Terns Pharmaceuticals (TERN) 10-Q 15 Nov 21 2021 Q3 Quarterly report Financial data

Document and Entity Information

Document and Entity Information - shares	9 Months Ended
	Sep. 30, 2021	Nov. 05, 2021
Cover [Abstract]
Document Type	10-Q
Amendment Flag	false
Document Period End Date	Sep. 30, 2021
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3
Entity Registrant Name	Terns Pharmaceuticals, Inc.
Entity Central Index Key	0001831363
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity Small Business	true
Entity Common Stock, Shares Outstanding		25,267,271
Entity Current Reporting Status	Yes
Entity Shell Company	false
Entity File Number	001-39926
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	98-1448275
Entity Address Address Line1	1065 East Hillsdale Blvd
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Foster City
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94404
City Area Code	650
Local Phone Number	525-5535
Document Quarterly Report	true
Document Transition Report	false
Entity Interactive Data Current	Yes
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	TERN
Security Exchange Name	NASDAQ

Condensed Consolidated Balance

Condensed Consolidated Balance Sheets - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Current assets:
Cash and cash equivalents	$ 64,751	$ 74,854
Marketable securities	112,445
Notes receivable	0	12,718
Deferred offering costs	0	2,137
Prepaid expenses and other current assets	1,598	1,160
Total current assets	178,794	90,869
Property and equipment, net	927	1,175
Other assets	169	246
Total assets	179,890	92,290
Current liabilities:
Accounts payable	1,582	935
Accrued expenses and other current liabilities	5,311	9,006
Loans payable	0	12,880
Total current liabilities	6,893	22,821
Deferred rent, net of current portion	176	220
Taxes payable, non-current	665	657
Total liabilities	7,734	23,698
Commitments and contingencies
Convertible preferred stock, $0.0001 par value; 10,000,000 and 188,029,084 shares authorized as of September 30, 2021 and December 31, 2020, respectively; no shares issued or outstanding as of September 30, 2021; 12,958,452 shares issued and outstanding as of December 31, 2020	0	186,033
Stockholders’ equity (deficit):
Common stock, $0.0001 par value, 150,000,000 and 299,700,000 shares authorized at September 30, 2021 and December 31, 2020, respectively; 25,264,845 and 337,508 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	3	0
Additional paid-in capital	340,145	14,598
Accumulated other comprehensive loss	(167)	(124)
Accumulated deficit	(167,825)	(131,915)
Total stockholders’ equity (deficit)	172,156	(117,441)
Total liabilities, convertible preferred stock and stockholders equity	$ 179,890	$ 92,290

Condensed Consolidated Balanc_2

Condensed Consolidated Balance Sheets (Parenthetical) - $ / shares	Sep. 30, 2021	Dec. 31, 2020
Statement Of Financial Position [Abstract]
Convertible preferred stock, par value	$ 0.0001	$ 0.0001
Convertible preferred stock,authorized	10,000,000	188,029,084
Convertible preferred stock, shares issued	0	12,958,452
Convertible preferred stock, shares outstanding	0	12,958,452
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, authorized	150,000,000	299,700,000
Common stock, shares issued	25,264,845	337,508
Common stock, shares outstanding	25,264,845	337,508

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations and Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Operating expenses:
Research and development	$ 7,153	$ 5,404	$ 21,849	$ 20,259
General and administrative	4,715	3,333	14,133	7,998
Total operating expenses	11,868	8,737	35,982	28,257
Loss from operations	(11,868)	(8,737)	(35,982)	(28,257)
Other income (expense):
Interest income	49	1	115	53
Change in fair value of loans payable		(2,366)		(2,366)
Other income, (expense), net	4	(387)	30	30
Total other income (expense), net	53	(2,752)	145	(2,283)
Loss before income tax expense	(11,815)	(11,489)	(35,837)	(30,540)
Income tax expense	(20)	(102)	(73)	(102)
Net loss	(11,835)	(11,591)	(35,910)	(30,642)
Net loss attributable to non-controlling interest		(156)		(518)
Net loss attributable to common stockholders	$ (11,835)	$ (11,435)	$ (35,910)	$ (30,124)
Net loss per share attributable to common stockholders, basic and diluted	$ (0.47)	$ (37.82)	$ (1.64)	$ (111.38)
Weighted average common stock outstanding, basic and diluted	25,148,336	302,336	21,842,706	270,463
Other comprehensive loss:
Net loss	$ (11,835)	$ (11,591)	$ (35,910)	$ (30,642)
Unrealized gain (loss) on available-for-sale securities, net of tax	2		(5)
Foreign exchange translation adjustment, net of tax	5	356	(38)	196
Comprehensive loss	(11,828)	(11,235)	(35,953)	(30,446)
Less: Comprehensive loss attributable to non-controlling interest		(128)		(490)
Comprehensive loss attributable to common stockholders	$ (11,828)	$ (11,107)	$ (35,953)	$ (29,956)

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Noncontrolling Interest, Convertible Preferred Stock and Stockholders' Equity (Deficit) - USD ($) $ in Thousands	Total	Noncontrolling Interest	Common Stock	Additional paid-in capital	Accumulated Other Comprehensive (Loss) Income	Accumulated deficit	Series A convertible preferred stock	Series B convertible preferred stock	Series C convertible preferred stock
Balances at Dec. 31, 2019	$ (90,760)			$ 1,208	$ (106)	$ (91,862)
Balance at Beginning of period at Dec. 31, 2019		$ 14,117					$ 21,938	$ 73,029
Balance at Beginning of period (in shares) at Dec. 31, 2019							2,089,285	2,384,195
Balance at Beginning of period (in shares) at Dec. 31, 2019			215,890
Stock-based compensation expense	202			202
Foreign exchange translation adjustment	(176)				(176)
Net loss	(9,001)					(9,001)
Net loss		(205)
Balances at Mar. 31, 2020	(99,735)			1,410	(282)	(100,863)
Balance at End of period at Mar. 31, 2020		13,912					$ 21,938	$ 73,029	$ 0
Balance at end of period (in shares) at Mar. 31, 2020							2,089,285	2,384,195	0
Balance at end of period (in shares) at Mar. 31, 2020			215,890
Balances at Dec. 31, 2019	(90,760)			1,208	(106)	(91,862)
Balance at Beginning of period at Dec. 31, 2019		14,117					$ 21,938	$ 73,029
Balance at Beginning of period (in shares) at Dec. 31, 2019							2,089,285	2,384,195
Balance at Beginning of period (in shares) at Dec. 31, 2019			215,890
Foreign exchange translation adjustment	196
Net loss	(30,124)
Balances at Sep. 30, 2020	(119,815)		$ 0	2,081	90	(121,986)
Balance at End of period at Sep. 30, 2020		13,599					$ 21,938	$ 73,029	$ 0
Balance at end of period (in shares) at Sep. 30, 2020							2,089,285	2,384,195	0
Balance at end of period (in shares) at Sep. 30, 2020			309,156
Balances at Mar. 31, 2020	(99,735)			1,410	(282)	(100,863)
Balance at Beginning of period at Mar. 31, 2020		13,912					$ 21,938	$ 73,029	$ 0
Balance at Beginning of period (in shares) at Mar. 31, 2020							2,089,285	2,384,195	0
Balance at Beginning of period (in shares) at Mar. 31, 2020			215,890
Vesting of restricted stock	23			23
Vesting of restricted stock (in shares)			83,333
Stock-based compensation expense	190			190
Capital Discount On Issuance of Loans Payable	(87)			(87)
Foreign exchange translation adjustment	16				16
Net loss	(9,688)					(9,688)
Net loss		(157)
Balances at Jun. 30, 2020	(109,281)			1,536	(266)	(110,551)
Balance at End of period at Jun. 30, 2020		13,755					$ 21,938	$ 73,029	$ 0
Balance at end of period (in shares) at Jun. 30, 2020							2,089,285	2,384,195	0
Balance at end of period (in shares) at Jun. 30, 2020			299,223
Exercise of stock options	32			32
Exercise of stock options (in shares)			9,933
Stock-based compensation expense	513			513
Foreign exchange translation adjustment	356				356
Net loss	(11,435)					(11,435)
Net loss		(156)
Balances at Sep. 30, 2020	(119,815)		$ 0	2,081	90	(121,986)
Balance at End of period at Sep. 30, 2020		13,599					$ 21,938	$ 73,029	$ 0
Balance at end of period (in shares) at Sep. 30, 2020							2,089,285	2,384,195	0
Balance at end of period (in shares) at Sep. 30, 2020			309,156
Balances at Dec. 31, 2020	(117,441)			14,598	(124)	(131,915)
Balance at Beginning of period at Dec. 31, 2020	$ 186,033	0					$ 30,000	$ 68,995	$ 87,038
Balance at Beginning of period (in shares) at Dec. 31, 2020	12,958,452						2,857,142	2,600,645	7,500,665
Balance at Beginning of period (in shares) at Dec. 31, 2020			337,508
Conversion of preferred stock to common stock upon closing of the initial public offering	$ 186,033		$ 2	186,031
Temporary equity, conversion of convertible preferred stock into common stock upon closing of the initial public offering (in shares)							(2,857,142)	(2,600,645)	(7,500,665)
Temporary equity, conversion of convertible preferred stock into common stock upon closing of the initial public offering							$ (30,000)	$ (68,995)	$ (87,038)
Conversion of preferred stock to common stock upon closing of the initial public offering (in shares)			16,079,230
Sale of common stock in initial public offering, net of issuance costs	133,023		$ 1	133,022
Sale of common stock in initial public offering, net of issuance costs (in shares)			8,625,000
Stock-based compensation expense	1,832			1,832
Unrealized loss on available-for-sale securities	(43)				(43)
Foreign exchange translation adjustment	(65)				(65)
Net loss	(13,337)					(13,337)
Balances at Mar. 31, 2021	190,002		$ 3	335,483	(232)	(145,252)
Balance at End of period at Mar. 31, 2021		0					$ 0	$ 0	$ 0
Balance at end of period (in shares) at Mar. 31, 2021							0	0	0
Balance at end of period (in shares) at Mar. 31, 2021			25,041,738
Balances at Dec. 31, 2020	(117,441)			14,598	(124)	(131,915)
Balance at Beginning of period at Dec. 31, 2020	$ 186,033	0					$ 30,000	$ 68,995	$ 87,038
Balance at Beginning of period (in shares) at Dec. 31, 2020	12,958,452						2,857,142	2,600,645	7,500,665
Balance at Beginning of period (in shares) at Dec. 31, 2020			337,508
Foreign exchange translation adjustment	$ (38)
Net loss	(35,910)
Balances at Sep. 30, 2021	172,156		$ 3	340,145	(167)	(167,825)
Balance at End of period at Sep. 30, 2021	$ 0	0					$ 0	$ 0	$ 0
Balance at end of period (in shares) at Sep. 30, 2021	0						0	0	0
Balance at end of period (in shares) at Sep. 30, 2021			25,264,845
Balances at Mar. 31, 2021	$ 190,002		$ 3	335,483	(232)	(145,252)
Balance at Beginning of period at Mar. 31, 2021		0					$ 0	$ 0	$ 0
Balance at Beginning of period (in shares) at Mar. 31, 2021							0	0	0
Balance at Beginning of period (in shares) at Mar. 31, 2021			25,041,738
Exercise of stock options	101			101
Exercise of stock options (in shares)			17,446
Vesting of restricted stock (in shares)			71,429
Stock-based compensation expense	1,909			1,909
Unrealized loss on available-for-sale securities	36				36
Foreign exchange translation adjustment	22				22
Net loss	(10,738)					(10,738)
Balances at Jun. 30, 2021	181,332		$ 3	337,493	(174)	(155,990)
Balance at End of period at Jun. 30, 2021		0					$ 0	$ 0	$ 0
Balance at end of period (in shares) at Jun. 30, 2021							0	0	0
Balance at end of period (in shares) at Jun. 30, 2021			25,130,613
Exercise of stock options	797			797
Exercise of stock options (in shares)			134,232
Stock-based compensation expense	1,855			1,855
Unrealized loss on available-for-sale securities	2				2
Foreign exchange translation adjustment	5				5
Net loss	(11,835)					(11,835)
Balances at Sep. 30, 2021	172,156		$ 3	$ 340,145	$ (167)	$ (167,825)
Balance at End of period at Sep. 30, 2021	$ 0	$ 0					$ 0	$ 0	$ 0
Balance at end of period (in shares) at Sep. 30, 2021	0						0	0	0
Balance at end of period (in shares) at Sep. 30, 2021			25,264,845

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Noncontrolling Interest, Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) $ in Thousands	3 Months Ended
	Mar. 31, 2021USD ($)
Statement Of Stockholders Equity [Abstract]
Stock issuance cost	$ 3,339

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Cash Flows - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (35,910)	$ (30,642)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	5,596	905
Depreciation and amortization expense	398	288
Amortization on marketable securities, net	685	37
Change in fair value of convertible notes	0	2,366
Change in deferred taxes and uncertain tax positions	45	0
Changes in operating assets and liabilities:
Prepaid expenses and other current assets	(391)	966
Other assets	(7)	0
Accounts payable	1,221	(1,176)
Accrued expenses and other current liabilities	(2,751)	4,857
Deferred rent	(44)	(23)
Net cash used in operating activities	(31,158)	(22,422)
Cash flows from investing activities:
Purchase of property and equipment	(140)	(537)
Purchase of investments	(146,576)	(715)
Proceeds from sales and maturities of investments	33,441	7,992
Net cash (used in) provided by investing activities	(113,275)	6,740
Cash flows from financing activities:
Net proceeds from initial public offering	136,362	0
Proceeds from notes receivable	12,718	0
Payment of loans payable	(12,880)	0
Payment of deferred offering costs	(2,721)	(33)
Proceeds from stock option exercises	898	32
Proceeds from issuance of loans payable	0	16,876
Net cash provided by financing activities	134,377	16,875
Effect of exchange rate changes on cash, cash equivalents and restricted cash	(47)	236
Net (decrease) increase in cash, cash equivalents and restricted cash	(10,103)	1,429
Cash, cash equivalents and restricted cash at beginning of period	74,854	12,375
Cash, cash equivalents and restricted cash at end of period	64,751	13,804
Supplemental disclosure of noncash investing and financing activities:
Conversion of preferred stock to common stock upon closing of the initial public offering	$ 186,033	$ 0

