Merger Consideration.

•

In connection with the Transactions, the vesting provisions of the Series B Units to be exchanged for shares of New AM Common Stock will apply to those shares in accordance with the existing vesting terms, and holders of shares of Series B Units or Series B Exchange Shares that are scheduled to vest on December 31, 2019 will not be entitled to any distributions or dividends with respect to those unvested units or shares that are paid by IDR Holdings or New AM, as applicable, during the twelve months ending December 31, 2019.

•

The financial presentation and opinion of Baird, dated October 8, 2018, stating that as of such date, and based upon and subject to the various assumptions, qualifications and limitations set forth in Baird's opinion, the AR Mixed Consideration to be received by Antero Resources in the Merger was fair, from a financial point of view, to Antero Resources and the unaffiliated stockholders of Antero Resources, as described under "Special Factors—Opinion of the AR Special Committee Financial Advisor."

        In addition, the AR Special Committee also considered a number of factors relating to the procedural safeguards involved in the negotiation of the Simplification Agreement, including those discussed below, each of which supported its determination with respect to the fairness of the Transactions to Antero Resources and its unaffiliated stockholders:

•

The AR Special Committee consisted solely of directors who are independent and not affiliated with Antero Midstream, AMGP or any of AMGP's or Antero Midstream's affiliates (except in their capacities as directors of AR).

•

The AR Special Committee retained and was advised by experienced and qualified advisors, consisting of Sidley Austin LLP and Potter Anderson & Corroon LLP, as legal counsel, and Baird, as financial advisor.

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•

The terms and conditions of the Simplification Agreement and the Transactions were determined through arm's-length negotiations between the AMGP Conflicts Committee, the AM Conflicts Committee, the AR Special Committee, the holders of a majority of the Series B Units and their respective representatives and advisors.

        The AR Special Committee considered the following factors to be generally negative or unfavorable in making its determination and approvals:

•

In connection with the Transactions, Series B Holders will be paid shares of New AM Common Stock, which will dilute Antero Resources' and AM Public Unitholders' equity ownership of New AM.

•

The Transactions are conditioned upon Disinterested AMGP Shareholder Approval, which reduces the certainty that the Transactions will be completed.

•

Litigation may occur in connection with the Transactions and any such litigation may result in significant costs and a diversion of management focus.

•

There is risk that the Transactions might not be completed in a timely manner, or that the Transactions might not be consummated at all as a result of a failure to satisfy the conditions contained in the Simplification Agreement, and a failure to complete the Transactions could negatively affect the trading price of Antero Resources or Antero Midstream or could result in significant costs and disruption to Antero Resources' or Antero Midstream's normal business.

        The AR Special Committee considered the additional following factors in making its determination and approvals:

•

The Transactions are conditioned upon Disinterested AM Unitholder Approval.

•

Each of (i) Antero Resources, (ii) certain funds affiliated with Warburg Pincus LLC and certain funds affiliated with Yorktown Partners LLC, collectively, and (iii) Paul M. Rady and Glen C. Warren Jr., collectively (if one or both of them has not been designated by Antero Resources), will have the right to designate two directors to the New AM Board, in each case subject to meeting certain minimum ownership thresholds.

        Based on the analysis, discussion and resulting conclusions of the AR Special Committee, the AR Board believes that the Transactions are substantively and procedurally fair to the Disinterested AM Unitholders. The foregoing discussion of the information and factors considered and given weight by Antero Resources is not intended to be exhaustive, but includes the factors considered by Antero Resources that it believes to be material to the fairness determination regarding the fairness of the Transactions for the purpose of complying with the requirements of Rule 13e-3 and the related rules under the Exchange Act. Antero Resources did not find it practicable to, and did not, quantify or otherwise attach relative weights to the foregoing factors in reaching their position as to the fairness of the Transactions. Rather, Antero Resources made its fairness determination after considering all of the factors as a whole.

Position of the AMGP Parties, AM Parties, Management Holders and Sponsor Holders as to the Fairness of the Transactions

        Under the rules governing "going private" transactions, each of the AMGP Parties, AM Parties, Management Holders and Sponsor Holders are deemed to be engaged in a "going private" transaction and are required to express their beliefs as to the fairness of the Transactions to the Disinterested AM Unitholders pursuant to Rule 13e-3 under the Exchange Act. The AMGP Parties, AM Parties, Management Holders and Sponsor Holders are making the statements included in this section solely for the purposes of complying with the requirements of Rule 13e-3 and related rules under the Exchange Act.

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        The AMGP Parties, AM Parties, Management Holders and Sponsor Holders believe that the Transactions are substantively and procedurally fair to the Disinterested AM Unitholders on the basis of the factors described in the section entitled "—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions." The AM Board delegated to the AM Conflicts Committee the power and authority to review, evaluate and make a recommendation to the AM Board and the Disinterested AM Unitholders with respect to AM Merger Proposal. The AMGP Parties, AM Parties, Management Holders and Sponsor Holders believe that the interests of the Disinterested AM Unitholders were represented by the AM Conflicts Committee, which (i) negotiated the terms and conditions of the Simplification Agreement on behalf of the Disinterested AM Unitholders with the assistance of its independent legal and financial advisors, (ii) unanimously approved the Transactions, including the Merger, and (iii) made a recommendation to the AM Board that the AM Board approve the Transactions, including the Merger. Further, the Simplification Agreement requires that the AM Merger Proposal be approved by Disinterested AM Unitholder Approval. None of the Management Holders, Sponsor Holders, AMGP Parties, AM Parties or any of their directors or executive officers, other than the AM Conflicts Committee, undertook any independent evaluation of the fairness of the Transactions to the Disinterested AM Unitholders or engaged a financial advisor for such purpose.

        Although the AM Conflicts Committee and the AM Board each recommends that the AM Unitholders vote to approve the AM Merger Proposal, the views of the AMGP Parties, Management Holders and Sponsor Holders as to the fairness of the Transactions should not be construed as a recommendation to any AM Unitholder as to how that unitholder should vote on the proposal to approve the AM Merger Proposal.

        The foregoing discussion of the information and factors considered and given weight by the AMGP Parties, AM Parties, Management Holders and Sponsor Holders is not intended to be exhaustive, but includes the factors considered by them that each believes to be material to the fairness determination regarding the fairness of the Transactions to the Disinterested AM Unitholders for the purpose of complying with the requirements of Rule 13e-3 and the related rules under the Exchange Act. In reaching their position as to the fairness of the Transactions to the Disinterested AM Unitholders, the AMGP Parties, AM Parties, Management Holders and Sponsor Holders did not find it practicable to, and did not, quantify or otherwise attach relative weights to the factors described in the section entitled "—Recommendation of the AM Conflicts Committee and the AM Board and Their Reasons for Recommending Approval of the Transactions," or the procedural protection described in the preceding paragraph, which factors formed the basis of each of their fairness determinations. Rather, each made their fairness determination after considering all of the factors as a whole.

Projected Financial Information

        As part of its annual financial planning process, Antero Midstream prepares budgets for its upcoming fiscal year and a projection of operating and financial results for the five-year period beginning with that upcoming fiscal year. While Antero Midstream has historically released annual guidance from time to time, and in January 2018 published a five-year outlook, Antero Midstream does not, as a matter of course, publicly disclose its full financial projections. As the owner of AMP GP, and as a result of the substantial overlap of management and directors at both levels, AMGP has access to these projections.

        In connection with the consideration of the Potential Simplification by the AR Special Committee, the AM Conflicts Committee and the AMGP Conflicts Committee, each committee and their respective financial advisors received certain projected financial information with respect to each of Antero Midstream and AMGP on a stand-alone basis, and for New AM pro forma for the Transactions, in early April 2018 to assist in their consideration of a potential transaction. This projected financial information was updated on October 2, 2018 to reflect only the following changes:

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(i) the number of AMGP Common Shares and AM Common Units then-outstanding, (ii) the latest drafts of the Simplification Agreement and related transaction documents and (iii) updates to projected New AM pro forma dividends per share to reflect additional discussions between the parties regarding New AM's proposed dividend policy following the completion of the Transactions. This projected financial information was further updated on October 6, 2018 only to reflect further discussions between the parties regarding New AM's proposed dividend policy following the completion of the Transactions (as updated on October 6, 2018, the "Management Projections"). The Management Projections were provided to (a) Goldman Sachs and approved for its use and consideration by the AMGP Conflicts Committee in connection with, and relied upon by Goldman Sachs with respect to, its financial analyses and opinion, (b) Tudor Pickering and approved for its use and consideration by the AM Conflicts Committee in connection with, and relied upon by Tudor Pickering with respect to, its financial analyses and opinion and (c) Baird and approved for its use and consideration by the AR Special Committee in connection with, and relied upon by Baird with respect to, its financial analyses and opinion. The Management Projections were dated October 6, 2018, and were based on the information available to Antero Management as of the date of such projections and speak only as of such date, and the Management Projections have not been updated and will not be updated since such date.

        As discussed in more detail under "—Relationships of the Parties to the Transactions," there is significant overlap between the management teams of Antero Resources, Antero Midstream and AMGP, and there is complete overlap in the assets and businesses underlying each of Antero Midstream and AMGP's financial performance, given that AMGP's sole assets are direct and indirect equity interests in Antero Midstream. Accordingly, much of the prospective financial information of AMGP is derived directly from the prospective financial information of Antero Midstream. For these reasons, the Management Projections should be viewed as being jointly prepared by Antero Management.

        The Management Projections were prepared utilizing standalone projected financial information for Antero Midstream based on preliminary budgeting and forecast information. In the case of the projections related to New AM pro forma for the Transactions, models were adjusted to account for assumed equity and cash consideration, tax impacts related to the Transactions, the elimination of Series B Units and the targeted pro forma dividends of New AM during the periods covered by such projections. The reports of the independent registered public accounting firm incorporated by reference into this joint proxy statement/prospectus relate to the historical audited financial information of Antero Midstream and AMGP, respectively. Such reports do not extend to the unaudited financial projections and should not be read to do so.

        The accompanying prospective financial information was not prepared with a view toward public disclosure or with a view toward complying with the guidelines established by the American Institute of Certified Public Accountants with respect to prospective financial information, but, in the view of Antero Management, was prepared on a reasonable basis, reflected the then best currently available estimates and judgments, and presents, to the best of Antero Management's knowledge and belief, the expected course of action and the expected future financial performance of AMGP, Antero Midstream and New AM. However, this information is subject to significant economic, competitive, industry and other uncertainties, is not fact, may not be achieved in full, within projected time frames or at all and should not be relied upon as being necessarily indicative of future results, and readers of this joint proxy statement/prospectus are cautioned not to place undue reliance on the prospective financial information. Accordingly, the accompanying prospective financial information, which was utilized by Goldman Sachs, Tudor Pickering and Baird for purposes of their respective financial analyses and opinions, may not be realized.

        Neither AMGP's nor AM's independent registered public accounting firm, nor any other independent accountants, have compiled, examined or performed any procedures with respect to the

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prospective financial information contained herein, nor have they expressed any opinion or any other form of assurance on such information or its achievability, and assume no responsibility for, and disclaim any association with, the prospective financial information.

        The following table sets forth certain projected financial information for AMGP, Antero Midstream and New AM on a pro forma basis through 2022:

	2018		2019		2020		2021		2022
	($ in millions)
Antero Midstream Status Quo Adjusted EBITDA(1)	$	730	$	989	$	1,222	$	1,413	$	1,642
Antero Midstream Status Quo Distributions Per Unit	$	1.72	$	2.21	$	2.85	$	3.42	$	4.10
Antero Midstream Status Quo Distributable Cash Flow(1)	$	594	$	854	$	1,036	$	1,224	$	1,428
Antero Midstream Status Quo DCF Coverage Ratio(1)(2)		1.3x		1.3x		1.2x		1.1x		1.1x
AMGP Status Quo Distributions Per Share	$	0.54	$	0.89	$	1.34	$	1.74	$	2.22
New AM Pro Forma Adjusted EBITDA(1)			$	989	$	1,222	$	1,413	$	1,642
New AM Pro Forma Dividends Per Share			$	1.24	$	1.60	$	1.93	$	2.31
New AM Pro Forma Distributable Cash Flow(1)			$	816	$	1,001	$	1,207	$	1,392
New AM Pro Forma DCF Coverage Ratio(1)(2)				1.3x		1.2x		1.2x		1.2x

(1)

Adjusted EBITDA, Distributable Cash Flow and Net Debt are non-GAAP financial measures. For a discussion of how such terms are defined and used, please see "—Non-GAAP Financial Measures" below.

