Summary of Significant Accounting Policies	9 Months Ended
Sep. 30, 2020
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	(2) Summary of Significant Accounting Policies Basis of Presentation and Consolidation The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United Stated (“US GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (the “SEC”) regarding interim financial reporting, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. These condensed consolidated financial statements include the accounts of C4 Therapeutics, Inc. and its subsidiary C4T Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation. Unaudited Interim Financial Information The accompanying condensed consolidated balance sheet as of September 30, 2020, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2020 and 2019, the condensed consolidated statements of redeemable convertible preferred stock and stockholders’ deficit for the three and nine months ended September 30, 2020 and 2019, the condensed consolidated statements of cash flows for the nine months ended September 30, 2020 and 2019, and the related interim disclosures are unaudited. These unaudited condensed consolidated financial statements include all adjustments necessary, consisting of only normal recurring adjustments, to fairly state the financial position and the results of the Company’s operations and cash flows for interim periods in accordance with U.S. GAAP. Interim period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and unaudited condensed consolidated statements included in the Company’s prospectus related to the Company’s IPO effective on October 1, 2020, pursuant to Rule 424(b) under the Securities Act (the “Prospectus”). Significant Accounting Policies The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2019, which are included in the Prospectus. An update and supplement to these accounting policies follows. Short-Term Investments The Company classifies all short-term investments with an original maturity when purchased of greater than three months as available-for-sale. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in other comprehensive loss. The amortized cost of debt securities in this category is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization is included in interest income. Realized gains and losses and declines in value judged to be other than temporary on available-for-sale securities, are included in interest income. The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. To determine whether an other-than-temporary impairment exists, the Company considers whether it has the ability and intent to hold the investment until a market price recovery, and whether evidence indicating the recoverability of the cost of the investment outweighs evidence to the contrary. The Company’s short-term investments as of September 30, 2020 of $136.0 million consisted entirely of US Treasury securities. Deferred Offering Costs The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings, including the IPO, as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should an in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the condensed consolidated statements of operations and comprehensive loss. The Company had $2.9 million of deferred offering costs related to the IPO as of September 30, 2020. Warrant Liability In connection with the Company’s completion of a financing involving the sale of shares of Series B redeemable convertible preferred stock (the “Series B Financing”) in June and July 2020 and the entry into the Term Loan (see note 8), the Company issued a warrant to purchase shares of its Series B Preferred Stock. The Company classified the warrant as a liability on its consolidated balance sheet. The Company remeasures this warrant liability to fair value at each reporting date and recognizes changes in the fair value of the warrant liability as a component of other income (expense), net in the consolidated statement of operations and comprehensive loss. The Company utilized the Black-Scholes option-pricing model, which incorporates assumptions and estimates, to value these warrants. The Company assesses these assumptions and estimates on a quarterly basis. Estimates and assumptions impacting the fair value measurement include the fair value per share of the underlying redeemable convertible Series B Preferred Stock or common stock issuable upon exercise of the warrant, remaining contractual term of the warrant, risk-free interest rate, expected dividend yield and expected volatility of the price of the underlying redeemable convertible preferred stock or common stock. See Note 13.

Summary of Significant Accounting Policies

9 Months Ended

Sep. 30, 2020

Summary of Significant Accounting Policies

(2) Summary of Significant Accounting Policies

Basis of Presentation and Consolidation

The accompanying interim unaudited condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United Stated (“US GAAP”) and applicable rules and regulations of the Securities and Exchange Commission (the “SEC”) regarding interim financial reporting, and the instructions to Form 10-Q and Article 10 of Regulation S-X. Accordingly, they do not include all of the information and footnotes required by GAAP for complete financial statements. These condensed consolidated financial statements include the accounts of C4 Therapeutics, Inc. and its subsidiary C4T Securities Corporation. All intercompany balances and transactions have been eliminated in consolidation.

Unaudited Interim Financial Information

The accompanying condensed consolidated balance sheet as of September 30, 2020, the condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2020 and 2019, the condensed consolidated statements of redeemable convertible preferred stock and stockholders’ deficit for the three and nine months ended September 30, 2020 and 2019, the condensed consolidated statements of cash flows for the nine months ended September 30, 2020 and 2019, and the related interim disclosures are unaudited. These unaudited condensed consolidated financial statements include all adjustments necessary, consisting of only normal recurring adjustments, to fairly state the financial position and the results of the Company’s operations and cash flows for interim periods in accordance with U.S. GAAP. Interim period results are not necessarily indicative of results of operations or cash flows for a full year or any subsequent interim period. The accompanying condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and unaudited condensed consolidated statements included in the Company’s prospectus related to the Company’s IPO effective on October 1, 2020, pursuant to Rule 424(b) under the Securities Act (the “Prospectus”).

Significant Accounting Policies

The Company’s significant accounting policies are disclosed in the audited consolidated financial statements for the year ended December 31, 2019, which are included in the Prospectus. An update and supplement to these accounting policies follows.

Short-Term Investments

The Company classifies all short-term investments with an original maturity when purchased of greater than three months as available-for-sale. Available-for-sale securities are carried at fair value, with the unrealized gains and losses reported in other comprehensive loss. The amortized cost of debt securities in this category is adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization is included in interest income. Realized gains and losses and declines in value judged to be other than temporary on available-for-sale securities, are included in interest income.

The cost of securities sold is based on the specific identification method. Interest and dividends on securities classified as available-for-sale are included in interest income. To determine whether an other-than-temporary impairment exists, the Company considers whether it has the ability and intent to hold the investment until a market price recovery, and whether evidence indicating the recoverability of the cost of the investment outweighs evidence to the contrary.

The Company’s short-term investments as of September 30, 2020 of $136.0 million consisted entirely of US Treasury securities.

Deferred Offering Costs

The Company capitalizes certain legal, accounting and other third-party fees that are directly associated with in-process equity financings, including the IPO, as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded in stockholders’ (deficit) equity as a reduction of proceeds generated as a result of the offering. Should an in-process equity financing be abandoned, the deferred offering costs will be expensed immediately as a charge to operating expenses in the condensed consolidated statements of operations and comprehensive loss. The Company had $2.9 million of deferred offering costs related to the IPO as of September 30, 2020.

Warrant Liability

In connection with the Company’s completion of a financing involving the sale of shares of Series B redeemable convertible preferred stock (the “Series B Financing”) in June and July 2020 and the entry into the Term Loan (see note 8), the Company issued a warrant to purchase shares of its Series B Preferred Stock. The Company classified the warrant as a liability on its consolidated balance sheet. The Company remeasures this warrant liability to fair value at each reporting date and recognizes changes in the fair value of the warrant liability as a component of other income (expense), net in the consolidated statement of operations and comprehensive loss.

The Company utilized the Black-Scholes option-pricing model, which incorporates assumptions and estimates, to value these warrants. The Company assesses these assumptions and estimates on a quarterly basis. Estimates and assumptions impacting the fair value measurement include the fair value per share of the underlying redeemable convertible Series B Preferred Stock or common stock issuable upon exercise of the warrant, remaining contractual term of the warrant, risk-free interest rate, expected dividend yield and expected volatility of the price of the underlying redeemable convertible preferred stock or common stock. See Note 13.