Organization, Basis of Presenta

Organization, Basis of Presentation and Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Organization, Basis of Presentation and Summary of Significant Accounting Policies	1. Organization, Basis of Presentation and Summary of Significant Accounting Policies Terns Pharmaceuticals, Inc. (Terns) is a clinical-stage biopharmaceutical company developing a portfolio of small-molecule single-agent and combination therapy candidates to address serious diseases such as non-alcoholic steatohepatitis (NASH). Terns was incorporated as an exempted company in the Cayman Islands in December 2016. In December 2020, the Company effected a de-registration of the Company in the Cayman Islands and a domestication in the State of Delaware (the "Domestication"), pursuant to which it became a Delaware corporation. Terns owns all of the share capital of Terns Pharmaceutical HongKong Limited (Terns Hong Kong) and Terns, Inc., a Delaware corporation (Terns U.S. Opco). Terns Hong Kong holds all of the share capital of Terns China Biotechnology Co., Ltd. (organized in Shanghai, People’s Republic of China (PRC)) (Terns China) and Terns (Suzhou) Biotechnology Co., Ltd. (organized in Suzhou, PRC) (Terns Suzhou). Basis of Presentation The accompanying condensed consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) and include the accounts of Terns and its wholly owned subsidiaries Terns U.S. Opco and Terns Hong Kong and its wholly owned subsidiaries Terns China and Terns Suzhou. Prior period reflects a variable interest in Terns China in which Terns had a majority interest and was the primary beneficiary. The noncontrolling interest attributable to the Company’s variable interest entity (VIE) is presented as a separate component from stockholders’ equity (deficit) in the condensed consolidated balance sheets, and a noncontrolling interest in the condensed consolidated statements of operations and comprehensive loss and condensed consolidated statements of noncontrolling interest, convertible preferred stock and stockholders’ equity (deficit). The Company’s condensed consolidated financial statements have been prepared in conformity with U.S. GAAP. All intercompany balances and transactions have been eliminated in consolidation. Initial Public Offering In February 2021, the Company completed an initial public offering (the “IPO”) of 8,625,000 shares of its common stock, including the exercise in full by the underwriters of their option to purchase up to 1,125,000 additional shares of common stock, for net proceeds of $ 133.0 million, after deducting underwriting discounts and commissions and offering expenses, and its shares started trading on the Nasdaq Global Select Market under the ticker symbol “TERN.” Upon closing of the IPO, all of the Company's outstanding shares of convertible preferred stock automatically converted into an aggregate of 16,079,230 shares of common stock. Certificate of Incorporation Prior to the IPO, the Company’s certificate of incorporation adopted in December 2020 in connection with the Domestication (the “December 2020 Charter”) authorized the Company to issue the following shares of capital stock: (i) 299,700,000 shares of common stock, (ii) 40,000,000 shares of Series A convertible preferred stock, (iii) 36,409,088 shares of Series B convertible preferred stock, and (iii) 111,619,996 shares of Series C convertible preferred stock. All classes of stock under the December 2020 Charter were authorized at a par value of $ 0.0001 . In February 2021, the Company’s amended and restated certificate of incorporation filed with the Secretary of State of the State of Delaware became effective in connection with the closing of the IPO. Under the amended and restated certificate of incorporation, the Company is authorized to issue 150,000,000 shares of common stock and 10,000,000 shares of preferred stock. All classes of stock have a par value of $ 0.0001 . Reverse Stock Split In January 2021, the Company filed an amended and restated certificate of incorporation to effectuate a reverse split of shares of the Company’s common stock and convertible preferred stock on a 1 -for-14 basis (the “Reverse Stock Split”). The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock, options to purchase common stock and per share amounts contained in the condensed consolidated financial statements have been retroactively adjusted to give effect to the Reverse Stock Split for all periods presented. Variable Interest Entity The Company consolidates a VIE where it has been determined that the Company is the primary beneficiary of the entity’s operations. The Company has considered its relationships with a certain entity to determine whether the Company has a variable interest in that entity, and if so, whether the Company is the primary beneficiary of the relationship. U.S. GAAP requires VIEs to be consolidated if an entity’s interest in the VIE is a controlling financial interest. Under the variable interest model, a controlling financial interest is determined based on which entity, if any, has (i) the power to direct the activities of the VIE that most significantly impacts the VIE’s economic performance and (ii) the obligations to absorb losses that could potentially be significant to the VIE or the right to receive benefits from the VIE that could potentially be significant to the VIE. Management performs ongoing reassessments of whether changes in the facts and circumstances regarding the Company’s involvement with a VIE will cause the consolidation conclusion to change. The consolidation status of a VIE may change as a result of such reassessments. Changes in consolidation status are applied prospectively in accordance with U.S. GAAP. Impact of the COVID-19 Pandemic The COVID-19 pandemic is rapidly evolving. The COVID-19 virus and new variants that emerge continue to impact countries worldwide, including the United States and China where the Company has business operations. The extent of the impact of the COVID-19 pandemic on business, operations and development timelines and plans remains uncertain, and will depend on certain developments, including the duration and spread of the outbreak and its impact on the Company’s development activities, planned clinical trial enrollment, future trial sites, contract research organizations (CROs), third-party manufacturers and other third parties with whom the Company conducts business, as well as its impact on regulatory authorities and the Company’s key scientific and management personnel. The ultimate impact of the COVID-19 pandemic or a similar health epidemic is highly uncertain and subject to change. To the extent possible, the Company is conducting business as usual, with necessary or advisable modifications to employee travel and to the on-site and in-person activities of the Company's personnel. The Company will continue to actively monitor the rapidly evolving situation related to the COVID-19 pandemic and may take further actions that alter the Company’s operations, including those that may be required by federal, state or local authorities in the United States and China, or that the Company determines are in the best interest of its employees and other third parties with whom the Company conducts business. At this point, the extent to which the COVID-19 pandemic may affect the Company’s business, operations and development timelines and plans, including the resulting impact on expenditures and capital needs, remains uncertain. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to, the estimates for accruals of research and development expenses, accrual of research contract costs, unrecognized tax benefits, fair value of common stock and stock option valuations. On an ongoing basis, the Company evaluates its estimates and judgments, using historical and anticipated results and trends and on various other assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates. Unaudited Interim Financial Information The accompanying unaudited condensed consolidated balance sheet as of September 30, 2021, the unaudited condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020, the unaudited condensed consolidated statements of noncontrolling interest, convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2021 and 2020, the unaudited condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020, and the related 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 unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto in the Company’s Annual Report on Form 10-K (“Annual Report”) for the fiscal year ended December 31, 2020, as filed with the SEC on March 30, 2021. There have been no significant changes to the Company's significant accounting policies described in Note 1, Organization, Basis of Presentation and Summary of Significant Accounting Policies, in Notes to Consolidated Financial Statements in Item 8 of Part II of the Form 10-K for the fiscal year ended December 31, 2020. Cash, Cash Equivalents, Restricted Cash and Marketable Securities Cash and cash equivalents consist of standard checking accounts and money market funds. The Company considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. Restricted cash represents a security deposit related to a lease. The Company classifies as available-for-sale marketable securities with a remaining maturity when purchased of greater than three months. The Company’s marketable securities are maintained by investment managers and consist of government securities, corporate debt securities, asset-backed securities and commercial paper. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity (deficit) until realized. Any premium arising at purchase is amortized to the earliest call date and any discount arising at purchase is accreted to maturity. Amortization and accretion of premiums and discounts are recorded in interest income and/or expense. Realized gains and losses on debt securities are determined using the specific identification method and are included in other income (expense), net. If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, marks the investment to market through a charge to the Company’s condensed consolidated statements of operations and comprehensive loss. The fair value and amortized cost of marketable securities by major security type as of September 30, 2021 is as follows: September 30, 2021 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Money market funds $ 39,213 $ — $ — $ 39,213 U.S. government securities 21,123 5 ( 8 ) 21,120 Non-U.S. government securities 11,203 — ( 1 ) 11,202 Corporate debt securities 44,161 10 ( 11 ) 44,160 Commercial paper 35,963 — — 35,963 Total $ 151,663 $ 15 $ ( 20 ) $ 151,658 Classified as: Cash equivalents $ 39,213 Marketable securities 112,445 Total $ 151,658 The Company did no t have any marketable securities for the year ended December 31, 2020. The reconciliation of cash, cash equivalents and restricted cash reported within the applicable balance sheet line items that sum to the total of the same such amount shown in the consolidated statements of cash flows is as follows: September 30, (in thousands) 2021 2020 Cash and cash equivalents $ 64,751 $ 13,756 Restricted cash, non-current — 48 Total cash, cash equivalents and restricted cash $ 64,751 $ 13,804 Classification of Convertible Preferred Stock and Presentation of Noncontrolling Interest The holders of Series A, Series B and Series C convertible preferred stock, which were outstanding prior to the IPO, had certain liquidation rights in the event of a deemed liquidation that, in certain situations, were not solely within the control of the Company and would call for the redemption of the then outstanding convertible preferred stock. Therefore, the Series A, Series B and Series C convertible preferred stock were classified outside of shareholders’ equity (deficit) on the condensed consolidated balance sheets as of December 31, 2020. In February 2021, upon the completion of the IPO, all the outstanding shares of convertible preferred stock converted into common stock and the Company does not have any shares of preferred stock outstanding. The Company recognizes a noncontrolling interest related to VIEs in which the Company is the primary beneficiary as equity in the condensed consolidated financial statements separate from the parent entity’s equity. The net loss attributable to noncontrolling interest is included in net loss in the condensed consolidated statements of operations and comprehensive loss. Changes in the parent entity’s ownership interest in a subsidiary that do not result in deconsolidation are treated as equity transactions if the parent entity retains its controlling financial interest. In addition, when a subsidiary is deconsolidated, any retained noncontrolling equity investment in the former subsidiary will be initially measured at fair value and the difference between the carrying value and fair value of the retained interest will be recorded as a gain or loss. Terns China, the Company’s VIE, was established as a financing subsidiary to allow investment by Lilly Asia Ventures (LAV) investment entities: Suzhou Litai Equity Investment Centre (Limited Partnership) (PRC) and Suzhou Lirui Equity Investment Centre (Limited Partnership) (PRC), collectively referred to as the “LAV PRC Entities”. The Company’s board of directors has the unilateral ability to control the Terns China board of directors. Net losses of the China Subsidiaries have been allocated based on their ownership percentage to the LAV PRC Entities’ noncontrolling interest and are reflected in the condensed consolidated statements of operations and comprehensive loss. The noncontrolling interest is classified outside of stockholders’ equity (deficit) on the condensed consolidated balance sheets as it is redeemable for cash based on an investor option after a specified date. In December 2020, the LAV PRC Entities exercised their option resulting in the conversion of all of the equity interests in Terns China held by the LAV PRC Entities into shares of the Company’s preferred stock (the “China Conversion”). Following the completion of the China Conversion, Terns China became a wholly owned subsidiary of the Company. The Company does not currently anticipate any further direct third-party investments into Terns China and Terns China will only act as an operating subsidiary for the Company’s business activities in China. Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, allocated facility-related and depreciation expenses, third-party license fees and external costs, including fees paid to consultants and contract research organizations, or CROs, in connection with nonclinical studies and clinical trials and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses. The Company has from time to time entered into various research and development and other agreements with commercial firms, researchers, universities and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company’s estimates. Since inception, the Company’s historical accrual estimates have not been materially different from the actual costs. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities included the following: (in thousands) September 30, 2021 December 31, 2020 Research and development costs $ 1,907 $ 2,800 Refundable contract liability 836 836 Compensation and benefit costs 1,393 1,492 Accrued professional fees 1,092 2,185 Accrued development milestone — 1,531 Other 83 162 Total accrued expenses and other current liabilities $ 5,311 $ 9,006 Income Taxes The provision for income taxes primarily relates to projected federal, state, and foreign income taxes. To determine the quarterly provision for income taxes, the Company uses an estimated annual effective tax rate, which is generally based on expected annual income and statutory tax rates in the various jurisdictions in which the Company operates. In addition, the tax effects of certain significant or unusual items are recognized discretely in the quarter during which they occur and can be a source of variability in the effective tax rates from quarter to quarter. Income taxes are computed using the asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s financial statements. In estimating future tax consequences, the Company considers all expected future events including the enactment of changes in tax laws or rates. A valuation allowance is recorded, if necessary, to reduce net deferred tax assets to their realizable values if management does not believe it is more likely than not that the net deferred tax assets will be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, and ongoing prudent and feasible tax planning strategies in assessing the amount of the valuation allowance. When the Company establishes or reduces the valuation allowance against its deferred tax assets, its provision for income taxes will increase or decrease, respectively, in the period such determination is made. The Company assesses accounting for uncertainty in income taxes by modeling for the recognition, measurement and disclosure in financial statements any uncertain income tax positions that the Company has taken or expects to take on a tax return. As of each balance sheet date, unresolved uncertain tax positions are reassessed. The Company accrues interest and related penalties, if applicable, on all tax exposures for which reserves have been established consistent with jurisdictional tax laws. Common Stock Valuation Due to the absence of an active market for the Company’s common stock prior to the completion of the IPO in February 2021, the Company utilized methodologies to estimate the fair value of its common stock. In determining the fair value of options granted prior to the IPO, the Company has considered the estimated fair value of the common stock as of the measurement date. The estimated fair value of the common stock prior to the IPO was determined at each grant date based upon a variety of factors, including:  the prices at which the Company sold shares of convertible preferred stock and the superior rights and preferences of the convertible preferred stock relative to its common stock at the time of each grant;  the progress of the Company’s research and development programs, including the status and results of clinical and nonclinical studies for its drugs;  the Company’s stage of development and commercialization and its business strategy;  external market conditions affecting the biotechnology industry and trends within the biotechnology industry;  the Company’s financial position, including cash on hand, and its historical and forecasted performance and operating results;  the lack of an active public market for the Company’s common stock and convertible preferred stock;  the likelihood of achieving a liquidity event, such as an IPO or sale of the Company in light of prevailing market conditions; and  the analysis of IPOs and the market performance of similar companies in the biotechnology industry. Significant changes to the key assumptions underlying the factors used could have resulted in different fair values of common stock at each valuation date. Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources. Stock-Based Compensation Stock-based compensation expense, including grants of stock options and restricted stock awards issued under the Company’s equity incentive plan, is measured at the grant date based on the fair value of the awards and is recognized as an expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Company’s determination of the fair value of stock options with time-based vesting utilizes the Black-Scholes option-pricing model. The Company lacks sufficient company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The Company estimates risk-free rates using the implied yield currently available on U.S. Treasury zero-coupon issues with a remaining term equal to the expected term and dividend yield using the Company’s expectations and historical data. The Company uses the simplified method to calculate the expected term of stock option grants. Under the simplified method, the expected term is estimated to be the mid-point between the vesting date and the contractual term of the option. The fair value of each stock option grant is calculated based upon the Company’s common stock valuation on the date of the grant. The Company accounts for forfeitures of stock option grants as they occur. Net Loss Per Share of Common Stock The Company follows the two-class method when computing net income (loss) per share of common stock as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share of common stock for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share of common stock is computed by dividing the net income (loss) per share of common stock by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) per share of common stock is computed by adjusting net income (loss) to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share of common stock is computed by dividing the diluted net loss by the weighted average number of shares of common stock outstanding for the period, including potential dilutive shares. For purposes of this calculation, outstanding stock options and convertible preferred stock are considered potential dilutive shares. The Company’s convertible preferred stock outstanding prior to the IPO contractually entitled the holders of such shares to participate in dividends but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such securities. In periods in which the Company reports a net loss, diluted net loss per share of common stock is the same as basic net loss per share of common stock, since dilutive shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss for the three and nine months ended September 30, 2021 and 2020 . Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction to the carrying value of stockholders’ equity (deficit) as a reduction of additional paid-in capital or equity generated as a result of such 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. Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies. The Company is an emerging growth company as defined in the Jumpstart Our Business Startups Act of 2012, as amended (JOBS Act). Under the JOBS Act, emerging growth companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected to use this exemption to delay adopting new or revised accounting standards until such time as those standards apply to private companies. Where allowable, the Company has early adopted certain standards as described below. Recently Adopted Accounting Pronouncements In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Non-employee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 primarily expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from non-employees. ASU 2018-07 is effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. The Company adopted ASU 2018-07 on January 1, 2021 , and the adoption of this standard did not have an impact on the Company’s consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (ASU 2016-02), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases today. For non-public entities, ASU 2016-02 is effective for annual reporting periods, and interim periods within those fiscal years, beginning after December 15, 2021, and early adoption is permitted. Under the JOBS Act, emerging growth companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected to use this exemption to delay adopting ASU 2016-02. The Company is in the process of completing its review of its existing lease agreements under Topic 842 and does not expect the adoption of ASU 2016-02 to have a material impact on its financial position, results of operations or cash flows. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss methodology, which will result in more timely recognition of credit losses. For non-public entities, ASU 2016-13 is effective for annual reporting periods, and interim periods within those fiscal years, beginning after December 15, 2022. Under the JOBS Act, emerging growth companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected to use this exemption to delay adopting ASU 2016-13. The Company is currently in the process of evaluating the impact of the adoption of ASU 2016-13 on its consolidated financial statements.

