X0306 4 2021-03-31 0 0001549922 Summit Midstream Partners, LP SMLP 0001823482 Johnston James David C/O SUMMIT MIDSTREAM PARTNERS, LP 910 LOUISIANA STREET, SUITE 4200 HOUSTON TX 77002 0 1 0 0 See remarks below. Common Units 2021-03-31 4 M 0 16667 A 16667 D Common Units 2021-03-31 4 F 0 4058 24.10 D 12609 D Phantom Units 2021-03-31 4 M 0 16667 0.00 D Common Units 16667 16666 D Each phantom unit is the economic equivalent of one common unit. On November 9, 2020, the Issuer effected a 1-for-15 reverse unit split (the "Reverse Unit Split"). Pursuant to the Reverse Unit Split, common unitholders received one common unit for every 15 common units owned at the close of business on November 9, 2020. All fractional units created by the Reverse Unit Split were rounded to the nearest whole unit. The common units began trading on a split-adjusted basis on November 10, 2020. After giving effect to the Reverse Unit Split, the number of issued and outstanding common units decreased to 3,774,992. Common Units being withheld to pay tax liability. One-half of the phantom units (rounded down to the nearest whole number of units, except in the case of the final vesting date) shall vest on March 31, 2021, and the other half shall vest on March 31, 2022, subject to continued employment and accelerated vesting as provided in the applicable award agreement. The Reporting Person will receive Distribution Equivalent Rights ("DERs") for each phantom unit, if applicable, providing for payment on the vesting date of a lump sum of cash equal to any accrued distributions from and after the grant date of the phantom units. The phantom units and associated DERs do not expire. The phantom units are settled upon vesting in common units (on a one-for-one basis) or in cash, at the discretion of the Issuer. Total excludes phantom units from other tranches with different vesting and expiration dates. The Reporting Person is Executive Vice President, General Counsel, and Chief Compliance Officer of Summit Midstream GP, LLC, the general partner of the Issuer (the "General Partner"). The Issuer is managed by the directors and executive officers of the General Partner. /s/ James D. Johnston 2021-04-01