Sana Biotechnology (SANA) 10-Q 8 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	Sana Biotechnology, Inc.
Entity Central Index Key	0001770121
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Current Fiscal Year End Date	--12-31
Entity Filer Category	Non-accelerated Filer
Entity Common Stock, Shares Outstanding		188,832,954
Entity Shell Company	false
Entity Small Business	false
Entity Emerging Growth Company	true
Entity Ex Transition Period	false
Entity File Number	001-39941
Entity Tax Identification Number	83-1381173
Entity Address Address Line1	188 East Blaine Street
Entity Address, Address Line Two	Suite 400
Entity Address City Or Town	Seattle
Entity Address State Or Province	WA
Entity Address Postal Zip Code	98102
City Area Code	206
Local Phone Number	701-7914
Document Quarterly Report	true
Document Transition Report	false
Entity Incorporation State Country Code	DE
Title of 12(b) Security	Common Stock, $0.0001 par value
Trading Symbol	SANA
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	$ 433,670	$ 124,806
Marketable securities	170,041	253,458
Prepaid expenses and other current assets	9,134	6,203
Total current assets	612,845	384,467
Property and equipment, net	63,445	46,775
Operating lease right-of-use assets	84,828	63,168
Restricted cash	8,819	2,143
Long-term marketable securities	262,401	33,731
Intangible asset	59,195	59,195
Goodwill	140,627	140,627
Other non-current assets	591	190
TOTAL ASSETS	1,232,751	730,296
Current liabilities:
Accounts payable	3,947	2,253
Accrued compensation	20,218	16,020
Accrued expenses and other current liabilities	12,884	9,466
Operating lease liabilities	6,502	3,712
Contingent consideration	43,459
Success payment liabilities	5,000
Total current liabilities	92,010	31,451
Operating lease liabilities, net of current portion	92,403	68,197
Contingent consideration, net of current portion	88,522	121,901
Success payment liabilities, net of current portion	129,192	76,494
Other non-current liabilities	539	540
Total liabilities	402,666	298,583
Commitments and contingencies (Note 10)
Convertible preferred stock, $0.0001 par value; zero and 537,786 shares authorized as of September 30, 2021 and December 31, 2020, respectively; zero and 134,113 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively		852,897
Stockholders' equity (deficit):
Preferred stock, $0.0001 par value; 50,000 and zero shares authorized as of September 30, 2021 and December 31, 2020, respectively; zero shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively
Common stock, $0.0001 par value; 750,000 and 707,000 shares authorized as of September 30, 2021 and December 31, 2020, respectively; 182,908 and 16,170 shares issued and outstanding as of September 30, 2021 and December 31, 2020, respectively	18	2
Additional paid-in capital	1,504,778	8,216
Accumulated other comprehensive income (loss)	(82)	30
Accumulated deficit	(674,629)	(429,432)
Total stockholders' equity (deficit)	830,085	(421,184)
TOTAL LIABILITIES, CONVERTIBLE PREFERRED STOCK, AND STOCKHOLDERS' EQUITY (DEFICIT)	$ 1,232,751	$ 730,296

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, shares authorized	0	537,786,000
Convertible preferred stock, shares issued	0	134,113,000
Convertible preferred stock, shares outstanding	0	134,113,000
Preferred stock, par value	$ 0.0001	$ 0.0001
Preferred stock, shares authorized	50,000,000	0
Preferred stock, shares issued	0	0
Preferred stock, shares outstanding	0	0
Common stock, par value	$ 0.0001	$ 0.0001
Common stock, shares authorized	750,000,000	707,000,000
Common stock, shares issued	182,908,000	16,170,000
Common stock, shares outstanding	182,908,000	16,170,000

Condensed Consolidated Statemen

Condensed Consolidated Statements of Operations (Unaudited) - USD ($) shares in Thousands, $ 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	$ 53,245	$ 40,056	$ 140,121	$ 96,453
Research and development related success payments and contingent consideration	16,753	4,489	67,778	57,309
General and administrative	13,433	7,099	37,731	19,063
Total operating expenses	83,431	51,644	245,630	172,825
Loss from operations	(83,431)	(51,644)	(245,630)	(172,825)
Interest income, net	158	148	409	622
Other income, net	10	44	24	68
Net loss	$ (83,263)	$ (51,452)	$ (245,197)	$ (172,135)
Net loss per common share - basic and diluted	$ (0.46)	$ (3.76)	$ (1.53)	$ (14.05)
Weighted-average number of common shares - basic and diluted	181,827	13,680	160,515	12,249