Fair Value

Fair Value	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value	2. Fair Value Fair value is defined as the price that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. The three levels of inputs that may be used to measure fair value are defined below:  Level 1—Quoted prices in active markets for identical assets or liabilities at the measurement date.  Level 2—Inputs other than quoted prices included in Level 1 that are observable for the asset or liability, such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities.  Level 3—Unobservable inputs that are supported by little or no market activity that are significant to determining the fair value of the assets or liabilities, including pricing models, discounted cash flow methodologies and similar techniques. The carrying values of the Company’s other assets, accounts payable and accrued expenses and other current liabilities approximate their fair values due to the short-term nature of these assets and liabilities. The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis: Fair Value at September 30, 2021 (in thousands) Level 1 Level 2 Level 3 Total Cash and cash equivalents Cash in bank balances $ 25,538 $ — $ — $ 25,538 Money market funds 39,213 — — 39,213 Total cash and cash equivalents $ 64,751 $ — $ — $ 64,751 Marketable securities U.S. government securities $ — $ 21,120 $ — $ 21,120 Non-U.S. government securities — 11,202 — 11,202 Corporate debt securities — 44,160 — 44,160 Commercial paper — 35,963 — 35,963 Total marketable securities $ — $ 112,445 $ — $ 112,445 Fair Value at December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Total Assets: Cash and cash equivalents $ 74,854 $ — $ — $ 74,854 Total $ 74,854 $ — $ — $ 74,854 Liabilities: Loans payable $ — $ — $ 12,880 $ 12,880 Total $ — $ — $ 12,880 $ 12,880 The aggregate fair value of marketable securities as of September 30, 2021, by contractual maturity, are as follows: (in thousands) Fair Value Due in one year or less $ 77,555 Due after one year through two years 34,890 Total marketable securities $ 112,445 During the nine months ended September 30, 2021 , there were no transfers between Level 1, Level 2 and Level 3.

Loans Payable

Loans Payable	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Loans Payable	3. Loans Payable The following table provides the loans payable reported at fair value and measured on a recurring basis: (in thousands) Loans Payable Balance at December 31, 2019 $ — Issuance of 2020 Notes and Bridge Loan 16,800 Issuance of repurchase payable for the Lilly Asia Ventures option exercise 10,771 Issuance of loans payable for conversion settlement of the Bridge Loan 2,109 Conversion of 2020 convertible promissory notes to Series C convertible preferred stock ( 17,690 ) Conversion of Bridge Loan to Series C convertible preferred stock ( 2,163 ) Change in fair value of loans payable and other adjustments 3,053 Balance at December 31, 2020 $ 12,880 As of September 30, 2021 , there was no loans payable balance. 2020 Notes In May 2020, the Company issued convertible promissory notes (2020 Notes) in the aggregate amount of $ 15.0 million. The 2020 Notes had an interest rate of 10.0 % per annum, were unsecured, and were due and payable, including accrued interest, in May 2021. In connection with the Series C Convertible Preferred Stock Financing, the 2020 Notes, totaling unpaid principal and accrued interest of $ 15.9 million, converted into 1,366,820 shares of Series C convertible preferred stock. Bridge Loan In May 2020, the Company entered into a bridge loan with Terns China (Bridge Loan) for aggregate proceeds of $ 1.8 million, payable in renminbi (RMB) at an established USD/RMB exchange rate, based on an average of the previous five working days before May 8, 2020. The Bridge Loan had an interest rate of 10 % per year, which began to accrue on the date of drawdown, and was computed based on the actual number of days elapsed based on a year of 365 days. The Bridge Loan holders have the same conversion rights as the 2020 Notes holders. In connection with the closing of the Series C convertible preferred stock financing in December 2020, entities that are a part of LAV agreed to effectively convert the Bridge Loan into shares of Series C preferred stock on the same terms as the 2020 Notes. The conversion will be based on an outstanding loan balance equal to $ 1.9 million, consisting of (i) the principal loan amount ($ 1.8 million) plus (ii) accrued interest through December 29, 2020 ($ 0.1 million). To help facilitate the transfer of cash from China to the United States to effectively convert the Bridge Loan, the Company and Terns China agreed to enter into an agreement with LAV to (i) repay the Bridge Loan, and (ii) issue shares of Series C convertible preferred stock at the initial closing of the Series C financing to entities that are a part of LAV in exchange for a promissory note issued to the Company by LAV, or the LAV Affiliate Promissory Note. The Bridge Loan was repaid in full by the Company following the requisite government approvals in China. Proceeds from the repayment of the Bridge Loan by Terns China were used by LAV to repay the LAV Affiliate Promissory Note in full. The fair value of the Bridge Loan was determined to be $ 2.1 million as of December 31, 2020. The Bridge Loan and the LAV Affiliate Promissory Note were paid in full in March 2021. LAV Series A and Series B Promissory Notes In November 2020, the Chinese government provided approval for entities affiliated with LAV to exercise the LAV Option (see Note 4, Convertible Preferred Stock). Terns Hong Kong agreed to repurchase all equity interests held by the LAV PRC Entities with proceeds to be used by LAV to purchase shares of Series A convertible preferred stock and Series B convertible preferred stock of the Company (Repurchase). In December 2020, the Company issued 767,857 shares of Series A convertible preferred stock and 216,450 shares of Series B convertible preferred stock to an affiliate of LAV (LAV Affiliate) in exchange for a promissory note with a principal amount equal to the original investment by LAV in Terns China (LAV Series A and Series B Promissory Note). The LAV Series A and Series B Promissory Note was repaid through proceeds of the Repurchase which was completed in January 2021. The carrying value of the LAV Series A and Series B Promissory Notes approximate its fair value due to the short-term nature of the liability. Change in Fair Value of Loans Payable The fair value of the loans payable liability was determined based on significant inputs not observable in the market, which represents a Level 3 measurement within the fair value hierarchy. The fair value of the loans payable liability is remeasured at each reporting period, with changes in fair value recognized in the condensed consolidated statements of operations. During 2020, the Company used the PWERM method to value the loans payable. This approach involved the estimation of future potential outcomes for the Company, as well as values and probabilities associated with each respective potential outcome. The Company considered two scenarios (i) a 60 % probability of an IPO in the near-term and (ii) a 40 % probability of the Company remaining private for 1.75 years following the date of the valuation. The Company considered these two scenarios to calculate the (i) future value of the loans payable under each scenario and (ii) the present value of the loans payable under each scenario. The value of the Company’s equity used to determine the appropriate allocation of value to the stockholders was calculated using different methodologies for each scenario. For the first scenario, the value of the Company’s equity was estimated based on the Company’s estimates, as well as recent IPO indications of comparable companies. For the second scenario, the value of the Company’s equity was estimated using the income approach, which focuses on the income-producing capability of a business and estimates value based on the expectation of future cash flows, which are then discounted to the present using a rate of return that incorporates the risk-free rate for the use of funds, the expected rate of inflation, and risks associated with the particular investment. Under each scenario, the rights and preferences of each share class were considered in order to determine the appropriate allocation of value to the common and preferred stockholders, as well as the loans payable. The value per share of common and preferred stock, as well as the loans payable, under each scenario was multiplied by a present value factor, calculated based on the Company’s cost of equity and the expected timing of each scenario. After taking into consideration the PWERM of each scenario, the Company arrived at the fair value of the loans payable. The Company recorded other expense of $ 2.9 million related to the change in the fair value of loans payable for the year ended December 31, 2020. The outstanding LAV Series A and Series B Promissory Note was settled in January 2021 and was paid with the proceeds received from the note receivable of $ 10.8 million. The outstanding Bridge Loan was settled in March 2021 and was substantially paid with the proceeds received from the LAV Affiliate Promissory Note receivable of $ 1.9 million.

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2021
Convertible Preferred Stock [Abstract]
Convertible Preferred Stock	4. Convertible Preferred Stock All shares of preferred stock described below were converted into an aggregate of 16,079,230 shares of the Company’s common stock at the time of the IPO in February 2021. Series A Preferred Stock In April 2017, the Company entered into a Series A convertible preferred stock purchase agreement (Series A Agreement) whereby the Company issued 2,089,285 shares of Series A convertible preferred stock at $ 10.50 per share for an aggregate purchase price of $ 21.9 million. Terns China received an aggregate $ 8.0 million from the LAV PRC Entities in connection with the Series A financing, which is presented as a noncontrolling interest. In connection with the Series A Agreement and this Terns China investment, the Company also issued an option to the LAV PRC Entities to convert their interest in the China Subsidiaries into an interest in Terns Cayman (the LAV Option). Series B Preferred Stock In October 2018, the Company entered into a Series B convertible preferred share purchase agreement (Series B Agreement), whereby the Company issued an aggregate of 2,384,195 shares of Series B convertible preferred stock at $ 30.80 per share for an aggregate purchase price of $ 73.4 million. Terns China received $ 6.7 million from the LAV PRC Entities in connection with the Series B financing, which is presented as a noncontrolling interest. In connection with the Series B Agreement and this Terns China investment, the LAV Option was to allow the LAV PRC Entities to convert this interest in the China Subsidiaries into an interest in Terns Cayman. LAV Series A and Series B Preferred Stock Options In November 2020, the Chinese government provided approval for entities affiliated with Lilly Asia Ventures (LAV) to exercise the LAV Option. Terns Hong Kong agreed to repurchase all equity interests held by the LAV PRC Entities with proceeds to be used by LAV to purchase shares of Series A convertible preferred stock and Series B convertible preferred stock of the Company (Repurchase). In December 2020, the Company issued 767,857 shares of Series A convertible preferred stock and 216,450 shares of Series B convertible preferred stock to an affiliate of LAV (LAV Affiliate) in exchange for a promissory note with a principal amount equal to the original investment by LAV in Terns China (LAV Series A and Series B Promissory Note). The LAV Series A and Series B Promissory Note was repaid through proceeds of the Repurchase which was completed in January 2021. Series C Preferred Stock In December 2020, the Company entered into a Series C preferred stock purchase agreement (Series C Convertible Preferred Stock Financing) whereby it issued an aggregate of 7,500,665 shares of Series C convertible preferred stock at $ 11.65 per share for gross proceeds of $ 87.4 million, which includes shares issued upon conversion of the 2020 Notes. In connection with the Series C Convertible Preferred Stock Financing, the 2020 Notes, totaling unpaid principal and accrued interest of $ 15.9 million, converted into 1,366,820 shares of Series C convertible preferred stock. Furthermore, in December 2020, as part of the effective conversion of the Bridge Loan, the Company issued LAV an aggregate of 167,159 shares of Series C convertible preferred stock. Series A convertible preferred stock, Series B convertible preferred stock and Series C convertible preferred stock are collectively referred to as “convertible preferred stock.” As of December 31, 2020, convertible preferred stock consisted of the following: December 31, 2020 (in thousands, except share amounts) Convertible Convertible Carrying Liquidation Common Series A convertible preferred stock 40,000,000 2,857,142 $ 30,000 $ 30,000 2,857,142 Series B convertible preferred stock 36,409,088 2,600,645 68,995 80,100 5,721,423 Series C convertible preferred stock 111,619,996 7,500,665 87,038 87,368 7,500,665 Total convertible preferred stock 188,029,084 12,958,452 $ 186,033 $ 197,468 16,079,230 In connection with the IPO, all the outstanding shares of convertible preferred stock converted into common stock and the Company does not have any shares of preferred stock outstanding as of September 30, 2021 .