(2)

DCF Coverage Ratio defined as Distributable Cash Flow over aggregate distributions.

        Other assumptions underlying the foregoing projected financial information include, among other things:

•

Operating assumptions for Antero Resources' operations, including:

•

underlying throughput volumes driven by Antero Resources net production targets that consist of (1) 2,253 million cubic feet of natural gas equivalent per day in 2017, increasing at a compound annual growth rate of 20% from through 2020, and (2) approximately 15% net production growth in each of 2021 and 2022; and

•

Antero Resources' Stand-Alone Net Debt to Stand-Alone Adjusted EBITDAX leverage targets of low 2x in 2018 and under 2x in 2019 through 2022, based on strip commodity pricing as of December 31, 2017;

•

Operating assumptions for Antero Midstream, including the following for volumes of key products handled:

•

low pressure gathering volumes driven by Antero Resources net production targets resulting in (1) 1,660 million cubic feet of natural gas per day of low pressure gathering volumes in 2017 for Antero Midstream, increasing at a compound annual growth rate of 28% through 2020, and (2) approximately 17% and 15% volume growth in 2021 and 2022, respectively; and

•

fresh water distribution volumes driven by Antero Resources development plan resulting in (1) 153,000 barrels per day of fresh water delivery volumes in 2017 for Antero Midstream, increasing at a compound annual growth rate of 13% through 2020, and (2) approximately 10% and 7% volume growth in 2021 and 2022, respectively;

•

Future prices of oil, natural gas and NGLs based on NYMEX futures pricing as of December 31, 2017. Although 100% of the revenues during the forecast period are derived from fixed-fee contracts and therefore not directly impacted by fluctuations in commodity prices,

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Antero Midstream may be indirectly impacted from changes in the Antero Resources development plan in response to fluctuations in commodity prices. Average forecasted prices for oil from 2018 through 2022 were assumed to be $55 per barrel, average forecasted prices for natural gas over the period were assumed to be $2.84 per MMBtu and average forecasted prices for C3+ NGLs over the period were assumed to be $38 per barrel;

•

Assumed debt financing for the cash consideration to be paid in connection with the Merger at the assumed weighted average rate of 5.5% per annum based on the observed yield to worst on Antero Midstream's outstanding 5.375% senior notes;

•

General and administrative cost savings of approximately $2.0 million per year; and

•

Tax savings of approximately $375 million from 2019 through 2022 for New AM relative to AMGP's projected tax expense under the status quo.

        In addition, at the request of the AM Conflicts Committee, Antero Management made available to the committees and their financial advisors a sensitivity analysis, which illustrated how the projected Antero Midstream and AMGP Status Quo information presented above would be impacted by certain "downside case" assumptions, which consisted of a decrease in Antero Resources' projected net production from (1) a compound annual growth rate of 20% from 2017 through 2020 to a compound annual growth rate of 17% over such period, and (2) approximately 15% net production growth in each of 2021 and 2022 to approximately 11% net production growth in such years.

        The projected financial information is based on numerous variables and assumptions that are inherently uncertain and are beyond the control of AMGP, Antero Midstream and Antero Resources, and the risk of inaccuracy increases with the length of the forecast period. Important factors that may affect actual results and cause the projected financial information not to be achieved include, but are not limited to, commodity price volatility, inflation, lack of availability of drilling and production equipment and services, environmental risks, drilling and other operating risks, regulatory changes, the uncertainty inherent in estimating natural gas and oil reserves and in projecting future rates of production, cash flow and access to capital, the timing of development expenditures, and the other risks described under the sections entitled "Special Note Regarding Forward-Looking Statements," "Special Factors" and "Risk Factors." In fact, the projections of future prices of oil, natural gas and NGLs have changed since the time these projections were made and are expected to remain volatile in the future. The projected financial information also reflects assumptions as to certain business decisions that are subject to change. As a result, actual results may differ materially from those contained in the projected financial information. Accordingly, there can be no assurance that the forecasted results will be realized and neither AMGP nor Antero Midstream undertakes any obligation to update or revise the projected financial information.

        The inclusion of the projected financial information in this joint proxy statement/prospectus should not be regarded as an indication that any of AMGP, Antero Midstream, or their respective officers, directors, partners, affiliates, advisors or other representatives considered the projected financial information to be necessarily predictive of actual future events, and the projected financial information should not be relied upon as such. None of AMGP, Antero Midstream or any of their respective officers, directors, partners, affiliates, advisors or other representatives can give you any assurance that actual results will not differ from the projected results. Neither AMGP nor Antero Midstream undertakes any obligation to update or otherwise revise or reconcile the projected financial information to reflect circumstances existing after the date the projected financial information was generated or to reflect the occurrence of future events in the event that any or all of the assumptions underlying the projections are shown to be in error or for any other reason. Neither AMGP nor Antero Midstream intends to make publicly available any update or other revision to the projected financial information. Neither AMGP nor Antero Midstream makes any representation to any AMGP Shareholder, AM Unitholder or any other person regarding AMGP's or Antero Midstream's performance compared to

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the information contained in the projected financial information or that projected results will be achieved. Neither AMGP nor Antero Midstream has made any representation in the Simplification Agreement or otherwise concerning the projected financial information.

Non-GAAP Financial Measures

Antero Midstream Status Quo and New AM Pro Forma Adjusted EBITDA and Distributable Cash Flow

        Antero Midstream uses Adjusted EBITDA as an important indicator of its performance. Antero Midstream defines Adjusted EBITDA as net income before interest expense, impairment of property and equipment, depreciation expense, accretion, equity-based compensation expense, excluding equity in earnings of unconsolidated affiliates, and including cash distributions from unconsolidated affiliates, and gain on sale of assets.

        Antero Midstream uses Adjusted EBITDA to assess:

•

the financial performance of its assets, without regard to financing methods in the case of Adjusted EBITDA, capital structure or historical cost basis;

•

its operating performance and return on capital as compared to other publicly traded partnerships in the midstream energy sector, without regard to financing or capital structure; and

•

the viability of acquisitions and other capital expenditure projects.

        Antero Midstream defines Distributable Cash Flow as Adjusted EBITDA less interest paid, income tax withholding payments and cash reserved for payments of income tax withholding upon vesting of equity-based compensation awards, cash reserved/paid for bond interest and ongoing maintenance capital expenditures paid. Antero Midstream uses Distributable Cash Flow as a performance metric to compare the cash generating performance of Antero Midstream from period to period and to compare the cash generating performance for specific periods to the cash distributions (if any) that are expected to be paid to AM Unitholders. Distributable Cash Flow does not reflect changes in working capital balances.

        Adjusted EBITDA and Distributable Cash Flow are non-GAAP financial measures. The GAAP measure most directly comparable to Adjusted EBITDA and Distributable Cash Flow is net income. The non-GAAP financial measures of Adjusted EBITDA and Distributable Cash Flow should not be considered as alternatives to the GAAP measure of net income. Adjusted EBITDA and Distributable Cash Flow are not presentations made in accordance with GAAP and have important limitations as an analytical tool because they include some, but not all, items that affect net income. You should not consider Adjusted EBITDA and Distributable Cash Flow in isolation or as a substitute for analyses of results as reported under GAAP. Antero Midstream's definition of Adjusted EBITDA and Distributable Cash Flow may not be comparable to similarly titled measures of other partnerships.

Antero Resources Stand-Alone Net Debt and Adjusted EBITDAX

        "Stand-Alone" data represents information for Antero Resources on an unconsolidated basis, reflecting Antero Resources' investment in Antero Midstream under the equity method of accounting. Antero Resources calculates Stand-Alone Net Debt as total debt less cash and cash equivalents, each on a stand-alone basis. Stand-Alone Adjusted EBITDAX as defined by Antero Resources represents income or loss as reported in the Parent column of Antero Resources' guarantor footnote to its financial statements before interest expense, interest income, gains or losses from commodity derivatives and marketing derivatives, but including net cash receipts or payments on derivative instruments included in derivative gains or losses, income taxes, impairments, depletion, depreciation, amortization, and accretion, exploration expense, equity-based compensation, gain or loss on early

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extinguishment of debt, gain or loss on sale of assets, equity in earnings or loss of Antero Midstream and gain or loss on changes in the fair value of contingent acquisition consideration. Stand-Alone Adjusted EBITDAX also includes distributions received from limited partner interests in Antero Midstream common units.

Opinion of the AMGP Conflicts Committee's Financial Advisor

        Goldman Sachs rendered to the AMGP Conflicts Committee its oral opinion, which was subsequently confirmed by delivery of a written opinion, dated October 9, 2018, that, as of the date of such written opinion and based upon and subject to the factors and assumptions set forth therein, after giving effect to the issuance of shares of New AM Common Stock pursuant to the Series B Exchange, the Aggregate Consideration (as defined in such opinion) to be paid by AMGP for the AM Common Units pursuant to the Simplification Agreement was fair from a financial point of view to AMGP.

The full text of the written opinion of Goldman Sachs, dated October 9, 2018, which sets forth assumptions made, procedures followed, matters considered and limitations on the review undertaken in connection with the opinion, is attached as Annex C. Goldman Sachs provided advisory services and its opinion for the information and assistance of the AMGP Conflicts Committee in connection with its consideration of the Transactions. The Goldman Sachs opinion is not a recommendation as to how any holder of AMGP Common Shares should vote with respect to the Transactions, or any other matter.

        In connection with rendering the opinion described above and performing its related financial analyses, Goldman Sachs reviewed, among other things:

•

the Simplification Agreement;

•

the Annual Report on Form 10-K of AMGP for the year ended December 31, 2017;

•

AMGP's Registration Statement on Form S-1, including the prospectus contained therein, dated May 3, 2017, relating to AMGP's initial public offering of certain of its securities;

•

the Annual Reports on Form 10-K of Antero Midstream for the four years ended December 31, 2017;

•

Antero Midstream's Registration Statement on Form S-1, including the prospectus contained therein, dated November 4, 2014, relating to Antero Midstream's initial public offering of certain of its securities;

•

certain interim reports to AMGP Shareholders and AM Unitholders and Quarterly Reports on Form 10-Q of AMGP and Antero Midstream, respectively;

•

certain other communications from AMGP and Antero Midstream to their respective shareholders and unitholders;

•

certain publicly available research analyst reports for AMGP and Antero Midstream;

•

certain financial analyses and forecasts for Antero Midstream (which we refer to in this section as the "Midstream Forecast"), certain financial analyses and forecasts for AMGP standalone (which we refer to in this section as the "GP Standalone Forecast") and certain financial analyses and forecasts for AMGP pro forma for the Transactions (which we refer to in this section as the "AMGP Pro Forma Forecast" and, together with the Midstream Forecast and the AMGP Standalone Forecast, as the "Forecasts"), in each case, as prepared by the management of Antero Resources and approved for Goldman Sachs' use by the AMGP Conflicts Committee, including certain tax step-up benefits projected to result from the Transactions as provided by the management of Antero Resources and approved for Goldman Sachs' use by the AMGP Conflicts Committee (which we refer to in this section as the "Tax Benefits Forecast").

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        Goldman Sachs also held discussions with members of the AMGP Conflicts Committee and the management of Antero Resources regarding their respective assessment of the past and current business operations, financial condition and future prospects of AMGP and Antero Midstream and the strategic rationale for, and the potential benefits of, the Transactions; reviewed the reported price and trading activity for the AMGP Common Shares and the AM Common Units; compared certain financial and stock market information for AMGP and Antero Midstream with similar information for certain other companies the securities of which are publicly traded; reviewed the financial terms of certain recent business combinations in the midstream oil and gas industry; and performed such other studies and analyses, and considered such other factors, as it deemed appropriate.