Condensed Consolidated Statem_2

Condensed Consolidated Statements of Comprehensive Loss - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Statement Of Income And Comprehensive Income [Abstract]
Net loss	$ (83,263)	$ (51,452)	$ (245,197)	$ (172,135)
Other comprehensive income (loss), net of tax:
Unrealized gain (loss) on marketable securities, net	(95)	32	(112)	29
Total comprehensive loss	$ (83,358)	$ (51,420)	$ (245,309)	$ (172,106)

Condensed Consolidated Statem_3

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Unaudited) - USD ($) $ in Thousands	Total	IPO	Convertible Preferred Stock	Common Stock	Common StockIPO	Additional Paid-in Capital	Additional Paid-in CapitalIPO	Accumulated Other Comprehensive Income (Loss)	Accumulated Deficit
Beginning balance at Dec. 31, 2019	$ (142,542)			$ 1		$ 1,558		$ 26	$ (144,127)
Beginning balance (in shares) at Dec. 31, 2019			106,890,000
Beginning balance at Dec. 31, 2019			$ 417,359
Beginning balance (in shares) at Dec. 31, 2019				10,003,000
Vesting of restricted stock (in shares)				1,427,000
Exercise of stock options	2					2
Exercise of stock options (in shares)				2,000
Stock-based compensation expense	755					755
Unrealized gain (loss) on marketable securities, net	(10)							(10)
Net income (loss)	(32,875)								(32,875)
Ending balance at Mar. 31, 2020	(174,670)			$ 1		2,315		16	(177,002)
Ending balance (in shares) at Mar. 31, 2020			106,890,000
Ending balance at Mar. 31, 2020			$ 417,359
Ending balance (in shares) at Mar. 31, 2020				11,432,000
Beginning balance at Dec. 31, 2019	(142,542)			$ 1		1,558		26	(144,127)
Beginning balance (in shares) at Dec. 31, 2019			106,890,000
Beginning balance at Dec. 31, 2019			$ 417,359
Beginning balance (in shares) at Dec. 31, 2019				10,003,000
Net income (loss)	(172,135)
Ending balance at Sep. 30, 2020	(311,175)			$ 1		5,031		55	(316,262)
Ending balance (in shares) at Sep. 30, 2020			134,113,000
Ending balance at Sep. 30, 2020			$ 852,897
Ending balance (in shares) at Sep. 30, 2020				14,250,000
Beginning balance at Mar. 31, 2020	(174,670)			$ 1		2,315		16	(177,002)
Beginning balance (in shares) at Mar. 31, 2020			106,890,000
Beginning balance at Mar. 31, 2020			$ 417,359
Beginning balance (in shares) at Mar. 31, 2020				11,432,000
Issuance of Series B convertible preferred stock, net of issuance costs			$ 435,538
Issuance of Series B convertible preferred stock, net of issuance costs, (in shares)			27,223,000
Issuance of common stock in connection with license agreement	388					388
Issuance of common stock in connection with license agreement (in shares)				63,000
Vesting of restricted stock (in shares)				1,382,000
Exercise of stock options	35					35
Exercise of stock options (in shares)				24,000
Stock-based compensation expense	1,116					1,116
Unrealized gain (loss) on marketable securities, net	7							7
Net income (loss)	(87,808)								(87,808)
Ending balance at Jun. 30, 2020	(260,932)			$ 1		3,854		23	(264,810)
Ending balance (in shares) at Jun. 30, 2020			134,113,000
Ending balance at Jun. 30, 2020			$ 852,897
Ending balance (in shares) at Jun. 30, 2020				12,901,000
Vesting of restricted stock (in shares)				1,343,000
Exercise of stock options	9					9
Exercise of stock options (in shares)				6,000
Stock-based compensation expense	1,168					1,168
Unrealized gain (loss) on marketable securities, net	32							32
Net income (loss)	(51,452)								(51,452)
Ending balance at Sep. 30, 2020	(311,175)			$ 1		5,031		55	(316,262)
Ending balance (in shares) at Sep. 30, 2020			134,113,000
Ending balance at Sep. 30, 2020			$ 852,897
Ending balance (in shares) at Sep. 30, 2020				14,250,000
Beginning balance at Dec. 31, 2020	$ (421,184)			$ 2		8,216		30	(429,432)
Beginning balance (in shares) at Dec. 31, 2020	134,113,000		134,113,000
Beginning balance at Dec. 31, 2020	$ 852,897		$ 852,897
Beginning balance (in shares) at Dec. 31, 2020	16,170,000			16,170,000
Conversion of convertible preferred stock into common stock upon initial public offering	$ 852,897			$ 13		852,884
Conversion of convertible preferred stock into common stock, upon initial public offering (in shares)			(134,113,000)
Conversion of convertible preferred stock into common stock, upon initial public offering			$ (852,897)
Conversion of convertible preferred stock into common stock, upon initial public offering (in shares)				134,113,000
Issuance of common stock in initial public offering, net of offering costs		$ 626,405			$ 3		$ 626,402
Issuance of common stock in initial public offering, net of offering costs (in shares)					27,025,000
Vesting of restricted stock (in shares)				1,428,000
Exercise of stock options	298					298
Exercise of stock options (in shares)				205,000
Stock-based compensation expense	4,158					4,158
Unrealized gain (loss) on marketable securities, net	26							26
Net income (loss)	(180,617)								(180,617)
Ending balance at Mar. 31, 2021	881,983			$ 18		1,491,958		56	(610,049)
Ending balance (in shares) at Mar. 31, 2021				178,941,000
Beginning balance at Dec. 31, 2020	$ (421,184)			$ 2		8,216		30	(429,432)
Beginning balance (in shares) at Dec. 31, 2020	134,113,000		134,113,000
Beginning balance at Dec. 31, 2020	$ 852,897		$ 852,897
Beginning balance (in shares) at Dec. 31, 2020	16,170,000			16,170,000
Exercise of stock options (in shares)	1,121,000
Net income (loss)	$ (245,197)
Ending balance at Sep. 30, 2021	$ 830,085			$ 18		1,504,778		(82)	(674,629)
Ending balance (in shares) at Sep. 30, 2021	0		0
Ending balance (in shares) at Sep. 30, 2021	182,908,000			182,908,000
Beginning balance at Mar. 31, 2021	$ 881,983			$ 18		1,491,958		56	(610,049)
Beginning balance (in shares) at Mar. 31, 2021				178,941,000
Vesting of restricted stock (in shares)				1,423,000
Exercise of stock options	333					333
Exercise of stock options (in shares)				212,000
Stock-based compensation expense	4,941					4,941
Unrealized gain (loss) on marketable securities, net	(43)							(43)
Net income (loss)	18,683								18,683
Ending balance at Jun. 30, 2021	905,897			$ 18		1,497,232		13	(591,366)
Ending balance (in shares) at Jun. 30, 2021				180,576,000
Vesting of restricted stock (in shares)				1,628,000
Exercise of stock options	1,596					1,596
Exercise of stock options (in shares)				704,000
Stock-based compensation expense	5,950					5,950
Unrealized gain (loss) on marketable securities, net	(95)							(95)
Net income (loss)	(83,263)								(83,263)
Ending balance at Sep. 30, 2021	$ 830,085			$ 18		$ 1,504,778		$ (82)	$ (674,629)
Ending balance (in shares) at Sep. 30, 2021	0		0
Ending balance (in shares) at Sep. 30, 2021	182,908,000			182,908,000