Common Stock and Stock-Based Co

Common Stock and Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Common Stock and Stock-Based Compensation	5. Common Stock and Stock-Based Compensation As of each balance sheet date, the Company had reserved shares of common stock for issuance in connection with the following: September 30, 2021 December 31, 2020 Conversion of outstanding shares of convertible preferred stock — 16,079,230 Options outstanding under incentive award plans 3,556,043 2,466,670 Shares available for future grant under incentive award plans 1,164,490 17,556 Shares available for future grant under employee stock purchase plans 240,000 — Total shares reserved 4,960,533 18,563,456 Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends , if any, as may be declared by the Company’s board of directors, subject to the preferential dividend rights of the convertible preferred stock. Through September 30, 2021 , no cash dividends have been declared or paid by the Company. Stock-Based Compensation The Company has two stock-based compensation plans, the 2017 Incentive Award Plan (the “2017 Plan”) and the 2021 Incentive Award Plan (the “2021 Plan”) which was adopted in February 2021. Each plan, while effective, authorizes the granting of equity awards to employees and directors of the Company, as well as non-employee consultants. Stock options granted to employees and nonemployees under the plans generally vest over four years and allows the holder of the option to purchase common stock at a stated exercise price. Options granted under the plans generally expire ten years after the date of grant. The Company recognizes the stock-based compensation expense over the requisite service period of the individual grantees, which generally equals the vesting period. 2021 Incentive Award Plan In January 2021, the Company's board of directors approved the 2021 Plan which permits the granting of incentive stock options, nonqualified stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance bonus awards, performance stock unit awards and other stock awards to employees, directors, officers and consultants. In February 2021, 2,400,007 shares were authorized for issuance under the 2021 Plan. The 2021 Plan is the successor to the 2017 Incentive Award Plan and no additional awards may be issued from the 2017 Plan. However, the 2017 Plan will continue to govern the terms and conditions of the outstanding awards granted under this plan. Shares of common stock subject to awards granted under the 2017 Plan that are forfeited or lapse unexercised and which following the effective date of the 2021 Plan are not issued under the 2017 Plan will be available for issuance under the 2021 Plan. As of September 30, 2021, 1,164,490 shares of the Company’s common stock were available for future grants under the 2021 Plan. 2021 Employee Stock Purchase Plan The 2021 Employee Stock Purchase Plan (the “2021 ESPP”) was approved by the Company’s board of directors in January 2021. In February 2021, a total of 240,000 shares were initially reserved for issuance under this plan, which shall be cumulatively increased on the first day of each year beginning in 2022 and ending in 2031 equal to the lesser of (i) 1 % of the shares outstanding (on an as converted basis) on the last day of the immediately preceding fiscal year and (ii) such number of shares as may be determined by the Board. Stock Options The following table summarizes the stock option activity for all stock plans during the nine months ended September 30, 2021: Number Weighted- Weighted- Aggregate (in years) (in thousands) Outstanding as of December 31, 2020 2,466,670 $ 8.03 9.61 $ 21,678 Granted 1,383,480 11.92 Exercised ( 151,678 ) 5.92 831 Forfeited ( 142,429 ) 7.25 Outstanding as of September 30, 2021 3,556,043 $ 9.75 9.32 $ 4,501 Exercisable, September 30, 2021 1,864,855 $ 8.32 8.94 $ 3,923 Vested and expected to vest, September 30, 2021 3,556,043 $ 9.75 9.32 $ 4,501 The aggregate intrinsic value of stock options is calculated as the difference between the exercise price of the stock options and the fair value of the Company’s common stock for those stock options that had exercise prices lower than the fair value of the Company’s common stock. As of September 30, 2021, there was $ 31.0 million of unrecognized stock-based compensation expense related to unvested stock options which is estimated to be recognized over a period of 3.22 years. The Company estimated the fair value of options granted using a Black-Scholes option pricing model with the following assumptions presented on a weighted average basis: Nine Months Ended September 30, 2021 2020 Expected option life 6.03 6.02 Expected volatility 76.59 % 61.96 % Risk-free interest rate 1.12 % 0.43 % Expected dividend yield — % — % Fair value of underlying common stock $ 11.92 $ 20.72 Fair value of option $ 7.87 $ 16.14 Expected dividend yield is based on the fact that the Company has never paid cash dividends and does not expect to pay any cash dividends in the foreseeable future. Restricted Stock The following table summarizes the stock award activity for all stock plans during the nine months ended September 30, 2021: Number Grant-Date Unvested restricted common stock as of December 31, 2020 83,334 $ 1.96 Vested ( 71,429 ) 1.96 Forfeited ( 11,905 ) 1.96 Unvested restricted common stock as of September 30, 2021 — $ — As of September 30, 2021 , there was no unrecognized stock-based compensation expense related to restricted stock granted by the Company. Stock-Based Compensation Expense Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Research and development expense $ 401 $ 84 $ 1,374 $ 228 General and administrative expense 1,454 429 4,222 677 Total stock-based compensation expense $ 1,855 $ 513 $ 5,596 $ 905

Income Tax

Income Tax	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Tax	6. Income Tax The Company recorded income tax expense for the three months ended September 30, 2021 of less than $ 0.1 million and of $ 0.1 million for the three months ended September 30, 2020. The expenses are primarily related to foreign income tax expenses from China. The Company recorded income tax expense for the nine months ended September 30, 2021 of $ 0.1 million and of $ 0.1 million for the nine months ended September 30, 2020. The expenses are primarily related to foreign income tax expenses from China. The Company includes interest and penalties related to unrecognized tax benefits within the provision for income taxes. As of September 30, 2021 and 2020, the total amount of gross interest accrued and penalties was nominal.

Net Loss Per Common Share

Net Loss Per Common Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share of Common Stock	7. Net Loss Per Share of Common Stock Basic and diluted net loss per share of common stock were calculated as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands, except share and per share amounts) 2021 2020 2021 2020 Numerator: Net loss $ ( 11,835 ) $ ( 11,591 ) $ ( 35,910 ) $ ( 30,642 ) Net loss attributable to noncontrolling interest — ( 156 ) — ( 518 ) Net loss attributable to common stockholders $ ( 11,835 ) $ ( 11,435 ) $ ( 35,910 ) $ ( 30,124 ) Denominator: Weighted average common stock outstanding, basic and diluted 25,148,336 302,336 21,842,706 270,463 Net loss per share attributable to common $ ( 0.47 ) $ ( 37.82 ) $ ( 1.64 ) $ ( 111.38 ) The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each period end, from the computation of diluted net loss attributable to common stockholders per share of common stock for the periods indicated because including them would have had an anti-dilutive effect: September 30, 2021 2020 Options to purchase common stock 3,556,043 940,034 Restricted common stock — 83,334 Convertible preferred stock (as converted to common stock) — 7,334,518 Options to purchase convertible preferred stock (as converted to common stock) — 984,306 Total 3,556,043 9,342,192

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	8. Commitments and Contingencies Lease Agreements Future minimum lease payments due under operating leases as of September 30, 2021 are as follows: (in thousands) Operating Leases 2021 $ 175 2022 675 2023 652 2024 559 2025 and thereafter — Total $ 2,061 Contingencies From time to time, the Company may have certain contingent liabilities that arise in the ordinary course of business. The Company accrues a liability for such matters when it is probable that future expenditures will be made, and such expenditures can be reasonably estimated. For all periods presented, the Company was not a party to any pending material litigation or other material legal proceedings.

Assignment, License and Collabo

Assignment, License and Collaboration Agreements	9 Months Ended
	Sep. 30, 2021
Assignment License And Collaboration Agreements [Abstract]
Assignment, License and Collaboration Agreements	9. Assignment, License and Collaboration Agreements License Agreements TERN-101 License Agreement with Eli Lilly In February 2018, the Company entered a worldwide exclusive license agreement with Eli Lilly and Company (Lilly) (Lilly FXR 2018 License Agreement). Under the terms of the Lilly FXR 2018 License Agreement, Lilly granted the Company an exclusive, royalty-bearing license to make, have made, use, offer for sale, sell, import, and have imported, including all rights to develop, manufacture, and commercialize covered products in the field in the territory and a sublicensing right that allows the Company to grant sublicenses to affiliates and third parties to perform any portion of the development, manufacture, and commercialization of covered products. The Company is required to use commercially reasonable efforts to meet development event milestones, develop the covered product in the field in mainland China and commercialize the covered product in the field in mainland China. The Company agreed to pay Lilly up to an aggregate of $ 6.0 million in pre-specified development milestones for the first covered product in mainland China, and up to an aggregate of $ 50.0 million in pre-specified development milestones for the first covered product in ex-mainland China. The Company also agreed to pay Lilly tiered royalties calculated on a calendar year basis, in the mid-single digits to low teens on net sales ranging from the low hundreds of millions of dollars to the low billions of dollars. The Lilly FXR 2018 License Agreement expires upon expiry of the last remaining royalty obligation for a licensed product. As of September 30, 2021 , the Company has no t paid any amounts under the agreement and no milestones have been achieved. The Company has no t recorded any research and development expense during the three and nine months ended September 30, 2021 and 2020 related to this agreement. TERN-201 License Agreement with Eli Lilly In March 2018, the Company entered into an exclusive license agreement with Lilly (Lilly VAP-1 2018 License Agreement). Under the terms of the Lilly VAP-1 2018 License Agreement, Lilly granted the Company an exclusive, royalty-bearing license to make, have made, use, offer for sale, sell, import, and have imported, including all rights to develop, manufacture, and commercialize covered products and a sublicensing right that allows the Company to grant sublicenses to affiliates and third parties to perform any portion of the development, manufacture, and commercialization of covered products. The Company will remain directly responsible for all amounts owed to Lilly, regardless of sublicenses. The Company is required to use commercially reasonable efforts to meet development events according to achievement due dates and commercialize the covered product in the field in the major markets. The Company paid Lilly a non-refundable, non-creditable upfront payment of $ 4.0 million, which was recorded as research and development expense in the Company’s statement of operations and comprehensive loss for the year ended December 31, 2018. In addition, pursuant to the terms of the Lilly VAP-1 2018 License Agreement, the Company agreed to pay Lilly up to an aggregate of $ 74.0 million in pre-specified development milestones for the first covered product, and up to an aggregate of $ 30.0 million in pre-specified development milestones for the second indication of a covered product. The Company must also pay Lilly tiered royalties calculated on a calendar year basis, in the mid-single digits to mid-teens on net sales ranging from the high tens of millions of dollars to the low billions of dollars. The Lilly VAP-1 2018 License Agreement expires upon expiry of the last remaining royalty obligation for a licensed product. As of September 30, 2021 , the Company has paid $ 4.0 million to Lilly. No development milestones have been met as of September 30, 2021 . The Company has no t recorded any research and development expense during the three and nine months ended September 30, 2021 and 2020 related to this agreement. Assignment Agreement In June 2019, the Company entered into an assignment agreement with Vintagence Biotechnology Ltd. (Vintagence) (Vintagence 2019 Assignment Agreement). Under the terms of the Vintagence 2019 Assignment Agreement, Vintagence assigned and agreed to assign to the Company any and all worldwide rights, title, and interest in and to the Vintagence technology and gave Terns a sublicensing right that allows the Company to grant sublicenses to any of its affiliates and/or to licensees or contractors to perform any portion of the development, manufacture, and/or commercialization of covered compounds or covered products. The Company will remain directly responsible for all amounts owed to Vintagence under this agreement, regardless of sublicenses. The Company is required to use commercially reasonable efforts to commercialize the covered product in the field in the major markets. The Company paid Vintagence a non-refundable, non-creditable upfront payment of $ 0.7 million, which was recorded as research and development expense in the Company’s statements of operations and comprehensive loss for the year ended December 31, 2019. In addition, pursuant to the terms of the Vintagence 2019 Assignment Agreement, the Company agreed to pay Vintagence up to CNY 205.0 million in development milestones for the first covered product. The term of the Vintagence 2019 Assignment Agreement will continue in effect on a country-by-country basis until all milestone payments are made. The Company has the right to terminate the agreement in its entirety or on a covered product-by-covered product and country-by-country basis, in its sole discretion by giving 60 days advance written notice to Vintagence. As of September 30, 2021 , the Company has paid $ 2.2 million to Vintagence which includes a milestone payment of $ 1.5 million in connection with the Company’s IND filing for TERN-501 in December 2020. The Company has no t recognized any research and development expense during the three and nine months ended September 30, 2021 and 2020, respectively, related to this agreement. Hansoh Option and License Agreement In July 2020, the Company entered into an exclusive option and license agreement with Hansoh (Shanghai) Healthtech Co., Ltd. (Hansoh Healthtech) and Jiangsu Hansoh Pharmaceutical Group Company Ltd. (Jiangsu Hansoh) (collectively, Hansoh) (Hansoh 2020 Option and License Agreement). Under the terms of the Hansoh 2020 Option and License Agreement, the Company granted Hansoh an exclusive, non-transferable, non-sublicensable, fully-paid, royalty-free license to conduct preliminary studies on the licensed compound with an option to exclusively license the same for development and commercialization of licensed products in all prophylactic, palliative, therapeutic and/or diagnostic uses in connection with all human diseases and disorders (including development and research activities on animal models thereof) in the field of oncology, including all types of cancers (Field) in mainland China, Taiwan, Hong Kong and Macau (collectively, the Territory). Upon Hansoh’s exercising the option, the Company will grant to Hansoh and its affiliates, an irrevocable, royalty-bearing license, with the right to sublicense to exploit licensed compound and licensed products in the Field, defined as in the Territory. Hansoh is required to pay the Company a refundable, non-creditable upfront payment of $ 1.0 million, provided that in the event Hansoh elects to not exercise the option, the Company shall refund the amount of the upfront payment within six months from the expiration or termination of the option period. If the Company does not pay the refund amount within six months, the refund amount will be regarded as a debt owed by the Company to Hansoh, secured against the number of common shares as is equal to the refund amount divided by the share price of such shares issued by the Company in the latest equity financing round before the refund amount is due. Interest on the refund amount is at a rate equal to 5 % per annum over the then-current applicable federal rate, compounded annually and will continue to accrue until paid. Interest shall be computed on the basis of a year of 365 days for the actual number of days elapsed. The entire amount of accrued but unpaid interest and all outstanding principal shall be due and payable on or before the close of business on the fifth anniversary of the last day of the refund period. The Company received an upfront payment of $ 0.8 million during the year ended December 31, 2020, which is recognized as a refund liability on the balance sheet. The upfront payment is included in the Company’s condensed consolidated balance sheet as of September 30, 2021 and is presented within accrued expenses and other current liabilities. The upfront payment and future payments are all constrained as of September 30, 2021. In addition, pursuant to the Hansoh 2020 Option and License Agreement, Hansoh has agreed to pay the Company up to $ 67.0 million in pre-specified clinical, regulatory and sales milestones. Hansoh must also pay the Company royalties in the mid-single digits based on net sales of all licensed products. The term of the Hansoh 2020 Option and License Agreement will continue until the end of the last-to-expire royalty term. As of September 30, 2021 , no milestones have been met.