        For purposes of rendering this opinion, Goldman Sachs, with the AMGP Conflicts Committee's consent, relied upon and assumed the accuracy and completeness of all of the financial, legal, regulatory, tax, accounting and other information provided to, discussed with or reviewed by, it, without assuming any responsibility for independent verification thereof. In that regard, Goldman Sachs assumed with the AMGP Conflicts Committee's consent that the Forecasts, including the Tax Benefits Forecast, were reasonably prepared on a basis reflecting the best currently available estimates and judgments of the AMGP Conflicts Committee. Goldman Sachs did not make an independent evaluation or appraisal of the assets and liabilities (including any contingent, derivative or other off-balance-sheet assets and liabilities) of AMGP or Antero Midstream or any of their respective subsidiaries and it was not furnished with any such evaluation or appraisal. Goldman Sachs assumed that all governmental, regulatory or other consents and approvals necessary for the consummation of the Transactions will be obtained without any adverse effect on AMGP or Antero Midstream or on the expected benefits of the Transactions in any way meaningful to its analysis. Goldman Sachs has also assumed that the Transactions, including the Series B Exchange, will be consummated on the terms set forth in the Simplification Agreement without the waiver or modification of any term or condition the effect of which would be in any way meaningful to its analysis.

        Goldman Sachs' opinion does not address the underlying business decision of AMGP to engage in the Transactions, or the relative merits of the Transactions as compared to any strategic alternatives that may be available to AMGP; nor does it address any legal, regulatory, tax or accounting matters. Goldman Sachs' opinion addresses only the fairness from a financial point of view to AMGP, as of the date of the opinion and after giving effect to the issuance of shares of New AM Common Stock pursuant to the Series B Exchange, of the Aggregate Consideration to be paid by AMGP for the AM Common Units pursuant to the Simplification Agreement. Goldman Sachs' opinion does not express any view on, and does not address, any other term or aspect of the Simplification Agreement or Transactions or any term or aspect of any other agreement or instrument contemplated by the Simplification Agreement or entered into or amended in connection with the Transactions, including, the Series B Exchange, the contribution of New AM Common Stock to NewCo, the Conversion, the GP Merger, any allocation of the Aggregate Consideration or the fairness of the Transactions to, or any consideration received in connection therewith by, the holders of any class of securities, creditors, or other constituencies of AMGP; nor as to the fairness of the amount or nature of any compensation to be paid or payable to any of the officers, directors or employees of AMGP or Antero Midstream, or any class of such persons in connection with the Transactions, whether relative to the Aggregate Consideration to be paid by AMGP for the AM Common Units pursuant to the Simplification Agreement or otherwise. Goldman Sachs' opinion was necessarily based on economic, monetary, market and other conditions as in effect on, and the information made available to it as of, the date of the opinion and Goldman Sachs assumed no responsibility for updating, revising or reaffirming its opinion based on circumstances, developments or events occurring after the date of its opinion. In addition, Goldman Sachs does not express any opinion as to the prices at which the shares of New AM Common Stock will trade at any time or as to the impact of the Transactions on the solvency or viability of AMGP or Antero Midstream or the ability of AMGP or Antero Midstream to pay their

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respective obligations when they come due. Goldman Sachs' opinion was approved by a fairness committee of Goldman Sachs.

        The following is a summary of the material financial analyses delivered by Goldman Sachs to the AMGP Conflicts Committee in connection with rendering the opinion described above. The following summary, however, does not purport to be a complete description of the financial analyses performed by Goldman Sachs, nor does the order of analyses described represent relative importance or weight given to those analyses by Goldman Sachs. Some of the summaries of the financial analyses include information presented in tabular format. The tables must be read together with the full text of each summary and are alone not a complete description of Goldman Sachs' financial analyses. Except as otherwise noted, the following quantitative information, to the extent that it is based on market data, is based on market data as it existed on or before October 5, 2018, the last trading day before the meeting of the AMGP Conflicts Committee that approved the Transactions, and is not necessarily indicative of current market conditions.

        Implied Exchange Ratio Analysis.    Historical Stock Trading Analysis. Goldman Sachs reviewed the historical trading prices for the AMGP Common Shares and the AM Common Units from May 4, 2017 (the date of the AMGP initial public offering) to October 5, 2018 and calculated historical exchange ratios for the AM Common Units by dividing the closing price per AM Common Unit by the closing price per AMGP Common Share for the following periods: (i) May 4, 2017 through October 5, 2018; (ii) January 1, 2018 through October 5, 2018; (iii) January 26, 2018, the last trading day prior to the announcement by Antero Resources that it was working with legal and financial advisors to evaluate potential measures to address the discount in its trading value (which we refer to in this section as "the last undisturbed trading day"), through October 5, 2018; (iv) February 23, 2018, the last trading day prior to the announcement by Antero Resources, Antero Midstream, and AMGP of the formation of committees of their respective boards of directors to evaluate potential measures related to their respective companies' valuations, through October 5, 2018; and (v) the 90-trading day, 60-trading day and 30-trading day periods ended October 5, 2018. The following table presents the results of this analysis:

Period ending October 5, 2018	Historical Exchange Ratio
Since May 4, 2017 (AMGP initial public offering)		1.5809x
Since January 1, 2018		1.5819x
Since the last undisturbed trading day		1.5915x
Since last trading day prior to February 23, 2018 (announcement of formation of committees)		1.6133x
Last 90 trading days		1.6605x
Last 60 trading days		1.6904x
Last 30 trading days		1.7252x

        Implied Consideration and Premia Analysis.    Goldman Sachs analyzed illustrative implied values of the Aggregate Consideration per AM Common Unit to be paid by AMGP pursuant to the Simplification Agreement in relation to: (i) the closing price per AM Common Unit as of October 5, 2018; (ii) the volume-weighted average price, which we refer to in this section as the "VWAP," per AM Common Unit for the thirty trading day period ended October 5, 2018; (iii) the closing price per AM Common Unit as of the last undisturbed trading day; and (iv) the VWAP per AM Common Unit for the thirty trading day period ended on the last undisturbed trading day. To calculate the illustrative implied values of the Aggregate Consideration Goldman Sachs added the illustrative blended cash consideration of $3.18 to be paid by AMGP for each AM Common Unit pursuant to the Simplification Agreement (the "Blended Cash Consideration") to the product obtained by multiplying the closing price or VWAP of the AMGP Common Shares for the relevant date or period by an illustrative

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blended equity exchange ratio of 1.6189 shares of New AM Common Stock to be paid by AMGP for each AM Common Unit pursuant to the Simplification Agreement (the "Blended Equity Exchange Ratio"). The Blended Cash Consideration was approved for Goldman Sachs' use by the AMGP Conflicts Committee and was calculated using the standard cash consideration for AM Public Unitholders of $3.415, the standard cash consideration for Antero Resources of $3.00, the aggregate number of outstanding AM Common Units held by the AM Public Unitholders as provided by the AMGP Conflicts Committee, the aggregate number of outstanding AM Common Units held by Antero Resources as provided by the AMGP Conflicts Committee and the aggregate number of AM Common Units reserved for issuance under the AM LTIP as provided by the AMGP Conflicts Committee. References to "standard cash consideration" are to the cash component of the applicable Mixed Consideration Election. The Blended Equity Exchange Ratio was approved for Goldman Sachs' use by the AMGP Conflicts Committee and was calculated using the standard New AM Common Stock consideration equity exchange ratio for AM Public Unitholders of 1.6350 shares of New AM Common Stock for each AM Common Unit, the Antero Resources exchange ratio of 1.6023, an illustrative AM LTIP exchange ratio of 1.8326 (calculated using the standard New AM Common Stock consideration equity exchange ratio for AM Public Unitholders of 1.6350 shares of New AM Common Stock for each AM Common Unit, the standard cash consideration for AM Public Unitholders of $3.415 and the 20-day VWAP of the AMGP Common Shares as of October 5, 2018), the aggregate number of outstanding AM Common Units held by the AM Public Unitholders as provided by the AMGP Conflicts Committee, the aggregate number of outstanding AM Common Units held by Antero Resources as provided by the AMGP Conflicts Committee, the aggregate number of AM Common Units reserved for issuance under the AM LTIP as provided by the AMGP Conflicts Committee and the closing price per AMGP Common Share as of October 5, 2018. The following table presents the results of this analysis:

AM Common Unit Metric	Implied Value of Aggregate Consideration		Implied Premia
Closing price as of October 5, 2018	$	31.53		6	%
30-day VWAP ended October 5, 2018	$	31.20		5	%
Closing price as of last undisturbed trading day	$	38.83		17	%
30-day VWAP ended on last undisturbed trading day	$	35.44		17	%

        Selected Transactions Analysis.    Goldman Sachs reviewed and analyzed, using publicly available information, the acquisition premia or discount for buy-in transactions involving MLPs announced during the time period from October 2013 through October 5, 2018. For the entire period, using publicly available information, Goldman Sachs calculated the discount / premia of the price paid in the transactions relative to the target's last undisturbed closing stock price prior to announcement of the relevant transaction, offer, or strategic review, as applicable, and the VWAP for the thirty trading day period ended on the target's last undisturbed trading day prior to announcement of the relevant transaction, offer or strategic review, as applicable. This analysis indicated a range of illustrative discount / premia of (9)% to 26% using the price paid in the transactions relative to the target's last undisturbed closing stock price prior to announcement of the relevant transaction, offer or strategic review, as applicable, and a range of illustrative discount / premia of 2% to 27% using the price paid in the transactions relative to the target's 30 trading day VWAP ended on the target's last undisturbed trading day prior to announcement of the relevant transaction, offer or strategic review, as applicable.

Illustrative Discounted Distributable Cash Flow Analysis—AMGP Standalone.

        Using the AMGP Standalone Forecast, Goldman Sachs performed an illustrative discounted distributable cash flow analysis of the AMGP Common Shares on a standalone basis. Using discount rates ranging from 8.0% to 10.0%, reflecting estimates of AMGP's cost of equity, Goldman Sachs

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discounted to present value as of September 30, 2018 (i) estimates of distributable cash flow per AMGP Common Share for October 1, 2018 through December 31, 2022, as reflected in the AMGP Standalone Forecast and (ii) a range of illustrative terminal values for AMGP, which were calculated by applying perpetuity growth rates ranging from 1.5% to 3.0% to a terminal year estimate of the distributable cash flow per AMGP Common Share, as reflected in the AMGP Standalone Forecast (which analysis implied exit terminal year yields of 4.9% to 8.3%). Goldman Sachs derived such discount rates by application of the Capital Asset Pricing Model, which requires certain company-specific inputs, including a beta for the company, as well as certain financial metrics for the United States financial markets generally. The range of perpetuity growth rates was estimated by Goldman Sachs utilizing its professional judgment and experience, taking into account the AMGP Standalone Forecast and market expectations regarding long-term real growth of gross domestic product and inflation. Goldman Sachs then derived ranges of illustrative value per AMGP Common Share on a standalone basis by adding the ranges of illustrative values it derived using the estimated distributable cash flows per AMGP Common Share and the illustrative terminal values, as described above. This analysis resulted in a range of illustrative equity values per AMGP Common Share on a standalone basis of $23.56 to $39.53.

Illustrative Discounted Distributable Cash Flow Analysis—AMGP Pro Forma.