Organization, Basis of Presen_2

Organization, Basis of Presentation and Summary of Significant Accounting Policies (Policies)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Basis of Presentation	Basis of Presentation The accompanying condensed consolidated financial statements are prepared in accordance with accounting principles generally accepted in the United States of America (U.S. GAAP) and include the accounts of Terns and its wholly owned subsidiaries Terns U.S. Opco and Terns Hong Kong and its wholly owned subsidiaries Terns China and Terns Suzhou. Prior period reflects a variable interest in Terns China in which Terns had a majority interest and was the primary beneficiary. The noncontrolling interest attributable to the Company’s variable interest entity (VIE) is presented as a separate component from stockholders’ equity (deficit) in the condensed consolidated balance sheets, and a noncontrolling interest in the condensed consolidated statements of operations and comprehensive loss and condensed consolidated statements of noncontrolling interest, convertible preferred stock and stockholders’ equity (deficit). The Company’s condensed consolidated financial statements have been prepared in conformity with U.S. GAAP. All intercompany balances and transactions have been eliminated in consolidation.
Initial Public Offering	Initial Public Offering In February 2021, the Company completed an initial public offering (the “IPO”) of 8,625,000 shares of its common stock, including the exercise in full by the underwriters of their option to purchase up to 1,125,000 additional shares of common stock, for net proceeds of $ 133.0 million, after deducting underwriting discounts and commissions and offering expenses, and its shares started trading on the Nasdaq Global Select Market under the ticker symbol “TERN.” Upon closing of the IPO, all of the Company's outstanding shares of convertible preferred stock automatically converted into an aggregate of 16,079,230 shares of common stock.
Certificate of Incorporation	Certificate of Incorporation Prior to the IPO, the Company’s certificate of incorporation adopted in December 2020 in connection with the Domestication (the “December 2020 Charter”) authorized the Company to issue the following shares of capital stock: (i) 299,700,000 shares of common stock, (ii) 40,000,000 shares of Series A convertible preferred stock, (iii) 36,409,088 shares of Series B convertible preferred stock, and (iii) 111,619,996 shares of Series C convertible preferred stock. All classes of stock under the December 2020 Charter were authorized at a par value of $ 0.0001 . In February 2021, the Company’s amended and restated certificate of incorporation filed with the Secretary of State of the State of Delaware became effective in connection with the closing of the IPO. Under the amended and restated certificate of incorporation, the Company is authorized to issue 150,000,000 shares of common stock and 10,000,000 shares of preferred stock. All classes of stock have a par value of $ 0.0001 .
Reverse Stock Split	Reverse Stock Split In January 2021, the Company filed an amended and restated certificate of incorporation to effectuate a reverse split of shares of the Company’s common stock and convertible preferred stock on a 1 -for-14 basis (the “Reverse Stock Split”). The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock, options to purchase common stock and per share amounts contained in the condensed consolidated financial statements have been retroactively adjusted to give effect to the Reverse Stock Split for all periods presented.
Variable Interest Entity	Variable Interest Entity The Company consolidates a VIE where it has been determined that the Company is the primary beneficiary of the entity’s operations. The Company has considered its relationships with a certain entity to determine whether the Company has a variable interest in that entity, and if so, whether the Company is the primary beneficiary of the relationship. U.S. GAAP requires VIEs to be consolidated if an entity’s interest in the VIE is a controlling financial interest. Under the variable interest model, a controlling financial interest is determined based on which entity, if any, has (i) the power to direct the activities of the VIE that most significantly impacts the VIE’s economic performance and (ii) the obligations to absorb losses that could potentially be significant to the VIE or the right to receive benefits from the VIE that could potentially be significant to the VIE. Management performs ongoing reassessments of whether changes in the facts and circumstances regarding the Company’s involvement with a VIE will cause the consolidation conclusion to change. The consolidation status of a VIE may change as a result of such reassessments. Changes in consolidation status are applied prospectively in accordance with U.S. GAAP.
Impact of the COVID-19 Pandemic	Impact of the COVID-19 Pandemic The COVID-19 pandemic is rapidly evolving. The COVID-19 virus and new variants that emerge continue to impact countries worldwide, including the United States and China where the Company has business operations. The extent of the impact of the COVID-19 pandemic on business, operations and development timelines and plans remains uncertain, and will depend on certain developments, including the duration and spread of the outbreak and its impact on the Company’s development activities, planned clinical trial enrollment, future trial sites, contract research organizations (CROs), third-party manufacturers and other third parties with whom the Company conducts business, as well as its impact on regulatory authorities and the Company’s key scientific and management personnel. The ultimate impact of the COVID-19 pandemic or a similar health epidemic is highly uncertain and subject to change. To the extent possible, the Company is conducting business as usual, with necessary or advisable modifications to employee travel and to the on-site and in-person activities of the Company's personnel. The Company will continue to actively monitor the rapidly evolving situation related to the COVID-19 pandemic and may take further actions that alter the Company’s operations, including those that may be required by federal, state or local authorities in the United States and China, or that the Company determines are in the best interest of its employees and other third parties with whom the Company conducts business. At this point, the extent to which the COVID-19 pandemic may affect the Company’s business, operations and development timelines and plans, including the resulting impact on expenditures and capital needs, remains uncertain.
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with U.S. GAAP requires management to make estimates and assumptions that affect the reported amounts of assets and liabilities at the date of the financial statements and reported amounts of expenses during the reporting period. Significant estimates and assumptions made in the accompanying consolidated financial statements include, but are not limited to, the estimates for accruals of research and development expenses, accrual of research contract costs, unrecognized tax benefits, fair value of common stock and stock option valuations. On an ongoing basis, the Company evaluates its estimates and judgments, using historical and anticipated results and trends and on various other assumptions that management believes to be reasonable under the circumstances. Actual results could differ from those estimates.
Unaudited Interim Financial Information	Unaudited Interim Financial Information The accompanying unaudited condensed consolidated balance sheet as of September 30, 2021, the unaudited condensed consolidated statements of operations and comprehensive loss for the three and nine months ended September 30, 2021 and 2020, the unaudited condensed consolidated statements of noncontrolling interest, convertible preferred stock and stockholders’ equity (deficit) for the three and nine months ended September 30, 2021 and 2020, the unaudited condensed consolidated statements of cash flows for the nine months ended September 30, 2021 and 2020, and the related 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 unaudited condensed consolidated financial statements should be read in conjunction with the Company’s audited consolidated financial statements and the notes thereto in the Company’s Annual Report on Form 10-K (“Annual Report”) for the fiscal year ended December 31, 2020, as filed with the SEC on March 30, 2021. There have been no significant changes to the Company's significant accounting policies described in Note 1, Organization, Basis of Presentation and Summary of Significant Accounting Policies, in Notes to Consolidated Financial Statements in Item 8 of Part II of the Form 10-K for the fiscal year ended December 31, 2020.
Cash, Cash Equivalents, Restricted Cash and Marketable Securities	Cash, Cash Equivalents, Restricted Cash and Marketable Securities Cash and cash equivalents consist of standard checking accounts and money market funds. The Company considers all highly liquid investments with an original maturity of 90 days or less at the date of purchase to be cash equivalents. Restricted cash represents a security deposit related to a lease. The Company classifies as available-for-sale marketable securities with a remaining maturity when purchased of greater than three months. The Company’s marketable securities are maintained by investment managers and consist of government securities, corporate debt securities, asset-backed securities and commercial paper. Debt securities are carried at fair value with the unrealized gains and losses included in other comprehensive loss as a component of stockholders’ equity (deficit) until realized. Any premium arising at purchase is amortized to the earliest call date and any discount arising at purchase is accreted to maturity. Amortization and accretion of premiums and discounts are recorded in interest income and/or expense. Realized gains and losses on debt securities are determined using the specific identification method and are included in other income (expense), net. If any adjustment to fair value reflects a decline in value of the investment, the Company considers all available evidence to evaluate the extent to which the decline is “other-than-temporary” and, if so, marks the investment to market through a charge to the Company’s condensed consolidated statements of operations and comprehensive loss. The fair value and amortized cost of marketable securities by major security type as of September 30, 2021 is as follows: September 30, 2021 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Money market funds $ 39,213 $ — $ — $ 39,213 U.S. government securities 21,123 5 ( 8 ) 21,120 Non-U.S. government securities 11,203 — ( 1 ) 11,202 Corporate debt securities 44,161 10 ( 11 ) 44,160 Commercial paper 35,963 — — 35,963 Total $ 151,663 $ 15 $ ( 20 ) $ 151,658 Classified as: Cash equivalents $ 39,213 Marketable securities 112,445 Total $ 151,658 The Company did no t have any marketable securities for the year ended December 31, 2020. The reconciliation of cash, cash equivalents and restricted cash reported within the applicable balance sheet line items that sum to the total of the same such amount shown in the consolidated statements of cash flows is as follows: September 30, (in thousands) 2021 2020 Cash and cash equivalents $ 64,751 $ 13,756 Restricted cash, non-current — 48 Total cash, cash equivalents and restricted cash $ 64,751 $ 13,804
Classification of Convertible Preferred Stock and Presentation of Noncontrolling Interest	Classification of Convertible Preferred Stock and Presentation of Noncontrolling Interest The holders of Series A, Series B and Series C convertible preferred stock, which were outstanding prior to the IPO, had certain liquidation rights in the event of a deemed liquidation that, in certain situations, were not solely within the control of the Company and would call for the redemption of the then outstanding convertible preferred stock. Therefore, the Series A, Series B and Series C convertible preferred stock were classified outside of shareholders’ equity (deficit) on the condensed consolidated balance sheets as of December 31, 2020. In February 2021, upon the completion of the IPO, all the outstanding shares of convertible preferred stock converted into common stock and the Company does not have any shares of preferred stock outstanding. The Company recognizes a noncontrolling interest related to VIEs in which the Company is the primary beneficiary as equity in the condensed consolidated financial statements separate from the parent entity’s equity. The net loss attributable to noncontrolling interest is included in net loss in the condensed consolidated statements of operations and comprehensive loss. Changes in the parent entity’s ownership interest in a subsidiary that do not result in deconsolidation are treated as equity transactions if the parent entity retains its controlling financial interest. In addition, when a subsidiary is deconsolidated, any retained noncontrolling equity investment in the former subsidiary will be initially measured at fair value and the difference between the carrying value and fair value of the retained interest will be recorded as a gain or loss. Terns China, the Company’s VIE, was established as a financing subsidiary to allow investment by Lilly Asia Ventures (LAV) investment entities: Suzhou Litai Equity Investment Centre (Limited Partnership) (PRC) and Suzhou Lirui Equity Investment Centre (Limited Partnership) (PRC), collectively referred to as the “LAV PRC Entities”. The Company’s board of directors has the unilateral ability to control the Terns China board of directors. Net losses of the China Subsidiaries have been allocated based on their ownership percentage to the LAV PRC Entities’ noncontrolling interest and are reflected in the condensed consolidated statements of operations and comprehensive loss. The noncontrolling interest is classified outside of stockholders’ equity (deficit) on the condensed consolidated balance sheets as it is redeemable for cash based on an investor option after a specified date. In December 2020, the LAV PRC Entities exercised their option resulting in the conversion of all of the equity interests in Terns China held by the LAV PRC Entities into shares of the Company’s preferred stock (the “China Conversion”). Following the completion of the China Conversion, Terns China became a wholly owned subsidiary of the Company. The Company does not currently anticipate any further direct third-party investments into Terns China and Terns China will only act as an operating subsidiary for the Company’s business activities in China.
Research and Development Expenses	Research and Development Expenses Research and development costs are expensed as incurred. Research and development expenses consist of costs incurred to discover, research and develop drug candidates, including personnel expenses, stock-based compensation expense, allocated facility-related and depreciation expenses, third-party license fees and external costs, including fees paid to consultants and contract research organizations, or CROs, in connection with nonclinical studies and clinical trials and other related clinical trial fees, such as for investigator grants, patient screening, laboratory work, clinical trial database management, clinical trial material management and statistical compilation and analysis. Non-refundable prepayments for goods or services that will be used or rendered for future research and development activities are recorded as prepaid expenses. Such amounts are recognized as an expense as the goods are delivered or the related services are performed, or until it is no longer expected that the goods will be delivered, or the services rendered. Costs incurred in obtaining technology licenses are charged immediately to research and development expense if the technology licensed has not reached technological feasibility and has no alternative future uses. The Company has from time to time entered into various research and development and other agreements with commercial firms, researchers, universities and others for provisions of goods and services. These agreements are generally cancelable, and the related costs are recorded as research and development expenses as incurred. The Company records accruals for estimated ongoing research and development costs. When evaluating the adequacy of the accrued liabilities, the Company analyzes progress of the studies or clinical trials, including the phase or completion of events, invoices received and contracted costs. Significant judgments and estimates are made in determining the accrued balances at the end of any reporting period. Actual results could differ materially from the Company’s estimates. Since inception, the Company’s historical accrual estimates have not been materially different from the actual costs.
Accrued Expenses and Other Current Liabilities	Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities included the following: (in thousands) September 30, 2021 December 31, 2020 Research and development costs $ 1,907 $ 2,800 Refundable contract liability 836 836 Compensation and benefit costs 1,393 1,492 Accrued professional fees 1,092 2,185 Accrued development milestone — 1,531 Other 83 162 Total accrued expenses and other current liabilities $ 5,311 $ 9,006
Income Taxes	Income Taxes The provision for income taxes primarily relates to projected federal, state, and foreign income taxes. To determine the quarterly provision for income taxes, the Company uses an estimated annual effective tax rate, which is generally based on expected annual income and statutory tax rates in the various jurisdictions in which the Company operates. In addition, the tax effects of certain significant or unusual items are recognized discretely in the quarter during which they occur and can be a source of variability in the effective tax rates from quarter to quarter. Income taxes are computed using the asset and liability approach that requires the recognition of deferred tax assets and liabilities for the expected future tax consequences of events that have been recognized in the Company’s financial statements. In estimating future tax consequences, the Company considers all expected future events including the enactment of changes in tax laws or rates. A valuation allowance is recorded, if necessary, to reduce net deferred tax assets to their realizable values if management does not believe it is more likely than not that the net deferred tax assets will be realized. In making such a determination, management considers all available positive and negative evidence, including future reversals of existing taxable temporary differences, projected future taxable income, and ongoing prudent and feasible tax planning strategies in assessing the amount of the valuation allowance. When the Company establishes or reduces the valuation allowance against its deferred tax assets, its provision for income taxes will increase or decrease, respectively, in the period such determination is made. The Company assesses accounting for uncertainty in income taxes by modeling for the recognition, measurement and disclosure in financial statements any uncertain income tax positions that the Company has taken or expects to take on a tax return. As of each balance sheet date, unresolved uncertain tax positions are reassessed. The Company accrues interest and related penalties, if applicable, on all tax exposures for which reserves have been established consistent with jurisdictional tax laws.
Common Stock Valuation	Common Stock Valuation Due to the absence of an active market for the Company’s common stock prior to the completion of the IPO in February 2021, the Company utilized methodologies to estimate the fair value of its common stock. In determining the fair value of options granted prior to the IPO, the Company has considered the estimated fair value of the common stock as of the measurement date. The estimated fair value of the common stock prior to the IPO was determined at each grant date based upon a variety of factors, including:  the prices at which the Company sold shares of convertible preferred stock and the superior rights and preferences of the convertible preferred stock relative to its common stock at the time of each grant;  the progress of the Company’s research and development programs, including the status and results of clinical and nonclinical studies for its drugs;  the Company’s stage of development and commercialization and its business strategy;  external market conditions affecting the biotechnology industry and trends within the biotechnology industry;  the Company’s financial position, including cash on hand, and its historical and forecasted performance and operating results;  the lack of an active public market for the Company’s common stock and convertible preferred stock;  the likelihood of achieving a liquidity event, such as an IPO or sale of the Company in light of prevailing market conditions; and  the analysis of IPOs and the market performance of similar companies in the biotechnology industry. Significant changes to the key assumptions underlying the factors used could have resulted in different fair values of common stock at each valuation date.
Comprehensive Loss	Comprehensive Loss Comprehensive loss is defined as the change in equity of a business enterprise during a period from transactions and other events and circumstances from non-owner sources.
Stock-Based Compensation	Stock-Based Compensation Stock-based compensation expense, including grants of stock options and restricted stock awards issued under the Company’s equity incentive plan, is measured at the grant date based on the fair value of the awards and is recognized as an expense on a straight-line basis over the requisite service period, which is generally the vesting period. The Company’s determination of the fair value of stock options with time-based vesting utilizes the Black-Scholes option-pricing model. The Company lacks sufficient company-specific historical and implied volatility information. Therefore, it estimates its expected stock volatility based on the historical volatility of a publicly traded set of peer companies and expects to continue to do so until such time as it has adequate historical data regarding the volatility of its own traded stock price. The Company estimates risk-free rates using the implied yield currently available on U.S. Treasury zero-coupon issues with a remaining term equal to the expected term and dividend yield using the Company’s expectations and historical data. The Company uses the simplified method to calculate the expected term of stock option grants. Under the simplified method, the expected term is estimated to be the mid-point between the vesting date and the contractual term of the option. The fair value of each stock option grant is calculated based upon the Company’s common stock valuation on the date of the grant. The Company accounts for forfeitures of stock option grants as they occur.
Net Loss Per Share of Common Stock	Net Loss Per Share of Common Stock The Company follows the two-class method when computing net income (loss) per share of common stock as the Company has issued shares that meet the definition of participating securities. The two-class method determines net income (loss) per share of common stock for each class of common and participating securities according to dividends declared or accumulated and participation rights in undistributed earnings. The two-class method requires income available to common stockholders for the period to be allocated between common and participating securities based upon their respective rights to receive dividends as if all income for the period had been distributed. Basic net income (loss) per share of common stock is computed by dividing the net income (loss) per share of common stock by the weighted average number of shares of common stock outstanding for the period. Diluted net income (loss) per share of common stock is computed by adjusting net income (loss) to reallocate undistributed earnings based on the potential impact of dilutive securities. Diluted net loss per share of common stock is computed by dividing the diluted net loss by the weighted average number of shares of common stock outstanding for the period, including potential dilutive shares. For purposes of this calculation, outstanding stock options and convertible preferred stock are considered potential dilutive shares. The Company’s convertible preferred stock outstanding prior to the IPO contractually entitled the holders of such shares to participate in dividends but did not contractually require the holders of such shares to participate in losses of the Company. Accordingly, in periods in which the Company reports a net loss, such losses are not allocated to such securities. In periods in which the Company reports a net loss, diluted net loss per share of common stock is the same as basic net loss per share of common stock, since dilutive shares are not assumed to have been issued if their effect is anti-dilutive. The Company reported a net loss for the three and nine months ended September 30, 2021 and 2020 .
Deferred Offering Costs	Deferred Offering Costs The Company capitalizes certain legal, professional accounting and other third-party fees that are directly associated with in-process equity financings as deferred offering costs until such financings are consummated. After consummation of the equity financing, these costs are recorded as a reduction to the carrying value of stockholders’ equity (deficit) as a reduction of additional paid-in capital or equity generated as a result of such 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.
Recent Accounting Pronouncements	Recent Accounting Pronouncements From time to time, new accounting pronouncements are issued by the FASB or other standard setting bodies. The Company is an emerging growth company as defined in the Jumpstart Our Business Startups Act of 2012, as amended (JOBS Act). Under the JOBS Act, emerging growth companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected to use this exemption to delay adopting new or revised accounting standards until such time as those standards apply to private companies. Where allowable, the Company has early adopted certain standards as described below. Recently Adopted Accounting Pronouncements In June 2018, the FASB issued ASU 2018-07, Compensation - Stock Compensation (Topic 718): Improvements to Non-employee Share-Based Payment Accounting (“ASU 2018-07”). ASU 2018-07 primarily expands the scope of Topic 718 to include share-based payment transactions for acquiring goods and services from non-employees. ASU 2018-07 is effective for fiscal years beginning after December 15, 2018, including interim periods within that fiscal year. The Company adopted ASU 2018-07 on January 1, 2021 , and the adoption of this standard did not have an impact on the Company’s consolidated financial statements. Recently Issued Accounting Pronouncements Not Yet Adopted In February 2016, the FASB issued ASU 2016-02, Leases (Topic 842) (ASU 2016-02), which sets out the principles for the recognition, measurement, presentation and disclosure of leases for both parties to a contract (i.e., lessees and lessors). The new standard requires lessees to apply a dual approach, classifying leases as either finance or operating leases based on the principle of whether or not the lease is effectively a financed purchase by the lessee. This classification will determine whether lease expense is recognized based on an effective interest method or on a straight-line basis over the term of the lease. A lessee is also required to record a right-of-use asset and a lease liability for all leases with a term of greater than 12 months regardless of their classification. Leases with a term of 12 months or less may be accounted for similar to existing guidance for operating leases today. For non-public entities, ASU 2016-02 is effective for annual reporting periods, and interim periods within those fiscal years, beginning after December 15, 2021, and early adoption is permitted. Under the JOBS Act, emerging growth companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected to use this exemption to delay adopting ASU 2016-02. The Company is in the process of completing its review of its existing lease agreements under Topic 842 and does not expect the adoption of ASU 2016-02 to have a material impact on its financial position, results of operations or cash flows. In June 2016, the FASB issued ASU 2016-13, Financial Instruments-Credit Losses (Topic 326): Measurement of Credit Losses on Financial Instruments (ASU 2016-13), which requires the measurement and recognition of expected credit losses for financial assets held at amortized cost. ASU 2016-13 replaces the existing incurred loss impairment model with an expected loss methodology, which will result in more timely recognition of credit losses. For non-public entities, ASU 2016-13 is effective for annual reporting periods, and interim periods within those fiscal years, beginning after December 15, 2022. Under the JOBS Act, emerging growth companies have extended transition periods available for complying with new or revised accounting standards. The Company has elected to use this exemption to delay adopting ASU 2016-13. The Company is currently in the process of evaluating the impact of the adoption of ASU 2016-13 on its consolidated financial statements.

Organization, Basis of Presen_3

Organization, Basis of Presentation and Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Schedule of Fair Value And Amortized Cost of Marketable Securities	The fair value and amortized cost of marketable securities by major security type as of September 30, 2021 is as follows: September 30, 2021 (in thousands) Amortized Cost Unrealized Gains Unrealized Losses Fair Value Money market funds $ 39,213 $ — $ — $ 39,213 U.S. government securities 21,123 5 ( 8 ) 21,120 Non-U.S. government securities 11,203 — ( 1 ) 11,202 Corporate debt securities 44,161 10 ( 11 ) 44,160 Commercial paper 35,963 — — 35,963 Total $ 151,663 $ 15 $ ( 20 ) $ 151,658 Classified as: Cash equivalents $ 39,213 Marketable securities 112,445 Total $ 151,658
Reconciliation of Cash, Cash Equivalents and Restricted Cash	The reconciliation of cash, cash equivalents and restricted cash reported within the applicable balance sheet line items that sum to the total of the same such amount shown in the consolidated statements of cash flows is as follows: September 30, (in thousands) 2021 2020 Cash and cash equivalents $ 64,751 $ 13,756 Restricted cash, non-current — 48 Total cash, cash equivalents and restricted cash $ 64,751 $ 13,804
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities included the following: (in thousands) September 30, 2021 December 31, 2020 Research and development costs $ 1,907 $ 2,800 Refundable contract liability 836 836 Compensation and benefit costs 1,393 1,492 Accrued professional fees 1,092 2,185 Accrued development milestone — 1,531 Other 83 162 Total accrued expenses and other current liabilities $ 5,311 $ 9,006

Fair Value (Tables)

Fair Value (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis	The following tables present information about the Company’s financial assets and liabilities measured at fair value on a recurring basis: Fair Value at September 30, 2021 (in thousands) Level 1 Level 2 Level 3 Total Cash and cash equivalents Cash in bank balances $ 25,538 $ — $ — $ 25,538 Money market funds 39,213 — — 39,213 Total cash and cash equivalents $ 64,751 $ — $ — $ 64,751 Marketable securities U.S. government securities $ — $ 21,120 $ — $ 21,120 Non-U.S. government securities — 11,202 — 11,202 Corporate debt securities — 44,160 — 44,160 Commercial paper — 35,963 — 35,963 Total marketable securities $ — $ 112,445 $ — $ 112,445 Fair Value at December 31, 2020 (in thousands) Level 1 Level 2 Level 3 Total Assets: Cash and cash equivalents $ 74,854 $ — $ — $ 74,854 Total $ 74,854 $ — $ — $ 74,854 Liabilities: Loans payable $ — $ — $ 12,880 $ 12,880 Total $ — $ — $ 12,880 $ 12,880
Schedule of Aggregate Fair Value of Marketable Securities	The aggregate fair value of marketable securities as of September 30, 2021, by contractual maturity, are as follows: (in thousands) Fair Value Due in one year or less $ 77,555 Due after one year through two years 34,890 Total marketable securities $ 112,445

Loans Payable (Tables)

Loans Payable (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Schedule of Loans Payable Reported at Fair Value and Measured on Recurring Basis	The following table provides the loans payable reported at fair value and measured on a recurring basis: (in thousands) Loans Payable Balance at December 31, 2019 $ — Issuance of 2020 Notes and Bridge Loan 16,800 Issuance of repurchase payable for the Lilly Asia Ventures option exercise 10,771 Issuance of loans payable for conversion settlement of the Bridge Loan 2,109 Conversion of 2020 convertible promissory notes to Series C convertible preferred stock ( 17,690 ) Conversion of Bridge Loan to Series C convertible preferred stock ( 2,163 ) Change in fair value of loans payable and other adjustments 3,053 Balance at December 31, 2020 $ 12,880

Convertible Preferred Stock (Ta

Convertible Preferred Stock (Tables)	9 Months Ended
	Sep. 30, 2021
Convertible Preferred Stock [Abstract]
Schedule of Convertible Preferred Stock	Series A convertible preferred stock, Series B convertible preferred stock and Series C convertible preferred stock are collectively referred to as “convertible preferred stock.” As of December 31, 2020, convertible preferred stock consisted of the following: December 31, 2020 (in thousands, except share amounts) Convertible Convertible Carrying Liquidation Common Series A convertible preferred stock 40,000,000 2,857,142 $ 30,000 $ 30,000 2,857,142 Series B convertible preferred stock 36,409,088 2,600,645 68,995 80,100 5,721,423 Series C convertible preferred stock 111,619,996 7,500,665 87,038 87,368 7,500,665 Total convertible preferred stock 188,029,084 12,958,452 $ 186,033 $ 197,468 16,079,230