        Using the AMGP Pro Forma Forecast, Goldman Sachs performed an illustrative discounted distributable cash flow analysis of the AMGP Common Shares pro forma for the Transactions. Using discount rates ranging from 8.0% to 10.0%, reflecting estimates of the pro forma AMGP's cost of equity, Goldman Sachs discounted to present value as of September 30, 2018 (i) estimates of distributable cash flow per AMGP Common Share pro forma for the Transactions for October 1, 2018 through December 31, 2022, as reflected in the AMGP Pro Forma Forecast and (ii) a range of illustrative terminal values for AMGP pro forma for the Transactions, which were calculated by applying perpetuity growth rates ranging from 1.5% to 3.0% to a terminal year estimate of the distributable cash flow per AMGP Common Share, as reflected in the AMGP Pro Forma Forecast (which analysis implied exit terminal year yields of 4.9% to 8.3%), and (iii) estimates of cash tax savings to AMGP pro forma for the Transactions for January 1, 2023 through December 31, 2033, as reflected in the Tax Benefits Forecast. Goldman Sachs derived such discount rates by application of the Capital Asset Pricing Model, which requires certain company-specific inputs, including a beta for the company, as well as certain financial metrics for the United States financial markets generally. The range of perpetuity growth rates was estimated by Goldman Sachs utilizing its professional judgment and experience, taking into account the AMGP Pro Forma Forecast and market expectations regarding long-term real growth of gross domestic product and inflation. Goldman Sachs then derived a range of illustrative values per AMGP Common Share pro forma for the Transactions by adding the ranges of illustrative values it derived using the estimated distributable cash flows per AMGP Common Share, the illustrative terminal values and the estimated cash tax savings, as described above. This analysis resulted in a range of illustrative equity values per AMGP Common Share pro forma for the Transactions of $26.73 to $42.78.

Illustrative Present Value of Future Share Price Analysis—AMGP Standalone.

        Goldman Sachs performed an illustrative analysis of the implied present values of illustrative future values per AMGP Common Share on a standalone basis, which is designed to provide an indication of the present value of a theoretical future value of a company's equity as a function of such company's financial multiples. For this analysis, Goldman Sachs used the AMGP Standalone Forecast for the period October 1, 2018 through December 31, 2018 and each of the years 2019 through 2021. Goldman Sachs first calculated the implied values per AMGP Common Share on a standalone basis as of December 31 for each of the years 2019 to 2021 by applying a range of illustrative one-year forward P/DCF multiples of 13.3 to 16.7 to estimate distributable cash flow per AMGP Common Share for each

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of the years 2020 to 2022, as reflected in the AMGP Standalone Forecast, which are referred to in this section as the "2020 AMGP Standalone DCF Estimate", the "2021 AMGP Standalone DCF Estimate" and the "2022 AMGP Standalone DCF Estimate", respectively. The illustrative multiple estimates were derived by Goldman Sachs utilizing its professional judgment and experience, taking into account current and historical trading data and illustrative current one-year P/DCF multiples and illustrative implied distribution yields for AMGP, Antero Midstream, and certain other publicly traded corporations in the U.S. midstream oil and gas industry. Goldman Sachs then discounted to present value as of September 30, 2018, using an illustrative discount rate of 9.0%, reflecting an estimate of AMGP's cost of equity, (i) the sum of (x) the illustrative equity value it derived for AMGP as of December 31, 2019 and (y) the aggregate per share dividends estimated for October 1, 2018 through December 31, 2019 as reflected in the AMGP Standalone Forecast; (ii) the sum of (x) the illustrative equity value it derived for AMGP as of December 31, 2020 and (y) the aggregate per share dividends estimated for October 1, 2018 through December 31, 2020 as reflected in the AMGP Standalone Forecast; and (iii) the sum of (x) the illustrative equity value it derived for AMGP as of December 31, 2021 and (y) the aggregate per share dividends estimated for October 1, 2018 through December 31, 2021 as reflected in the AMGP Standalone Forecast. Goldman Sachs derived such discount rate by application of the Capital Asset Pricing Model, which requires certain company-specific inputs, including a beta for the company, as well as certain financial metrics for the United States financial markets generally. This analysis resulted in a range of illustrative implied present values per AMGP Common Share of (i) $17.02 to $21.03 using the 2020 AMGP Standalone DCF Estimate, (ii) $21.27 to $26.05 using the 2021 AMGP Standalone DCF Estimate and (iii) $25.90 to $31.49 using the 2022 AMGP Standalone DCF Estimate.

Illustrative Present Value of Future Share Price Analysis—AMGP Pro Forma.

        Goldman Sachs performed an illustrative analysis of the implied present values of illustrative future values per AMGP Common Share pro forma for the Transactions, which is designed to provide an indication of the present value of a theoretical future value of a company's equity as a function of such company's financial multiples. For this analysis, Goldman Sachs used the AMGP Pro Forma Forecast for the period October 1, 2018 through December 31, 2018 and each of the years 2019 through 2021. Goldman Sachs first calculated the implied values per AMGP Common Share pro forma for the Transactions as of December 31 for each of the years 2019 to 2021 by applying a range of illustrative one-year forward P/DCF multiples of 11.0 to 14.0 to estimated distributable cash flow per AMGP Common Share for each of the years 2020 to 2022, as reflected in the AMGP Pro Forma Forecast, which are referred to in this section as the "2020 AMGP Pro Forma DCF Estimate", the "2021 AMGP Pro Forma DCF Estimate" and the "2022 AMGP Pro Forma DCF Estimate", respectively. The illustrative multiple estimates were derived by Goldman Sachs utilizing its professional judgment and experience, taking into account current and historical trading data and illustrative current one-year P/DCF multiples and illustrative implied distribution yields for AMGP, Antero Midstream and certain other publicly traded corporations in the U.S. midstream oil and gas industry. Goldman Sachs then discounted to present value as of September 30, 2018, using an illustrative discount rate of 9.0%, reflecting an estimate of AMGP's cost of equity, (i) the sum of (x) the illustrative equity value it derived for AMGP pro forma for the Transactions as of December 31, 2019 and (y) the aggregate per share dividends estimated for October 1, 2018 through December 31, 2019 as reflected in the AMGP Pro Forma Forecast; (ii) the sum of (x) the illustrative equity value it derived for AMGP pro forma for the Transactions as of December 31, 2020 and (y) the aggregate per share dividends estimated for October 1, 2018 through December 31, 2020 as reflected in the AMGP Pro Forma Forecast; and (iii) the sum of (x) the illustrative equity value it derived for AMGP pro forma for the Transactions as of December 31, 2021 and (y) the aggregate per share dividends estimated for October 1, 2018 through December 31, 2021 as reflected in the AMGP Pro Forma Forecast. Goldman Sachs derived such discount rate by application of the Capital Asset Pricing Model, which requires certain company-

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specific inputs, including a beta for the company, as well as certain financial metrics for the United States financial markets generally. This analysis resulted in a range of illustrative implied present values per AMGP Common Share pro forma for the Transactions of (i) $20.79 to $26.10 using the 2020 AMGP Pro Forma DCF Estimate, (ii) $24.23 to $30.11 using the 2021 AMGP Pro Forma DCF Estimate and (iii) $27.01 to $33.22 using the 2022 AMGP Pro Forma DCF Estimate.

Illustrative Discounted Distribution Analysis—Antero Midstream Standalone.

        Using the Midstream Forecast, Goldman Sachs performed an illustrative discounted distribution analysis of the AM Common Units on a standalone basis. Using discount rates ranging from 8.0% to 10.0%, reflecting estimates of Antero Midstream's cost of equity, Goldman Sachs discounted to present value as of September 30, 2018 (i) estimates of distributions per AM Common Unit for October 1, 2018 through December 31, 2022, as reflected in the Midstream Forecast, (ii) a range of illustrative terminal values for Antero Midstream, which were calculated by applying perpetuity growth rates ranging from 1.5% to 3.0% to a terminal year estimate of the distributions per AM Common Unit, as reflected in the Midstream Forecast (which analysis implied exit terminal year yields of 4.9% to 8.3%). Goldman Sachs derived such discount rates by application of the Capital Asset Pricing Model, which requires certain company-specific inputs, including a beta for the company, as well as certain financial metrics for the United States financial markets generally. The range of perpetuity growth rates was estimated by Goldman Sachs utilizing its professional judgment and experience, taking into account the Midstream Forecast and market expectations regarding long-term real growth of gross domestic product and inflation. Goldman Sachs then derived ranges of illustrative value per AM Common Unit on a standalone basis by adding the ranges of illustrative values it derived using the estimated distributions per AM Common Unit and the illustrative terminal values, as described above. This analysis resulted in a range of illustrative equity values per AM Common Unit on a standalone basis of $44.67 to $74.16.

Illustrative Present Value of Future Share Price Analysis—Antero Midstream Standalone.

        Goldman Sachs performed an illustrative analysis of the implied present values of illustrative future values per AM Common Unit on a standalone basis, which is designed to provide an indication of the present value of a theoretical future value of a company's equity as a function of such company's financial ratios. For this analysis, Goldman Sachs used the Midstream Forecast for the period October 1, 2018 through December 31, 2018 and each of the years 2019 through 2021. Goldman Sachs first calculated the implied values per AM Common Unit on a standalone basis as of December 31 for each of the years 2019 to 2021 by applying a range of illustrative one-year forward distribution yields of 7.0% to 8.0% to estimated distributions per AM Common Unit for each of the years 2020 to 2022, as reflected in the Midstream Forecast, which are referred to in this section as the "2020 Antero Midstream Standalone Distributions Estimate", the "2021 Antero Midstream Standalone Distributions Estimate" and the "2022 Antero Midstream Standalone Distributions Estimate", respectively. The illustrative distribution yield estimates were derived by Goldman Sachs utilizing its professional judgment and experience, taking into account current and historical trading data and illustrative current one-year distribution yields for AMGP, Antero Midstream, and certain other publicly traded master limited partnerships in the U.S. midstream oil and gas industry. Goldman Sachs then discounted to present value as of September 30, 2018, using an illustrative discount rate of 9.0%, reflecting an estimate of Antero Midstream's cost of equity, (i) the sum of (x) the illustrative equity value it derived for Antero Midstream as of December 31, 2019 and (y) the aggregate per share distributions estimated for October 1, 2018 through December 31, 2019 as reflected in the Midstream Forecast; (ii) the sum of (x) the illustrative equity value it derived for Antero Midstream as of December 31, 2020 and (y) the aggregate per share distributions for October 1, 2018 through December 31, 2020 as reflected in the Midstream Forecast; and (iii) the sum of (x) the illustrative equity value it derived for Antero Midstream as of December 31, 2021 and (y) the aggregate per share distributions estimated for October 1, 2018 through December 31, 2021 as reflected in the Midstream Forecast. Goldman Sachs

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derived such discount rate by application of the Capital Asset Pricing Model, which requires certain company-specific inputs, including a beta for the company, as well as certain financial metrics for the United States financial markets generally. This analysis resulted in a range of illustrative implied present values per AM Common Unit of (i) $34.52 to $39.09 using the 2020 Antero Midstream Standalone Distributions Estimate, (ii) $40.20 to $45.23 using the 2021 Antero Midstream Standalone Distributions Estimate and (iii) $46.41 to $51.94 using the 2022 Antero Midstream Standalone Distributions Estimate.

        Illustrative Contribution Analysis.    Goldman Sachs analyzed the implied contribution of the AMGP Common Shares, the Series B Units and AM Common Units to the pro forma combined company based on the standalone dividends / distributions, current equity values and illustrative equity values for each of the AMGP Common Shares, the Series B Units and the AM Common Units using (i) estimated dividends to the AMGP Common Shares and estimated distributions to the Series B Units and the AM Common Units for 2018 to 2022, as reflected in the Forecasts, (ii) illustrative aggregate equity values for the AMGP Common Shares, the Series B Units and the AM Common Units, calculated using closing trading prices of the AMGP Common Shares and the AM Common Units as of October 5, 2018 (and, in the case of the AM Common Units both including and excluding an illustrative present value of the tax synergies reflected in the Tax Benefits Forecast), and an estimated equity value for the Series B Units calculated using the number of outstanding Series B Units and the estimated fair value per Series B Unit each as disclosed by AMGP in its Quarterly Report on Form 10-Q for the quarter ended June 30, 2018, (iii) illustrative pro rata equity ownership in New AM based on the number of shares of New AM Common Stock to be issued to holders of AMGP Common Shares, the number of shares of New AM Common Stock to be paid to the Series B Holders in the Series B Exchange, and the implied number of shares of New AM Common Stock to be paid to holders of AM Common Units based on the illustrative blended aggregate consideration exchange ratio of 1.8004 shares of New AM Common Stock to be paid by AMGP for each AM Common Unit pursuant to the Simplification Agreement (the "Blended Aggregate Consideration Exchange Ratio"), (iv) the illustrative implied aggregate value of AMGP based on the number of AMGP Common Shares outstanding and the illustrative implied values per AMGP Common Share derived using the Illustrative Discounted Distributable Cash Flow Analysis—AMGP Standalone described above, the illustrative implied aggregate value of Antero Midstream based on the number of AM Common Units outstanding, including under the AM LTIP, and the illustrative implied values per AM Common Unit derived using the Illustrative Discounted Distribution Analysis—Antero Midstream Standalone described above and an estimated equity value for the Series B Units calculated using the number of outstanding Series B Units and the estimated fair value per Series B Unit each as disclosed by AMGP in its Quarterly Report on Form 10-Q for the quarter ended June 30, 2018 and (v) the illustrative implied aggregate value of AMGP based on the number of AMGP Common Shares outstanding and the illustrative implied present values per AMGP Common Share derived using the Illustrative Present Value of Future Share Price Analysis—AMGP Standalone described above, the illustrative implied aggregate value of Antero Midstream based on the number of AM Common Units outstanding, including under the AM LTIP, and the illustrative implied present values per AM Common Unit derived by using the Illustrative Present Value of Future Share Price Analysis—Antero Midstream Standalone described above and an estimated equity value for the Series B Units calculated using the number of outstanding Series B Units and the estimated fair value per Series B Unit each as disclosed by AMGP in its Quarterly Report on Form 10-Q for the quarter ended June 30, 2018. The Blended Aggregate Consideration Exchange Ratio was approved for Goldman Sachs' use by the AMGP Conflicts Committee and was calculated using the standard New AM Common Stock consideration equity exchange ratio for AM Public Unitholders of 1.6350 shares of New AM Common Stock for each AM Common Unit, the standard cash consideration for AM Public Unitholders of $3.415, the Antero Resources exchange ratio of 1.6023, the standard cash consideration for Antero Resources of $3.00, an illustrative AM LTIP exchange ratio of 1.8326, the aggregate number of outstanding AM Common

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Units held by the AM Public Unitholders as provided by the AMGP Conflicts Committee, the aggregate number of outstanding AM Common Units held by Antero Resources as provided by the AMGP Conflicts Committee, the aggregate number of AM Common Units reserved for issuance under the AM LTIP as provided by the AMGP Conflicts Committee and the closing price per AMGP Common Share as of October 5, 2018.

        The following table presents the results of this analysis:

	AMGP Common Shares			Series B Units			AM Common Units
Dividends / Distributions
FY 2018 Distributions		23.4	%		1.6	%		75.0	%
FY 2019 Distributions		28.0	%		2.1	%		70.0	%
FY 2020 Distributions		31.1	%		2.4	%		66.5	%
FY 2021 Distributions		32.7	%		2.6	%		64.6	%
FY 2022 Distributions		34.1	%		2.8	%		63.2	%
Public Equity Values
Equity Value		36.1	%		2.0	%		61.9	%
Equity Value including Tax Synergies		33.1	%		2.0	%		65.0	%
Equity Value implied by Blended Aggregate Consideration Exchange Ratio		36.6	%		3.4	%		59.9	%
Discounted DCF / Distribution Analyses
Low Discounted Value		33.8	%		1.4	%		64.8	%
High Discounted Value		34.2	%		0.8	%		64.9	%
AMGP and Antero Midstream Present Value of Future Share Price Analyses
Low PV of Future Share Price		32.2	%		1.9	%		66.0	%
High PV of Future Share Price		37.1	%		1.2	%		61.8	%

        Pro Forma Merger Analysis.    Goldman Sachs prepared illustrative pro forma analyses of the potential financial impact of the Merger using the AMGP Standalone Forecast and the AMGP Pro Forma Forecast. For each of the calendar years 2019 to 2022 Goldman Sachs compared the distributable cash flows per AMGP Common Share and the dividends per AMGP Common Share, on a standalone basis, to the distributable cash flows per AMGP Common Share and the dividends per AMGP Common Share pro forma for the Transactions. The following table presents the results of this analysis, which indicated the Transactions would be accretive to AMGP on the basis of distributable cash flows per AMGP Common Share and dividends per AMGP Common Share:

Metric	2019		2020		2021		2022
Distributable cash flows per share standalone	$	0.89	$	1.34	$	1.74	$	2.22
Distributable cash flows per share pro forma	$	1.62	$	1.97	$	2.38	$	2.74
Dividends per share standalone	$	0.89	$	1.34	$	1.74	$	2.22
Dividends per share pro forma	$	1.24	$	1.60	$	1.93	$	2.31

        The preparation of a fairness opinion is a complex process and is not necessarily susceptible to partial analysis or summary description. Selecting portions of the analyses or of the summary set forth above, without considering the analyses as a whole, could create an incomplete view of the processes underlying Goldman Sachs' opinion. In arriving at its fairness determination, Goldman Sachs considered the results of all of its analyses and did not attribute any particular weight to any factor or analysis considered by it. Rather, Goldman Sachs made its determination as to fairness on the basis of its experience and professional judgment after considering the results of all of its analyses. No company

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or transaction used in the above analyses as a comparison is directly comparable to AMGP or Antero Midstream or the contemplated transaction.

        Goldman Sachs prepared these analyses for purposes of Goldman Sachs' providing its opinion to the AMGP Conflicts Committee as to the fairness from a financial point of view to AMGP, as of the date of the opinion and after giving effect to the issuance of shares of New AM Common Stock pursuant to the Series B Exchange, of the Aggregate Consideration to be paid by AMGP for the AM Common Units pursuant to the Simplification Agreement. These analyses do not purport to be appraisals nor do they necessarily reflect the prices at which businesses or securities actually may be sold. Analyses based upon forecasts of future results are not necessarily indicative of actual future results, which may be significantly more or less favorable than suggested by these analyses. Because these analyses are inherently subject to uncertainty, being based upon numerous factors or events beyond the control of the parties or their respective advisors, none of AMGP, Antero Midstream, Goldman Sachs or any other person assumes responsibility if future results are materially different from those forecast.

        The merger consideration was determined through arm's-length negotiations between the AMGP Conflicts Committee, the AM Conflicts Committee and AR Special Committee and was approved by the AMGP Board. Goldman Sachs provided advice to the AMGP Conflicts Committee during these negotiations. Goldman Sachs did not, however, recommend any specific exchange ratio or amount of consideration to AMGP GP or the AMGP Board or that any specific exchange ratio or amount of consideration constituted the only appropriate exchange ratio and/or amount of consideration for the transaction.

        As described above, Goldman Sachs' opinion to the AMGP Conflicts Committee was one of many factors taken into consideration by the AMGP Conflicts Committee in making its determination to approve the Simplification Agreement. The foregoing summary does not purport to be a complete description of the analyses performed by Goldman Sachs in connection with the fairness opinion and is qualified in its entirety by reference to the written opinion of Goldman Sachs attached as Annex C.

        Goldman Sachs and its affiliates are engaged in advisory, underwriting and financing, principal investing, sales and trading, research, investment management and other financial and non-financial activities and services for various persons and entities. Goldman Sachs and its affiliates and employees, and funds or other entities they manage or in which they invest or have other economic interests or with which they co-invest, may at any time purchase, sell, hold or vote long or short positions and investments in securities, derivatives, loans, commodities, currencies, credit default swaps and other financial instruments of AMGP GP, AMGP and Antero Midstream and any of their respective affiliates and third parties, including (i) Antero Resources, an affiliate of AMGP GP, AMGP and Antero Midstream, and (ii) Warburg Pincus LLC, an affiliate of significant shareholders of AMGP, or any currency or commodity that may be involved in the transaction contemplated by the Simplification Agreement, including the Series B Exchange. Goldman Sachs acted as financial advisor to the AMGP Conflicts Committee in connection with, and participated in certain of the negotiations leading to, the transaction contemplated by the Simplification Agreement. Goldman Sachs has provided certain financial advisory and/or underwriting services to AMGP and/or its affiliates from time to time for which the Investment Banking Division of Goldman Sachs has received, and may receive, compensation, including having acted as joint bookrunner with respect to an initial public offering of 37,250,000 common shares representing limited partner interests in AMGP in May 2017. During the two year period ended October 9, 2018, Goldman Sachs has recognized compensation for financial advisory and/or underwriting services provided by its Investment Banking Division to AMGP and/or its affiliates of approximately $2.7 million. Goldman Sachs also has provided certain financial advisory and/or underwriting services to Warburg Pincus LLC and/or its affiliates and portfolio companies from time to time for which the Investment Banking Division of Goldman Sachs has received, and may receive, compensation, including having acted as joint bookrunner with respect to an initial public

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offering of 72,100,000 American depositary shares of ZTO Express Inc., a portfolio company of Warburg Pincus LLC, in October 2016; as financial advisor to an affiliate of Warburg Pincus LLC in connection with its acquisition of ARA Asset Management in April 2017; as joint bookrunner with respect to a bank loan (aggregate principal amount $1,697,000,000) for The Endurance International Group, Inc., a portfolio company of Warburg Pincus LLC, in June 2017; as joint bookrunner with respect to the offering by Sotera Health LLC, a portfolio company of Warburg Pincus LLC, of 8.125% Senior Notes due 2021 (aggregate principal amount $75,000,000) in November 2017; as bookrunner with respect to an initial public offering of 4,000,000 American depositary shares of Cango Inc., a portfolio company of Warburg Pincus LLC, in July 2018; and as financial advisor to Kosmos Energy Ltd., a portfolio company of Warburg Pincus LLC, in connection with its acquisition of Deep Gulf Energy LP in August 2018. During the two year period ended October 9, 2018, Goldman Sachs has recognized compensation for financial advisory and/or underwriting services provided by its Investment Banking Division to Warburg Pincus LLC and/or its affiliates and portfolio companies of $54.0 million. Goldman Sachs may also in the future provide financial advisory and/or underwriting services to AMGP GP, AMGP, Antero Midstream, Antero Resources, Warburg Pincus LLC and their respective affiliates and portfolio companies, as applicable, for which the Investment Banking Division of Goldman Sachs may receive compensation. Goldman Sachs or its affiliates also may have co-invested with Warburg Pincus LLC and/or its affiliates from time to time and may have invested in limited partnership units of affiliates of Warburg Pincus LLC from time to time and may do so in the future.

        The AMGP Conflicts Committee selected Goldman Sachs as its financial advisor because it is an internationally recognized investment banking firm that has substantial experience in transactions similar to the Transactions. Pursuant to a letter agreement dated March 9, 2018 the AMGP Conflicts Committee engaged Goldman Sachs to act as its financial advisor in connection with the contemplated transaction. The engagement letter between the AMGP Conflicts Committee and Goldman Sachs provides for a transaction fee that is estimated, based on the information available as of the date of announcement, at approximately $4,000,000, $2,000,000 of which became payable upon the execution of Goldman Sachs' engagement letter with the AMGP Conflicts Committee with respect to the contemplated transaction, and the remainder of which is contingent upon consummation of the Transactions. Goldman Sachs may receive an additional fee of up to $2 million at the AMGP Conflict Committee's sole discretion. In deciding whether and to what extent Goldman Sachs will receive a discretionary fee, it is expected that the AMGP Conflicts Committee will consider, among other factors, the duration of Goldman Sachs' engagement, the services Goldman Sachs provided with respect to the evaluation of a range of strategic alternatives and Goldman Sachs' role in creating a process that the AMGP Conflicts Committee believes led to desirable terms to the Transaction, to the benefit of the Disinterested AMGP Shareholders. In addition, AMGP has agreed to reimburse Goldman Sachs for certain of its expenses, including attorneys' fees and disbursements, and to indemnify Goldman Sachs and related persons against various liabilities, including certain liabilities under the federal securities laws.