Common Stock and Stock-Based _2

Common Stock and Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Common Stock Shares Reserved for Issuance	As of each balance sheet date, the Company had reserved shares of common stock for issuance in connection with the following: September 30, 2021 December 31, 2020 Conversion of outstanding shares of convertible preferred stock — 16,079,230 Options outstanding under incentive award plans 3,556,043 2,466,670 Shares available for future grant under incentive award plans 1,164,490 17,556 Shares available for future grant under employee stock purchase plans 240,000 — Total shares reserved 4,960,533 18,563,456
Summary of Stock Option Activity	The following table summarizes the stock option activity for all stock plans during the nine months ended September 30, 2021: Number Weighted- Weighted- Aggregate (in years) (in thousands) Outstanding as of December 31, 2020 2,466,670 $ 8.03 9.61 $ 21,678 Granted 1,383,480 11.92 Exercised ( 151,678 ) 5.92 831 Forfeited ( 142,429 ) 7.25 Outstanding as of September 30, 2021 3,556,043 $ 9.75 9.32 $ 4,501 Exercisable, September 30, 2021 1,864,855 $ 8.32 8.94 $ 3,923 Vested and expected to vest, September 30, 2021 3,556,043 $ 9.75 9.32 $ 4,501
Schedule of Stock Options Weighted Average Assumptions	The Company estimated the fair value of options granted using a Black-Scholes option pricing model with the following assumptions presented on a weighted average basis: Nine Months Ended September 30, 2021 2020 Expected option life 6.03 6.02 Expected volatility 76.59 % 61.96 % Risk-free interest rate 1.12 % 0.43 % Expected dividend yield — % — % Fair value of underlying common stock $ 11.92 $ 20.72 Fair value of option $ 7.87 $ 16.14
Summary of Restricted Stock Award Activity	The following table summarizes the stock award activity for all stock plans during the nine months ended September 30, 2021: Number Grant-Date Unvested restricted common stock as of December 31, 2020 83,334 $ 1.96 Vested ( 71,429 ) 1.96 Forfeited ( 11,905 ) 1.96 Unvested restricted common stock as of September 30, 2021 — $ —
Schedule of Stock-based Compensation Expense	Stock-based compensation expense was classified in the condensed consolidated statements of operations and comprehensive loss as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands) 2021 2020 2021 2020 Research and development expense $ 401 $ 84 $ 1,374 $ 228 General and administrative expense 1,454 429 4,222 677 Total stock-based compensation expense $ 1,855 $ 513 $ 5,596 $ 905

Net Loss Per Common Share (Tabl

Net Loss Per Common Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Schedule of Computation of Basic and Diluted Net Loss per Common Share	Basic and diluted net loss per share of common stock were calculated as follows: Three Months Ended September 30, Nine Months Ended September 30, (in thousands, except share and per share amounts) 2021 2020 2021 2020 Numerator: Net loss $ ( 11,835 ) $ ( 11,591 ) $ ( 35,910 ) $ ( 30,642 ) Net loss attributable to noncontrolling interest — ( 156 ) — ( 518 ) Net loss attributable to common stockholders $ ( 11,835 ) $ ( 11,435 ) $ ( 35,910 ) $ ( 30,124 ) Denominator: Weighted average common stock outstanding, basic and diluted 25,148,336 302,336 21,842,706 270,463 Net loss per share attributable to common $ ( 0.47 ) $ ( 37.82 ) $ ( 1.64 ) $ ( 111.38 )
Schedule of Antidilutive Securities Excluded from Computation of Net Loss per Share	The Company excluded the following potential shares of common stock, presented based on amounts outstanding at each period end, from the computation of diluted net loss attributable to common stockholders per share of common stock for the periods indicated because including them would have had an anti-dilutive effect: September 30, 2021 2020 Options to purchase common stock 3,556,043 940,034 Restricted common stock — 83,334 Convertible preferred stock (as converted to common stock) — 7,334,518 Options to purchase convertible preferred stock (as converted to common stock) — 984,306 Total 3,556,043 9,342,192

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Future Minimum Lease Payments Due Under Operating Leases	Future minimum lease payments due under operating leases as of September 30, 2021 are as follows: (in thousands) Operating Leases 2021 $ 175 2022 675 2023 652 2024 559 2025 and thereafter — Total $ 2,061

Organization, Basis of Presen_4

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Additional Information (Details)	1 Months Ended		9 Months Ended
	Feb. 28, 2021USD ($)$ / sharesshares	Jan. 31, 2021	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares	Oct. 31, 2018$ / shares	Apr. 30, 2017$ / shares
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Convertible preferred stock, shares issued upon conversion	16,079,230			16,079,230
Common stock, authorized	150,000,000		150,000,000	299,700,000
Convertible preferred stock,authorized			10,000,000	188,029,084
Common stock, par value | $ / shares	$ 0.0001		$ 0.0001	$ 0.0001
Convertible preferred stock, par value | $ / shares			$ 0.0001	$ 0.0001
Preferred stock, shares authorized	10,000,000
Preferred stock, par or stated value per share | $ / shares	$ 0.0001
Description of reverse stock split			In January 2021, the Company filed an amended and restated certificate of incorporation to effectuate a reverse split of shares of the Company’s common stock and convertible preferred stock on a 1-for-14 basis (the “Reverse Stock Split”). The par value and the number of authorized shares of the convertible preferred stock and common stock were not adjusted as a result of the Reverse Stock Split. All issued and outstanding common stock, options to purchase common stock and per share amounts contained in the condensed consolidated financial statements have been retroactively adjusted to give effect to the Reverse Stock Split for all periods presented.
Reverse stock split, conversion ratio		0.0714
Marketable securities | $			$ 112,445,000	$ 0
ASU 2018-07
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]			true
Change in accounting principle, accounting standards update, adoption date			Jan. 1, 2021
Change in accounting principle, accounting standards update, immaterial effect [true false]			true
ASU 2016-02
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]			false
Change in accounting principle, accounting standards update, immaterial effect [true false]			true
ASU 2016-13
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Change in accounting principle, accounting standards update, adopted [true false]			false
Series A convertible preferred stock
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Convertible preferred stock, shares issued upon conversion				2,857,142
Convertible preferred stock,authorized				40,000,000
Convertible preferred stock, par value | $ / shares						$ 10.50
Series B convertible preferred stock
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Convertible preferred stock, shares issued upon conversion				5,721,423
Convertible preferred stock,authorized				36,409,088
Convertible preferred stock, par value | $ / shares					$ 30.80
Series C convertible preferred stock
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Convertible preferred stock, shares issued upon conversion				7,500,665
Convertible preferred stock,authorized				111,619,996
Convertible preferred stock, par value | $ / shares				$ 11.65
IPO
Basis Of Presentation And Summary Of Significant Accounting Policies [Line Items]
Number of shares issued	8,625,000
Underwriters option to purchase additional shares	1,125,000
Net proceeds from issuance of common stock | $	$ 133,000,000
Convertible preferred stock, shares issued upon conversion	16,079,230

Organization, Basis of Presen_5

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Fair Value And Amortized Cost of Marketable Securities (Details) $ in Thousands	Sep. 30, 2021USD ($)
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	$ 151,663
Unrealized Gains	15
Unrealized Losses	(20)
Fair Value	151,658
Cash equivalents	39,213
Marketable securities	112,445
Total	151,658
Money Market Funds
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	39,213
Unrealized Gains	0
Unrealized Losses	0
Fair Value	39,213
U.S. government securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	21,123
Unrealized Gains	5
Unrealized Losses	(8)
Fair Value	21,120
Non-U.S. Government Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	11,203
Unrealized Gains	0
Unrealized Losses	(1)
Fair Value	11,202
Corporate Debt Securities
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	44,161
Unrealized Gains	10
Unrealized Losses	(11)
Fair Value	44,160
Commercial Paper
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Amortized Cost	35,963
Unrealized Gains	0
Unrealized Losses	0
Fair Value	$ 35,963

Organization, Basis of Presen_6

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Reconciliation of Cash, Cash Equivalents and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020
Accounting Policies [Abstract]
Cash and cash equivalents	$ 64,751	$ 74,854	$ 13,756
Restricted cash, non-current	0		48
Total cash, cash equivalents and restricted cash	$ 64,751		$ 13,804

Organization, Basis of Presen_7

Organization, Basis of Presentation and Summary of Significant Accounting Policies - Schedule of Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accounting Policies [Abstract]
Research and development costs	$ 1,907	$ 2,800
Refundable contract liability	836	836
Compensation and benefit costs	1,393	1,492
Accrued professional fees	1,092	2,185
Accrued development milestone	0	1,531
Other	83	162
Total accrued expenses and other current liabilities	$ 5,311	$ 9,006

Fair Value - Schedule of Financ

Fair Value - Schedule of Financial Assets and Liabilities Measured at Fair Value on a Recurring Basis (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Assets:
Marketable securities	$ 112,445,000	$ 0
Recurring
Assets:
Total cash and cash equivalents	64,751,000	74,854,000
Marketable securities	112,445,000
Total		74,854,000
Liabilities:
Loans payable		12,880,000
Total		12,880,000
Recurring | Cash in bank balances
Assets:
Total cash and cash equivalents	25,538,000
Recurring | Money Market Funds
Assets:
Total cash and cash equivalents	39,213,000
Recurring | U.S. government securities
Assets:
Marketable securities	21,120,000
Recurring | Non-U.S. Government Securities
Assets:
Marketable securities	11,202,000
Recurring | Corporate Debt Securities
Assets:
Marketable securities	44,160,000
Recurring | Commercial Paper
Assets:
Marketable securities	35,963,000
Recurring | Level 1
Assets:
Total cash and cash equivalents	64,751,000	74,854,000
Total		74,854,000
Recurring | Level 1 | Cash in bank balances
Assets:
Total cash and cash equivalents	25,538,000
Recurring | Level 1 | Money Market Funds
Assets:
Total cash and cash equivalents	39,213,000
Recurring | Level 2
Assets:
Marketable securities	112,445,000
Recurring | Level 2 | U.S. government securities
Assets:
Marketable securities	21,120,000
Recurring | Level 2 | Non-U.S. Government Securities
Assets:
Marketable securities	11,202,000
Recurring | Level 2 | Corporate Debt Securities
Assets:
Marketable securities	44,160,000
Recurring | Level 2 | Commercial Paper
Assets:
Marketable securities	$ 35,963,000
Recurring | Level 3
Liabilities:
Loans payable		12,880,000
Total		$ 12,880,000

Fair Value - Schedule of Aggreg

Fair Value - Schedule of Aggregate Fair Value of Marketable Securities (Details) - USD ($)	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Due in one year or less	$ 77,555,000
Due after one year through two years	34,890,000
Total marketable securities	$ 112,445,000	$ 0

Fair Value - Additional Informa

Fair Value - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021USD ($)
Fair Value Disclosures [Abstract]
Assets, Level 1 to Level 2 transfers	$ 0
Assets, Level 2 to Level 1 Transfers	0
Assets, Transfers into Level 3	0
Assets, Transfers out of Level 3	0
Liabilities, Level 1 to Level 2 transfers	0
Liabilities, Level 2 to Level 1 transfers	0
Liabilities, Transfers into Level 3	0
Liabilities, Transfers out of Level 3	$ 0

Loans Payable - Schedule of Loa

Loans Payable - Schedule of Loans Payable Reported at Fair Value and Measured on Recurring Basis (Details) - USD ($) $ in Thousands	1 Months Ended	12 Months Ended
	May 31, 2020	Dec. 31, 2020
2020 Notes
Short Term Debt [Line Items]
Issuance of 2020 Notes and Bridge Loan	$ 15,000
Conversion of 2020 convertible promissory notes to Series C convertible preferred stock	$ (15,900)
Recurring | Loans Payable
Short Term Debt [Line Items]
Balance		$ 0
Change in fair value of loans payable and other adjustments		3,053
Balance		12,880
Recurring | Loans Payable | 2020 Notes and Bridge Loan
Short Term Debt [Line Items]
Issuance of 2020 Notes and Bridge Loan		16,800
Recurring | Loans Payable | Lilly Asia Ventures Option Exercise
Short Term Debt [Line Items]
Issuance of repurchase payable for the Lilly Asia Ventures option exercise		10,771
Recurring | Loans Payable | Bridge Loan
Short Term Debt [Line Items]
Issuance of loans payable for conversion settlement of the Bridge Loan		2,109
Recurring | Loans Payable | Series C convertible preferred stock | Bridge Loan
Short Term Debt [Line Items]
Conversion of 2020 convertible promissory notes to Series C convertible preferred stock		(2,163)
Recurring | Loans Payable | Series C convertible preferred stock | 2020 Notes
Short Term Debt [Line Items]
Conversion of 2020 convertible promissory notes to Series C convertible preferred stock		$ (17,690)

Loans Payable - Additional Info

Loans Payable - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended		9 Months Ended
	Dec. 31, 2020	May 31, 2020	Sep. 30, 2021	Dec. 29, 2020	Oct. 31, 2018	Apr. 30, 2017
Short Term Debt [Line Items]
Debt Instrument, fair value			$ 0
Convertible preferred stock, shares issued	12,958,452		0
Bridge Loan
Short Term Debt [Line Items]
Debt Instrument, fair value	$ 2,100
Proceeds from issuance of debt		$ 1,800
Debt instrument, interest rate		10.00%
Debt conversion, original debt, amount	1,800
Proceeds from debt payable in different currency, description			payable in renminbi (RMB) at an established USD/RMB exchange rate, based on an average of the previous five working days before May 8, 2020.
Debt conversion to stock, aggregate debt plus accrued interest	$ 1,900
Debt conversion, accrued interest, amount				$ 100
Series C convertible preferred stock
Short Term Debt [Line Items]
Debt conversion, converted instrument, shares		1,366,820
Convertible preferred stock, shares issued	7,500,665
Series C convertible preferred stock | Bridge Loan
Short Term Debt [Line Items]
Debt conversion, converted instrument, shares	167,159
Series A convertible preferred stock
Short Term Debt [Line Items]
Convertible preferred stock, shares issued	2,857,142					2,089,285
Series A convertible preferred stock | LAV Affiliate
Short Term Debt [Line Items]
Convertible preferred stock, shares issued	767,857
Series B convertible preferred stock
Short Term Debt [Line Items]
Convertible preferred stock, shares issued	2,600,645				2,384,195
Series B convertible preferred stock | LAV Affiliate
Short Term Debt [Line Items]
Convertible preferred stock, shares issued	216,450
2020 Notes
Short Term Debt [Line Items]
Proceeds from issuance of debt		$ 15,000
Debt instrument, interest rate		10.00%
Debt conversion, original debt, amount		$ 15,900
Debt conversion to stock, aggregate debt plus accrued interest	$ 15,900
2020 Notes | Series C convertible preferred stock
Short Term Debt [Line Items]
Debt conversion, converted instrument, shares	1,366,820