Other Presentations by Goldman Sachs

        In addition to the presentation made to the AMGP Conflicts Committee on October 8, 2018, described under "Special Factors—Opinion of the AMGP Conflicts Committee's Financial Advisor," Goldman Sachs also presented or delivered preliminary presentations to the AMGP Conflicts Committee, and in one case, the AMGP Board, on March 1, 2018, March 22, 2018, April 3, 2018, April 7, 2018, April 10, 2018, April 18, 2018, April 20, 2018, April 23, 2018, May 1, 2018, May 3, 2018, May 8, 2018, May 9, 2018, May 11, 2018, May 18, 2018, May 22, 2018, June 1, 2018, June 6, 2018, June 20, 2018, June 29, 2018, July 18, 2018, August 3, 2018, August 11, 2018, August 20, 2018, August 21, 2018, August 23, 2018, August 27, 2018, August 30, 2018, September 6, 2018, September 13, 2018, September 21, 2018, September 24, 2018, October 3, 2018 and October 6, 2018. Copies of these

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written materials will be attached as exhibits to the Schedule 13E-3 to be filed with the SEC in connection with the Transactions.

        None of these other preliminary presentations by Goldman Sachs, alone or together, constitute, or form the basis of, an opinion of Goldman Sachs with respect to the Aggregate Consideration (as defined in the written opinion delivered by Goldman Sachs to the AMGP Conflicts Committee on October 9, 2018). Information contained in these other preliminary presentations is substantially similar to the information provided in Goldman Sachs' presentation made to the AMGP Conflicts Committee on October 8, 2018, described under "Special Factors—Opinion of the AMGP Conflicts Committee's Financial Advisor." A summary of these other preliminary presentations is provided below. The following summary, however, does not purport to be a complete description of these preliminary presentations or of the preliminary financial analyses performed by Goldman Sachs.

•

The March 1, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a situation overview and preliminary illustrative financial analyses.

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The March 22, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, overviews of the midstream oil and gas industry, recent transactions, market perspectives, market context and recent AMGP and Antero Midstream performance and preliminary illustrative financial analyses.

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The April 3, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update, key outstanding diligence items, overviews of the midstream oil and gas industry, recent transactions, evaluation of potential strategic alternatives, market context, potential market reaction, key workstreams, next steps and process tactics and preliminary illustrative analyses.

•

The April 7, 2018 materials presented to the AMGP Board contained, among other information, a status update and preliminary illustrative financial analyses.

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The April 10, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, alternative perspectives on a conversion of the Series B Units.

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The April 10, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update and preliminary illustrative financial analyses.

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The April 18, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units and an overview of market perspectives.

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The April 20, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units.

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The April 20, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, additional preliminary illustrative financial analyses with respect to the Series B Units.

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The April 23, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a summary of historical general partner equity issuances.

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The May 1, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative analyses with respect to the Series B Units.

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The May 3, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, updated preliminary illustrative financial analyses with respect to the Series B Units.

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•

The May 8, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a process timeline, a preliminary summary of the proposed transaction, a preliminary overview of sources and uses and pro forma structure with respect to the proposed transaction, an illustrative summary term sheet with respect to the proposed transaction, overviews of historical market performance, recent transactions and comparison to peers and preliminary financial analyses.

•

The May 9, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units.

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The May 11, 2018 materials delivered to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units.

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The May 18, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a summary of potential structural alternatives, shareholder analyses and potential shareholder reactions.

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The May 22, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, observations on key matters including the governance focus of investors and change of control matters and an overview of recent transactions.

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The June 1, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units.

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The June 6, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a preliminary summary of the proposed transaction, a preliminary overview of sources and uses and pro forma structure with respect to the proposed transaction, an illustrative summary term sheet with respect to the proposed transaction, overviews of historical market performance, recent transactions and comparison to peers and preliminary illustrative financial analyses.

•

The June 6, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a preliminary summary of the proposed transaction, a preliminary overview of sources and uses and pro forma structure with respect to the proposed transaction, an illustrative summary term sheet with respect to the proposed transaction, overviews of historical market performance, recent transactions and comparison to peers and preliminary illustrative financial analyses.

•

The June 20, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to illustrative dividend policies of New AM.

•

The June 29, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units.

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The July 18, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a summary of the AM July 14 Counterproposal and the AR July 14 Counterproposal and preliminary illustrative financial analyses comparing the foregoing to the AMGP Conflicts Committee's most recent proposal, overviews of market context and research analyst assessments.

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The August 3, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a review of the potential impact of available cash including on potential consideration for the proposed transaction and market context.

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The August 11, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update, preliminary illustrative financial analyses, an overview of market performance and potential exhibits for a potential counterproposal to the AM Conflicts Committee.

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•

The August 20, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update, preliminary illustrative financial analyses and points for discussion with the AM Conflicts Committee.

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The August 21, 2018 materials delivered to the AMGP Conflicts Committee contained, among other information, additional preliminary illustrative financial analyses with respect to premia paid with respect to the potential transaction.

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The August 23, 2018 materials delivered to the AMGP Conflicts Committee contained, among other information, additional preliminary illustrative financial analyses with respect to the Series B Units.

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The August 27, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a summary of the components of the proposed transaction and an overview of alternative structures for consideration with respect to the proposed transaction.

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The August 30, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update and a comparison of offers made by the parties.

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The September 6, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update and preliminary illustrative financial analyses.

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The September 13, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a status update and preliminary illustrative financial analyses.

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The September 21, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, a summary of recent developments, status update and preliminary illustrative financial analyses.

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The September 24, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the Series B Units.

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The October 3, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, preliminary illustrative financial analyses with respect to the impact of an updated illustrative dividend policy for New AM provided to the AMGP Conflicts Committee on October 2, 2018.

•

The October 6, 2018 materials presented to the AMGP Conflicts Committee contained, among other information, additional preliminary financial illustrative analyses with respect to the impact of the illustrative dividend policy for New AM and other preliminary illustrative financial analyses.

        The preliminary financial analyses in these preliminary presentations were based on market, economic and other conditions as they existed as of the dates of the respective presentations as well as other information that was available at those times. Accordingly, the results of the financial analyses differed due to changes in those conditions. Among other things, the results of certain analyses changed as AMGP's and Antero Midstream's respective financial results changed as well as projections made by the management of Antero Resources were revised or adjusted. Finally, Goldman Sachs continued to refine various aspects of its financial analyses with respect to AMGP and Antero Midstream over time.

Opinion of the AM Conflicts Committee's Financial Advisor

        The AM Conflicts Committee retained Tudor Pickering to act as its financial advisor with respect to the provision of an opinion to the AM Conflicts Committee as to the fairness, from a financial point of view, to the Disinterested AM Unitholders of the Merger Consideration to be received by such

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Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement. At the request of the AM Conflicts Committee at a meeting of the AM Conflicts Committee held on October 8, 2018, Tudor Pickering rendered its oral opinion to the AM Conflicts Committee that, as of October 8, 2018, based upon and subject to the assumptions, qualifications, limitations and other matters considered relevant by Tudor Pickering in connection with the preparation of its opinion, the Merger Consideration to be received by the Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement was fair, from a financial point of view, to the Disinterested AM Unitholders. Tudor Pickering subsequently confirmed its oral opinion in writing dated October 8, 2018 to the AM Conflicts Committee.

        The opinion speaks only as of the date it was rendered and not as of the date the Merger and the other Transactions will be completed or any other date. The opinion does not reflect changes that may occur or may have occurred after October 8, 2018, which could alter the facts and circumstances on which Tudor Pickering's opinion was based.

Tudor Pickering's opinion was directed to the AM Conflicts Committee (in its capacity as such), and only addressed the fairness, from a financial point of view, as of the date of the opinion, to the Disinterested AM Unitholders of the Merger Consideration to be received by the Disinterested AM Unitholders in the Merger pursuant to the Simplification Agreement. Tudor Pickering's opinion did not address any other term or aspect of the Simplification Agreement or the Transactions. The full text of Tudor Pickering's written opinion, dated October 8, 2018, which describes the assumptions made, procedures followed, matters considered, and qualifications and limitations of the review undertaken by Tudor Pickering in rendering its opinion, is attached as Annex B to this joint proxy statement/prospectus. The summary of Tudor Pickering's opinion set forth in this joint proxy statement/prospectus is qualified in its entirety by reference to the full text of the opinion. AM Unitholders are urged to read Tudor Pickering's opinion carefully and in its entirety. However, neither Tudor Pickering's written opinion nor the summary of its opinion and the related analyses set forth in this joint proxy statement/prospectus are intended to be, and they do not constitute, a recommendation as to how the AM Conflicts Committee or the AM Board, AMP GP or any other person should act or vote with respect to any matter relating to the Merger, the other Transactions or any other matter.

        Tudor Pickering's opinion to the AM Conflicts Committee was among several factors taken into consideration by the AM Conflicts Committee in making its recommendation to the AM Board regarding the Merger and the other Transactions.

        In connection with rendering its opinion and performing its related financial analyses, Tudor Pickering reviewed, among other things:

•

the draft of the Simplification Agreement, dated October 6, 2018, including any exhibits and schedules thereto meaningful to its analysis;

•

certain publicly available financial statements and other business and financial information, including research analyst reports, with respect to Antero Midstream, Antero Resources and AMGP;

•

certain other communications from Antero Midstream, Antero Resources and AMGP to their respective unitholders or shareholders;

•

certain internal financial information and forecasts for each of Antero Midstream, Antero Resources and AMGP prepared by the senior management of AMP GP, Antero Resources and AMGP GP (for purposes of the discussion under this "—Opinion of the AM Conflicts Committee's Financial Advisor," each such set of internal financial information and forecasts, together with the assumptions upon which it was based, a "Forecast" and, collectively, the "Forecasts"); and

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•

such other documents and information as Tudor Pickering deemed appropriate or advisable and which Tudor Pickering discussed with senior management of AMP GP.

        Tudor Pickering also held discussions with members of the senior management of AMP GP and AMGP GP regarding their assessment of the strategic rationale for, and the potential benefits of, the Transactions and the past and current business operations, financial condition and future prospects of their respective entities and of Merger Sub. In addition, Tudor Pickering reviewed the reported price and trading activity for the AM Common Units and the AMGP Common Shares, compared certain financial and stock market information for Antero Midstream and AMGP with similar information for certain other companies the securities of which are publicly traded, reviewed the financial terms of certain recent business combinations in the midstream energy sector specifically and in other industries generally and performed such other studies and analyses, and considered such other factors, as Tudor Pickering considered appropriate.

        For purposes of its opinion, Tudor Pickering assumed and relied upon, without assuming any responsibility for independent verification, the accuracy and completeness of all of the financial, accounting, legal, tax, regulatory and other information provided to, discussed with or reviewed by or for Tudor Pickering, or publicly available. Tudor Pickering's opinion did not address any legal, regulatory, tax or accounting matters, as to which it understood the AM Conflicts Committee, the AM Board, Antero Midstream and AMP GP received such advice as they deemed necessary from qualified professionals. In particular, in preparing its opinion, Tudor Pickering did not take into account, and expressed no view with regards to, any tax consequences of the Transactions to any of the parties to the Simplification Agreement, other potential participants in the Transactions or their respective affiliates. Tudor Pickering also assumed with the AM Conflicts Committee's consent that the Forecasts had been reasonably prepared on a basis reflecting the best currently available estimates and judgments of the senior management of AMP GP and AMGP GP, and that such Forecasts will be realized in the amounts and time periods contemplated thereby. Tudor Pickering expressed no view or opinion with respect to the Forecasts or the assumptions on which they were based, and Tudor Pickering further assumed, among other things, that the executed Simplification Agreement (together with any exhibits and schedules thereto) would not differ in any respect material to its analyses or opinion from the draft version it examined, referenced above, and that the Transactions would be consummated in accordance with the terms set forth in the Simplification Agreement, without any modification, waiver or delay that would be material to its analysis. The Forecasts used by Tudor Pickering in its analysis reflect certain assumptions regarding the oil and gas industry that were and are subject to significant uncertainty and that, if different than assumed, could have a material impact on Tudor Pickering's analysis and its opinion.

        Tudor Pickering was not requested to, and did not, solicit indications of interest from third parties with respect to a potential alternative transaction involving Antero Midstream. In addition, Tudor Pickering did not make an independent evaluation or appraisal of the assets and liabilities (including any contingent, derivative or off-balance-sheet assets and liabilities) of Antero Midstream, AMGP or any of their respective subsidiaries and Tudor Pickering was not furnished with any such evaluation or appraisal.

        The estimates contained in Tudor Pickering's analyses and the results from any particular analysis are not necessarily indicative of future results, which may be significantly more or less favorable than suggested by such analyses. In addition, analyses relating to the value of businesses or assets neither purport to be appraisals nor do they necessarily reflect the prices at which businesses or assets may actually be sold. Accordingly, Tudor Pickering's analyses and estimates are inherently subject to substantial uncertainty.

        In arriving at its opinion, Tudor Pickering did not attribute any particular weight to any particular analysis or factor considered by it, but rather made qualitative judgments as to the significance and

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relevance of each analysis and factor. Several analytical methodologies were employed by Tudor Pickering in its analyses, and no one single method of analysis should be regarded as determinative of the overall conclusion reached by Tudor Pickering. Each analytical technique has inherent strengths and weaknesses, and the nature of the available information may further affect the significance of particular techniques. Accordingly, Tudor Pickering believes that its analyses must be considered as a whole and that selecting portions of its analyses and of the factors considered by it, without considering all analyses and factors in their entirety, could create a misleading or incomplete view of the evaluation process underlying its opinion. The conclusion reached by Tudor Pickering, therefore, is based on the application of Tudor Pickering's experience and judgment to all analyses and factors considered by Tudor Pickering, taken as a whole.

        Tudor Pickering's opinion did not address the underlying business decision of the AM Conflicts Committee, the AM Board, Antero Midstream, AMP GP or any other party to engage in the Transactions, or the relative merits of the Transactions as compared to any other alternative transaction that might have been available to the parties to the Simplification Agreement. Tudor Pickering's opinion addressed only the fairness, from a financial point of view, as of the date thereof, to the Disinterested AM Unitholders of the Merger Consideration to be received by such Disinterested AM Unitholders pursuant to the Simplification Agreement. Tudor Pickering did not express any view on, and its opinion did not address, any other term, aspect or implication of the Simplification Agreement or the Transactions, including, without limitation, the fairness of the Transactions to, or any consideration received in connection therewith by, creditors or other constituencies of the parties to the Simplification Agreement, any of the officers, directors or employees of the parties to the Simplification Agreement, or any class of such persons. In particular, Tudor Pickering did not express any view on, and its opinion did not address, the fairness to the Series B Holders of the New AM Common Stock to be paid or payable to the Series B Holders in the Series B Exchange, the fairness to the AM Public Unitholders (other than the Disinterested AM Unitholders) of the Merger Consideration to be paid or payable to such AM Public Unitholders, or the fairness to Antero Resources or its subsidiaries of the Merger Consideration to be paid or payable to Antero Resources or its subsidiaries in connection with the Transactions, in each case whether relative to the Merger Consideration to be paid or payable to the Disinterested AM Unitholders pursuant to the Simplification Agreement or otherwise. Tudor Pickering did not express any opinion as to the price at which the AM Common Units, the AMGP Common Shares, the New AM Common Stock or the securities of any other party will trade at any time. Tudor Pickering's opinion was necessarily based on economic, monetary, market and other conditions as in effect on, and the information made available to Tudor Pickering as of, the date of its opinion. Tudor Pickering assumed no obligation to update, revise or reaffirm its opinion and expressly disclaimed any responsibility to do so based on circumstances, developments or events occurring of which Tudor Pickering becomes aware after the date of its opinion. Tudor Pickering's advisory services and its opinion were provided for the information and assistance of the AM Conflicts Committee in connection with its consideration of the Transactions, and such opinion does not constitute a recommendation as to how any holder of interests in Antero Midstream, AMGP or any party to the Transactions should vote with respect to the Merger, any of the other Transactions or any other matter. Tudor Pickering's opinion was reviewed and approved by Tudor Pickering's fairness opinion committee.

        The following is a summary of the material financial analyses performed by Tudor Pickering in connection with the preparation of its opinion and reviewed with the AM Conflicts Committee on October 8, 2018. Unless the context indicates otherwise, enterprise values and equity values used in the selected companies analysis described below were calculated using the closing price of the AM Common Units and the equity securities of the selected companies listed below as of October 5, 2018, and transaction values for the selected transactions analysis described below were calculated on an enterprise value basis based on the value of the equity consideration and other public information available at the time of the relevant transaction's announcement. The analyses summarized below

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include information presented in tabular format. In order to fully understand the financial analyses performed, the tables must be considered together with the textual summary of the analyses.

        For purposes of its analyses, Tudor Pickering reviewed a number of financial metrics including:

•

Enterprise Value—generally the value as of a specified date of the relevant company's outstanding equity securities (taking into account its options and other outstanding convertible securities) plus the value as of such date of its net debt (the value of its outstanding indebtedness, preferred stock and capital lease obligations less the amount of cash on its balance sheet). For the calculation of Antero Midstream enterprise value, the value of the equity securities included the value of AM Common Units, the value of AMGP Common Shares and the implied value of the Series B Units based on contractual terms.

•

EBITDA—generally the amount of the relevant company's earnings before interest, taxes, depreciation and amortization for a specified time period.

•

Distributable Cash Flow, or DCF, or Cash Available for Distribution, or CAFD—generally EBITDA minus interest expense and maintenance capital expenditures, as adjusted for special items for a specified time period. For a master limited partnership, or MLP, Distributable Cash Flow is generally the DCF available for distribution to holders of limited partnership units for a specified time period.

•

Distribution Yield—generally the distribution per unit or share divided by the unit or share price.

        No company or transaction used in the analyses of companies or transactions summarized below is identical or directly comparable to Antero Midstream, AMGP or the Transactions. As a consequence, mathematical derivations (such as the high, low, mean and median) of financial data are not by themselves meaningful, and these analyses must take into account differences in the financial and operating characteristics of the selected publicly traded companies and differences in the structure and timing of the selected transactions and other factors that would affect the public trading value and acquisition value of the companies considered.

Forecasts

        The Forecasts each included a base case prepared by senior management of AMP GP, Antero Resources and AMGP GP, as well as a downside case, resulting from adjustments by senior management of AMP GP, Antero Resources and AMGP GP to the applicable base case.

Selected Comparable Company Analysis

        Tudor Pickering reviewed and analyzed certain financial information including valuation multiples for selected companies deemed similar to Antero Midstream or AMGP on a standalone basis, and New AM pro forma for the Transactions, in one or more respects, using estimates of financial performance for the selected companies based on publicly available information and research analyst consensus estimates for the selected companies.

Antero Midstream

        The selected companies for Antero Midstream were: Western Gas Partners, LP, CNX Midstream Partners LP, Hess Midstream Partners LP, Noble Midstream Partners LP, EQT Midstream Partners, LP, Shell Midstream Partners, L.P., BP Midstream Partners LP, Valero Energy Partners LP and Phillips 66 Partners LP (the "AM Peers"). The information reviewed and compared included:

•

estimated distribution yield for the year 2018, or "2018E distribution yield";

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•

unit price as a multiple of estimated distributable cash flow per unit for the years 2019 and 2020, or "2019E DCF/Unit" and "2020E DCF/Unit"; and

•

enterprise value as a multiple of estimated EBITDA for the years 2019 and 2020, or "2019E EBITDA" and "2020E EBITDA."

        The resulting high, low, mean and median data for such companies and the corresponding data for Antero Midstream were:

	Distribution Yield			Price/ DCF/ Unit				Enterprise Value/ EBITDA
	2018E			2019E		2020E		2019E		2020E
Mean		6.6	%		10.8x		9.7x		10.5x		8.7x
Median		6.2	%		11.3x		9.3x		10.6x		8.8x
Low		5.4	%		8.6x		7.3x		8.1x		6.8x
High		8.4	%		13.3x		12.5x		11.8x		10.5x
AM (based on publicly available consensus analyst estimates)		5.7	%		11.0x		9.4x		11.1x		9.0x
AM (based on the Forecasts)		5.8	%		10.9x		9.2x		10.4x		8.4x

AMGP

        The selected companies for AMGP were: EQT GP Holdings, LP and Western Gas Equity Partners, LP (the "AMGP Peers"). The information reviewed and compared included:

•

estimated total entity distribution yield for each general partner of MLPs, or GP, for the year 2018, or "2018E total entity distribution yield";

•

total entity enterprise value of each GP as a multiple of estimated EBITDA (which is calculated (i) for the selected companies, as total distributions to the GP and (ii) for AMGP (pro forma for the exchange of the Series B Units for shares of New AM Common Stock), as total distributions to IDR Holdings) for the years 2019 and 2020, or "2019E GP EBITDA" and "2020E GP EBITDA"; and

•

implied GP equity value (which is calculated as the closing price per unit on October 5, 2018 for each GP multiplied by the number of GP units outstanding) as a multiple of estimated CAFD for the years 2019 and 2020, or "2019E CAFD" and "2020E CAFD."

        The resulting high, low, mean and median data and corresponding data for AMGP were:

	Total Entity Distribution Yield			Total Entity Enterprise Value/ GP EBITDA				Implied GP Equity Value/ CAFD
	2018E			2019E		2020E		2019E		2020E
Mean		6.5	%		14.9x		12.6x		13.2x		11.5x
Median		6.5	%		14.9x		12.6x		13.2x		11.5x
Low		5.7	%		14.9x		12.2x		12.6x		11.1x
High		7.3	%		14.9x		12.9x		13.8x		11.9x
AMGP (based on publicly available consensus analyst estimates)		3.1	%		20.2x		14.7x		20.2x		14.1x
AMGP (based on the Forecasts)		3.1	%		14.9x		9.9x		20.1x		13.3x

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New AM Pro Forma for the Transactions

        The selected companies for New AM pro forma for the Transactions were: Kinder Morgan, Inc., ONEOK, Inc., Plains All American Pipeline, L.P., SemGroup Corporation, Targa Resources Corp., The Williams Companies, Inc., Tallgrass Energy, LP, CNX Midstream Partners LP, EQT Midstream Partners, LP, Hess Midstream Partners LP, Noble Midstream Partners LP, BP Midstream Partners LP, Shell Midstream Partners, L.P. and Valero Energy Partners LP. The information reviewed and compared included:

•

estimated distribution yield for the year 2018, or "2018E distribution yield";

•

equity value as a multiple of estimated distributable cash flow per unit for the years 2019 and 2020, or "2019E DCF/Unit" and "2020E DCF/Unit"; and

•

enterprise value as a multiple of estimated EBITDA for the years 2019 and 2020, or "2019E EBITDA" and "2020E EBITDA."

        The resulting mean and median data and corresponding data for New AM on a pro forma basis were:

	Distribution Yield			Equity Value/ DCF/Unit				Enterprise Value/ EBITDA
	2018E			2019E		2020E		2019E		2020E
Mean		6.1	%		11.6x		10.2x		13.4x		11.1x
Median		5.7	%		11.5x		10.3x		12.9x		10.5x
New AM (pro forma for the Transactions)
Downside		—			13.2x		10.5x		13.1x		10.1x
Base		—			11.6x		9.8x		11.3x		9.1x

Selected Transactions Analysis

        Tudor Pickering reviewed the financial terms of certain transactions since January 1, 2011 by affiliated and third-party MLPs, public GPs and corporations, including transactions where the target company is an MLP, that Tudor Pickering deemed similar to the Transactions in one or more respects. The information reviewed and compared included transaction total enterprise value, or TEV, as a multiple of estimated EBITDA for the next fiscal year "FY1" following announcement, based on publicly available information and research analyst estimates for those targets.