Loans Payable - Change in Fair

Loans Payable - Change in Fair Value of Loans Payable - Additional Information (Details) - USD ($) $ in Thousands	1 Months Ended	3 Months Ended		9 Months Ended		12 Months Ended
	Mar. 31, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Short Term Debt [Line Items]
Change in fair value of loans payable			$ (2,366)		$ (2,366)
Loans Payable | L A V Series A And Series B Promissory Note
Short Term Debt [Line Items]
Outstanding amount settlement from proceeds received from note receivable	$ 10,800
Series C convertible preferred stock | Loans Payable
Short Term Debt [Line Items]
Proceeds from promissory note receivable	$ 1,900
Other Expense
Short Term Debt [Line Items]
Change in fair value of loans payable						$ 2,900
PWERM Method
Short Term Debt [Line Items]
Probability of IPO in the near term potential outcome percentage through loans payable value approach, scenario one						60.00%
Probability of company remaining private potential outcome percentage through loans payable value approach, scenario two						40.00%
Company remaining private potential outcome through loans payable value approach, period						1 year 9 months

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Millions	1 Months Ended
	Dec. 31, 2020	May 31, 2020	Oct. 31, 2018	Apr. 30, 2017	Sep. 30, 2021	Feb. 28, 2021
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued upon conversion	16,079,230					16,079,230
Convertible preferred stock, shares issued	12,958,452				0
Convertible preferred stock, par value	$ 0.0001				$ 0.0001
Bridge Loan
Convertible Preferred Stock [Line Items]
Debt conversion to stock, aggregate debt plus accrued interest	$ 1.9
2020 Notes
Convertible Preferred Stock [Line Items]
Debt conversion to stock, aggregate debt plus accrued interest	$ 15.9
Series A convertible preferred stock
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued upon conversion	2,857,142
Convertible preferred stock, shares issued	2,857,142			2,089,285
Convertible preferred stock, par value				$ 10.50
Aggregate purchase price				$ 21.9
Series A convertible preferred stock | LAV Affiliate
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued	767,857
Series A convertible preferred stock | Terns China
Convertible Preferred Stock [Line Items]
Proceeds from sale of convertible preferred stock				$ 8
Series B convertible preferred stock
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued upon conversion	5,721,423
Convertible preferred stock, shares issued	2,600,645		2,384,195
Convertible preferred stock, par value			$ 30.80
Aggregate purchase price			$ 73.4
Series B convertible preferred stock | LAV Affiliate
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued	216,450
Series B convertible preferred stock | Terns China
Convertible Preferred Stock [Line Items]
Proceeds from sale of convertible preferred stock			$ 6.7
Series C convertible preferred stock
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued upon conversion	7,500,665
Convertible preferred stock, shares issued	7,500,665
Convertible preferred stock, par value	$ 11.65
Gross proceeds from issuance and conversion of convertible preferred stock	$ 87.4
Debt conversion, converted instrument, shares		1,366,820
Series C convertible preferred stock | Bridge Loan
Convertible Preferred Stock [Line Items]
Debt conversion, converted instrument, shares	167,159
Series C convertible preferred stock | 2020 Notes
Convertible Preferred Stock [Line Items]
Debt conversion, converted instrument, shares	1,366,820
IPO
Convertible Preferred Stock [Line Items]
Convertible preferred stock, shares issued upon conversion						16,079,230

Convertible Preferred Stock - S

Convertible Preferred Stock - Schedule of Convertible Preferred Stock (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Feb. 28, 2021	Dec. 31, 2020	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Dec. 31, 2019	Oct. 31, 2018	Apr. 30, 2017
Convertible Preferred Stock [Line Items]
Convertible Preferred Stock Authorized	10,000,000				188,029,084
Convertible Preferred Stock Issued	0				12,958,452
Convertible Preferred Stock Outstanding	0				12,958,452
Carrying Value					$ 186,033
Liquidation Preference					$ 197,468
Common Stock Issuable Upon Conversion				16,079,230	16,079,230
Series A convertible preferred stock
Convertible Preferred Stock [Line Items]
Convertible Preferred Stock Authorized					40,000,000
Convertible Preferred Stock Issued					2,857,142						2,089,285
Convertible Preferred Stock Outstanding	0	0	0		2,857,142	2,089,285	2,089,285	2,089,285	2,089,285
Carrying Value					$ 30,000
Liquidation Preference					$ 30,000
Common Stock Issuable Upon Conversion					2,857,142
Series B convertible preferred stock
Convertible Preferred Stock [Line Items]
Convertible Preferred Stock Authorized					36,409,088
Convertible Preferred Stock Issued					2,600,645					2,384,195
Convertible Preferred Stock Outstanding	0	0	0		2,600,645	2,384,195	2,384,195	2,384,195	2,384,195
Carrying Value					$ 68,995
Liquidation Preference					$ 80,100
Common Stock Issuable Upon Conversion					5,721,423
Series C convertible preferred stock
Convertible Preferred Stock [Line Items]
Convertible Preferred Stock Authorized					111,619,996
Convertible Preferred Stock Issued					7,500,665
Convertible Preferred Stock Outstanding	0	0	0		7,500,665	0	0	0
Carrying Value					$ 87,038
Liquidation Preference					$ 87,368
Common Stock Issuable Upon Conversion					7,500,665

Common Stock and Stock-Based _3

Common Stock and Stock-Based Compensation - Schedule of Common Stock Shares Reserved for Issuance (Details) - shares	Sep. 30, 2021	Dec. 31, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved	4,960,533	18,563,456
Conversion of Outstanding Shares of Convertible Preferred Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved		16,079,230
Options Outstanding Under Incentive Award Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved	3,556,043	2,466,670
Shares Available for Future Grant under Incentive Award Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved	1,164,490	17,556
Shares Available for Future Grant under Employee Stock Purchase Plans
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved	240,000

Common Stock and Stock-Based _4

Common Stock and Stock-Based Compensation - Additional Information (Details)	1 Months Ended	9 Months Ended
	Feb. 28, 2021shares	Sep. 30, 2021USD ($)PlanVoteshares	Dec. 31, 2020shares
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Common stock, voting rights		Each share of common stock entitles the holder to one vote on all matters submitted to a vote of the Company’s stockholders. Common stockholders are entitled to receive dividends
Number of voting rights per share | Vote		1
Cash dividends declared or paid | $		$ 0
Number of stock-based compensation plans | Plan		2
Share-based compensation, vesting period		4 years
Share-based compensation, expiration period		10 years
Total shares reserved		4,960,533	18,563,456
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense related to unvested stock options | $		$ 31,000,000
Unrecognized stock-based compensation expense recognized period		3 years 2 months 19 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense related to unvested stock options | $		$ 0
2021 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, number of shares authorized	2,400,007
Share-based payment award, shares available for future grants		1,164,490
2017 Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Share-based payment award, shares issued in period	0
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total shares reserved	240,000
Increase of authorized shares, percent of common stock outstanding	1.00%

Common Stock and Stock-Based _5

Common Stock and Stock-Based Compensation - Summary of Stock Option Activity (Details) - Stock Options $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2021USD ($)$ / sharesshares	Dec. 31, 2020USD ($)$ / sharesshares
Number of Shares
Number of Shares, Outstanding beginning balance | shares	2,466,670
Number of Shares, Granted | shares	1,383,480
Number of Shares, Exercised | shares	(151,678)
Number of Shares, Forfeited | shares	(142,429)
Number of Shares, Outstanding ending balance | shares	3,556,043	2,466,670
Number of Shares, Exercisable | shares	1,864,855
Number of Shares, Vested and expected to vest | shares	3,556,043
Weighted-Average Exercise Price
Weighted-Average Exercise Price, Outstanding beginning balance | $ / shares	$ 8.03
Weighted-Average Exercise Price, Granted | $ / shares	11.92
Weighted-Average Exercise Price, Exercised | $ / shares	5.92
Weighted-Average Exercise Price, Forfeited | $ / shares	7.25
Weighted-Average Exercise Price, Outstanding ending balance | $ / shares	9.75	$ 8.03
Weighted-Average Exercise Price, Exercisable | $ / shares	8.32
Weighted-Average Exercise Price, Vested and expected to vest | $ / shares	$ 9.75
Weighted-Average Remaining Contractual Term and Aggregate Intrinsic Value
Weighted-Average Remaining Contractual Term, Outstanding	9 years 3 months 25 days	9 years 7 months 9 days
Weighted-Average Remaining Contractual Term, Exercisable	8 years 11 months 8 days
Weighted-Average Remaining Contractual Term, Vested and expected to vest	9 years 3 months 25 days
Aggregate Intrinsic Value, Outstanding, beginning balance | $	$ 21,678
Aggregate Intrinsic Value, Exercised | $	831
Aggregate Intrinsic Value, Outstanding, ending balance | $	4,501	$ 21,678
Aggregate Intrinsic Value, Exercisable | $	3,923
Aggregate Intrinsic Value, Vested and expected to vest | $	$ 4,501

Common Stock and Stock-Based _6

Common Stock and Stock-Based Compensation - Schedule of Stock Options Weighted Average Assumptions (Details) - $ / shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Expected option life	6 years 10 days	6 years 7 days
Expected volatility	76.59%	61.96%
Risk-free interest rate	1.12%	0.43%
Expected dividend yield	0.00%	0.00%
Fair value of underlying common stock	$ 11.92	$ 20.72
Fair value of option	$ 7.87	$ 16.14

Common Stock and Stock-Based _7

Common Stock and Stock-Based Compensation - Summary of Restricted Stock Award Activity (Details) - Restricted Stock	9 Months Ended
	Sep. 30, 2021$ / sharesshares
Number of Shares
Number of Shares, Unvested restricted common stock, beginning balance | shares	83,334
Number of Shares, Vested | shares	(71,429)
Number of Shares, Forfeited | shares	(11,905)
Number of Shares, Unvested restricted common stock, ending balance | shares	0
Grant-Date Fair Value
Grant-Date Fair Value, Unvested restricted common stock, beginning balance | $ / shares	$ 1.96
Grant-Date Fair Value, Vested | $ / shares	1.96
Grant-Date Fair Value, Forfeited | $ / shares	1.96
Grant-Date Fair Value, Unvested restricted common stock, ending balance | $ / shares	$ 0

Common Stock and Stock-Based _8

Common Stock and Stock-Based Compensation - Schedule of Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,855	$ 513	$ 5,596	$ 905
Research and Development Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	401	84	1,374	228
General and Administrative Expense
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Total stock-based compensation expense	$ 1,454	$ 429	$ 4,222	$ 677

Income Tax - Additional Informa

Income Tax - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Income Taxes [Line Items]
Income Tax Provision (Benefit)	$ 20	$ 102	$ 73	$ 102
Foreign Tax Positions
Income Taxes [Line Items]
Income Tax Provision (Benefit)	$ 100	$ 100	$ 100	$ 100

Net Loss Per Common Share - Sch

Net Loss Per Common Share - Schedule of Computation of Basic and Diluted Net Loss per Common Share (Details) - USD ($) $ / shares in Units, $ in Thousands	3 Months Ended						9 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021	Sep. 30, 2020	Jun. 30, 2020	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Earnings Per Share [Abstract]
Net loss	$ (11,835)			$ (11,591)			$ (35,910)	$ (30,642)
Net loss attributable to non-controlling interest				(156)				(518)
Net loss attributable to common stockholders	$ (11,835)	$ (10,738)	$ (13,337)	$ (11,435)	$ (9,688)	$ (9,001)	$ (35,910)	$ (30,124)
Weighted average common stock outstanding, basic and diluted	25,148,336			302,336			21,842,706	270,463
Net loss per share attributable to common stockholders, basic and diluted	$ (0.47)			$ (37.82)			$ (1.64)	$ (111.38)

Net Loss Per Common Share - S_2

Net Loss Per Common Share - Schedule of Antidilutive Securities Excluded from Computation of Net Loss per Share (Details) - shares	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,556,043	9,342,192
Options to Purchase Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	3,556,043	940,034
Restricted Common Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	83,334
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	7,334,518
Options to Purchase Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Antidilutive securities excluded from computation of earnings per share	0	984,306

Commitments and Contingencies -

Commitments and Contingencies - Schedule of Future Minimum Lease Payments Due Under Operating Leases (Details) $ in Thousands	Sep. 30, 2021USD ($)
Leases [Abstract]
2021	$ 175
2022	675
2023	652
2024	559
2025 and thereafter	0
Total	$ 2,061

Assignment, License and Colla_2

Assignment, License and Collaboration Agreements - Additional Information (Details)	1 Months Ended				3 Months Ended		9 Months Ended		12 Months Ended
	Jul. 31, 2020USD ($)	Jun. 30, 2019CNY (¥)	Mar. 31, 2018USD ($)	Feb. 28, 2018USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)	Dec. 31, 2019USD ($)	Dec. 31, 2018USD ($)
TERN-101 License Agreement with Eli Lilly
Assignment License And Collaboration Agreements [Line Items]
Agreement milestones payment							$ 0
Research and development expense					$ 0	$ 0	0	$ 0
TERN-101 License Agreement with Eli Lilly | China
Assignment License And Collaboration Agreements [Line Items]
Aggregate pre-specified development milestones for the first covered product				$ 6,000,000
Aggregate pre-specified development milestones for the first covered product in ex-mainland				$ 50,000,000
TERN-201 License Agreement with Eli Lilly
Assignment License And Collaboration Agreements [Line Items]
Aggregate pre-specified development milestones for the first covered product			$ 74,000,000
Agreement milestones payment							0
Research and development expense					0	0	0	0
Aggregate pre-specified development milestones for second indication of covered product			$ 30,000,000
Amount paid under the agreement							4,000,000
TERN-201 License Agreement with Eli Lilly | Research and Development Expense
Assignment License And Collaboration Agreements [Line Items]
Upfront payment											$ 4,000,000
Assignment Agreement
Assignment License And Collaboration Agreements [Line Items]
Aggregate pre-specified development milestones for the first covered product | ¥		¥ 205,000,000
Research and development expense					$ 0	$ 0	0	$ 0
Amount paid under the agreement							$ 2,200,000
Number of days advance written notice							60 days
Milestone payment							$ 1,500,000
Assignment Agreement | Research and Development Expense
Assignment License And Collaboration Agreements [Line Items]
Upfront payment										$ 700,000
Hansoh Option and License Agreement
Assignment License And Collaboration Agreements [Line Items]
Refundable and non-creditable upfront payment	$ 1,000,000
Upfront payment refund period from expiration or termination of option	6 months
Percentage of interest rate on refund amount	5.00%
Upfront payment received									$ 800,000
Hansoh Option and License Agreement | Maximum
Assignment License And Collaboration Agreements [Line Items]
Amount agree to pay in pre-specified clinical, regulatory and sales milestones	$ 67,000,000