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        The selected transactions and resulting high, low, mean and median data were:

Acquirer	Target
Enbridge Inc.*	Enbridge Energy Partners, L.P.
Enbridge Inc.*	Spectra Energy Partners, LP
Energy Transfer Equity, L.P.*	Energy Transfer Partners, L.P.
Cheniere Energy, Inc.*	Cheniere Energy Partners LP Holdings, LLC
The Williams Companies, Inc.*	Williams Partners L.P.
Tallgrass Energy GP, LP*	Tallgrass Energy Partners, LP
Terra Nitrogen GP Inc.*	Terra Nitrogen Company, L.P.
Archrock, Inc.*	Archrock Partners, L.P.
Zenith Energy U.S., L.P.	Arc Logistics Partners LP
Energy Transfer Partners, L.P.*	PennTex Midstream Partners, LP
VTTI B.V.*	VTTI Energy Partners LP
World Point Terminals, Inc.*	World Point Terminals, LP
ONEOK, Inc.*	ONEOK Partners, L.P.
Enbridge Energy Company, Inc.*	Midcoast Energy Partners, L.P.
Sunoco Logistics Partners L.P.*	Energy Transfer Partners, L.P.
American Midstream Partners, LP	JP Energy Partners LP
TransCanada Corporation*	Columbia Pipeline Partners LP
SemGroup Corporation*	Rose Rock Midstream, L.P.
Targa Resources Corp.*	Targa Resources Partners LP
Transocean Inc.*	Transocean Partners LLC
Western Refining, Inc.	Northern Tier Energy LP
MPLX LP	MarkWest Energy Partners, L.P.
Crestwood Equity Partners LP*	Crestwood Midstream Partners LP
Tesoro Logistics LP*	QEP Midstream Partners, LP
Energy Transfer Partners, L.P.*	Regency Energy Partners LP
Williams Partners L.P.*	Access Midstream Partners LP
Targa Resources Partners LP	Atlas Pipeline Partners LP
Enterprise Products Partners L.P.*	Oiltanking Partners, L.P.
Kinder Morgan, Inc.*	Kinder Morgan Energy Partners, L.P.
Kinder Morgan, Inc.*	El Paso Pipeline Partners, L.P.
Breitburn Energy Partners LP	QR Energy, LP
Regency Energy Partners LP	PVR Partners, L.P.
Plains All American Pipeline, L.P.*	PAA Natural Gas Storage, L.P.
Inergy Midstream, L.P.	Crestwood Midstream Partners LP
Kinder Morgan Energy Partners, L.P.	Copano Energy, L.L.C.
Enterprise Products Partners L.P.*	Duncan Energy Partners L.P.

*

Affiliate Transaction

	Transaction TEV/ FY1 EBITDA
Affiliate Transactions
Median		10.6x
Mean		10.8x
Third-Party Transactions
Median		13.5x
Mean		14.0x
All Transactions
Median		11.2x
Mean		11.6x

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Levered Discounted Cash Flow Analysis

        Tudor Pickering calculated implied value reference ranges of AM Common Units and AMGP Common Shares on a standalone basis by discounting estimated levered distributable cash flow to AM Unitholders and to IDR Holdings, respectively, as of December 31, 2018. Tudor Pickering applied equity discount rates ranging from 8.0% to 12.0% (based on, among other things, Tudor Pickering's judgment of the estimated range of the cost of equity based on an analysis of Antero Midstream and the AM Peers) and terminal value DCF multiples ranging from 9.0x to 12.0x (selected by Tudor Pickering by reference to Price to DCF/Unit trading multiples calculated for the AM Peers) to the estimated 2022 levered distributable cash flow for Antero Midstream based on the Forecasts, which resulted in implied value reference ranges per AM Common Unit of $31.36 to $43.50 based on the downside case and $35.42 to $49.18 based on the base case. Tudor Pickering applied equity discount rates ranging from 8.0% to 12.0% (based on, among other things, Tudor Pickering's judgment of the estimated range of the cost of equity based on an analysis of AMGP and the AMGP Peers) and terminal value CAFD multiples ranging from 12.0x to 16.0x (selected by Tudor Pickering by reference to Implied GP Equity Value to CAFD trading multiples calculated for the AMGP Peers) to the estimated 2022 levered cash available for distribution for AMGP based on the Forecasts and pro forma for the exchange of the Series B Units for shares of New AM Common Stock, which resulted in implied value reference ranges per AMGP Common Share of $17.57 to $24.93 based on the downside case and $22.10 to $31.49 based on the base case.

Discounted Distribution/Dividend Analysis

        Tudor Pickering calculated implied value reference ranges of AM Common Units and AMGP Common Shares on a standalone basis by discounting estimated distributions to AM Unitholders and to AMGP Shareholders, respectively, as of December 31, 2018. Tudor Pickering applied equity discount rates ranging from 8.0% to 12.0% (based on, among other things, Tudor Pickering's judgment of the estimated range of the cost of equity based on an analysis of Antero Midstream and the AM Peers) and terminal distribution yields ranging from 6.0% to 8.0% (selected by Tudor Pickering by reference to Distribution Yields calculated for the AM Peers) to the estimated 2022 distributions for Antero Midstream based on the Forecasts, which resulted in implied value reference ranges per AM Common Unit of $36.87 to $52.06 based on the downside case and $43.55 to $61.73 based on the base case. Tudor Pickering applied equity discount rates ranging from 8.0% to 12.0% (based on, among other things, Tudor Pickering's judgment of the estimated range of the cost of equity based on an analysis of AMGP and the AMGP Peers) and terminal distribution yields ranging from 5.0% to 7.0% (selected by Tudor Pickering by reference to Distribution Yields calculated for the AMGP Peers) to the estimated 2022 distributions for AMGP based on the Forecasts, which resulted in implied value reference ranges per AMGP Common Share of $20.38 to $30.42 based on the downside case and $25.69 to $38.50 based on the base case.

Has/Gets—Discounted Cash Flow and Distribution Analyses

        Tudor Pickering calculated implied value reference ranges of shares of New AM Common Stock pro forma for the Transactions by discounting estimated levered distributable cash flows to New AM Stockholders as of December 31, 2018 based on the Forecasts. Tudor Pickering applied equity discount rates ranging from 8.0% to 12.0% and terminal value DCF multiples ranging from 10.0x to 14.0x to the estimated 2022 levered distributable cash flow for New AM pro forma for the Transactions based on the Forecasts and adjusted the resulting per share value reference ranges by the exchange ratio provided for in the Transactions of 1.6350x plus $3.415 in cash consideration with respect to the Disinterested AM Unitholders. The discounted cash flow analysis for New AM pro forma for the Transactions resulted in implied value reference ranges per share of New AM Common Stock of $38.00 to $53.79 based on the downside case and $43.50 to $61.88 based on the base case, as compared to the

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implied value reference ranges for AM Common Units indicated by the discounted cash flow analysis with respect thereto (using terminal value DCF multiples ranging from 9.0x to 12.0x) of $31.36 to $43.50 based on the downside case and $35.42 to $49.18 based on the base case.

        Tudor Pickering also calculated implied value reference ranges of shares of New AM Common Stock pro forma for the Transactions by discounting estimated distributions to New AM Stockholders as of December 31, 2018 based on the Forecasts. Tudor Pickering applied equity discount rates ranging from 8.0% to 12.0% and terminal distribution yields ranging from 5.0% to 7.0% to the estimated 2022 distributions for AMGP based on the Forecasts and adjusted the resulting per share value reference ranges by the exchange ratio provided for in the Transactions of 1.8326x with respect to the Disinterested AM Unitholders. The distribution analysis for New AM pro forma for the Transactions resulted in adjusted implied value reference ranges per share of New AM Common Stock of $40.80 to $58.87 based on the downside case and $48.34 to $70.30 based on the base case, as compared to the implied value reference ranges for AMGP Common Shares indicated by the distribution analysis with respect thereto (using terminal distribution yields ranging from 6.0% to 8.0%) of $36.87 to $52.06 based on the downside case and $43.55 to $61.73 based on the base case.

        Tudor Pickering also calculated implied value reference ranges of shares of New AM Common Stock pro forma for the Transactions by discounting estimated unlevered free cash flows as of December 31, 2018 based on the Forecasts. Tudor Pickering applied unlevered discount rates ranging from 7.0% to 10.0% and terminal value EBITDA multiples ranging from 11.0x to 15.0x to the estimated 2022 unlevered free cash flows for New AM pro forma for the Transactions based on the Forecasts, deducted net debt to calculate pro forma New AM implied value reference ranges per share and adjusted the resulting per share value reference ranges by a range of estimates of the weighted average cost of capital. The discounted cash flow analysis for New AM pro forma for the Transactions resulted in adjusted implied value reference ranges per share of New AM Common Stock of $40.54 to $58.83 based on the downside case and $45.83 to $67.09 based on the base case.

Present Value of Future Share Price Analysis

        Tudor Pickering performed illustrative analyses of the implied present values of the future values of AM Common Units and AMGP Common Shares, in each case on a standalone basis, and of New AM Common Stock after the Transactions. Tudor Pickering evaluated fiscal years 2019 through 2021 to calculate implied future values per AM Common Unit, AMGP Common Share and share of New AM Common Stock based on the next fiscal year "FY1" annual distributions divided by yield. Tudor Pickering accounted for interim distributions or dividends to respective unitholders or shareholders of Antero Midstream, AMGP and New AM pro forma for the Transactions, as applicable, by discounting such distributions or dividends upon receipt back to December 31, 2018. Tudor Pickering selected a terminal yield value range of 6.0% to 8.0% for Antero Midstream and 5.0% to 7.0% for AMGP and New AM pro forma for the Transactions. Tudor Pickering then discounted the implied future values for fiscal years 2019 through 2021 back to December 31, 2018 using an illustrative discount rate of 10%, reflecting an estimate of the cost of equity for Antero Midstream, AMGP and New AM pro forma for the Transactions. From this analysis, Tudor Pickering estimated a range of implied prices per AM Common Unit of $32.81 to $51.56 based on the downside case and $36.09 to $61.14 based on the base case, compared to the implied prices per AMGP Common Share of $16.29 to $30.14 based on the downside case and $18.92 to $38.15 based on the base case, and to the implied prices per share of New AM Common Stock of $36.59 to $56.04 based on the downside case and $40.35 to $67.08 based on the base case.

Contribution Analysis

        Tudor Pickering reviewed the contributions of Antero Midstream and AMGP of certain financial metrics to New AM pro forma for the Transactions based on the Forecasts and certain publicly

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available financial information for Antero Midstream and AMGP. The financial metrics reviewed, which were based on actual forecasted taxes and included payments to Series B Holders, included (i) distributable cash flow for the year 2017 and estimated distributable cash flow for the years 2018, 2019, 2020, 2021 and 2022 and (ii) distributions for the year 2017 and estimated distributions for the years 2018, 2019, 2020, 2021 and 2022, using the base and downside cases for Antero Resources included in the Forecasts. The contribution analysis indicated a range of implied ownership percentages and implied exchange ratios in the Transactions as set forth in the table below, as compared to the exchange ratio of 1.8326x provided for in the Transactions with respect to the Disinterested AM Unitholders.

	Implied Ownership Percentage
	Antero Midstream			AMGP			Implied Exchange Ratio
Distributable Cash Flow
2017A Distributable Cash Flow		76.0	%		24.0	%	3.175x
Base
2018E Distributable Cash Flow		70.4	%		29.6	%	2.381x
2019E Distributable Cash Flow		66.6	%		33.4	%	1.996x
2020E Distributable Cash Flow		65.8	%		34.2	%	1.926x
2021E Distributable Cash Flow		65.0	%		35.0	%	1.860x
2022E Distributable Cash Flow		64.6	%		35.4	%	1.821x
Levered Discounted Cash Flow(1)		—			—		1.240x - 2.014x
Downside
2018E Distributable Cash Flow		70.5	%		29.5	%	2.386x
2019E Distributable Cash Flow		69.1	%		30.9	%	2.235x
2020E Distributable Cash Flow		66.1	%		33.9	%	1.954x
2021E Distributable Cash Flow		65.7	%		34.3	%	1.913x
2022E Distributable Cash Flow		64.9	%		35.1	%	1.849x
Levered Discounted Cash Flow(1)		—			—		1.386x - 2.241x
Distributions
2017A Distributions		82.9	%		17.1	%	5.334x
Base
2018E Distributions		75.9	%		24.1	%	3.148x
2019E Distributions		71.4	%		28.6	%	2.493x
2020E Distributions		68.2	%		31.8	%	2.146x
2021E Distributions		66.5	%		33.5	%	1.987x
2022E Distributions		65.2	%