Condensed Consolidated Statem_4

Condensed Consolidated Statements of Convertible Preferred Stock and Stockholders' Equity (Deficit) (Parenthetical) (Unaudited) - USD ($) $ in Thousands	3 Months Ended
	Mar. 31, 2021	Mar. 31, 2020
Series B Convertible Preferred Stock
Convertible preferred stock, issuance costs		$ 33
IPO
Issuance of common stock in initial public offering, net of offering costs	$ 49,220

Condensed Consolidated Statem_5

Condensed Consolidated Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
OPERATING ACTIVITIES:
Net loss			$ (245,197)	$ (172,135)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation	$ 2,800	$ 1,600	7,735	4,166
Stock-based compensation expense			15,049	3,037
Change in the estimated fair value of contingent consideration			10,080	16,672
Change in the estimated fair value of success payment liabilities			57,698	40,637
Non-cash expense for operating lease right-of-use assets			4,597	2,889
Other non-cash items, net			(2,255)	819
Changes in operating assets and liabilities:
Prepaid expenses and other assets			(2,985)	682
Operating lease right-of-use assets and liabilities			5,028	91
Accounts payable			1,397	2,414
Accrued expenses and other liabilities			7,898	305
Net cash used in operating activities			(140,955)	(100,423)
INVESTING ACTIVITIES:
Purchases of marketable securities			(414,437)	(307,398)
Proceeds from sales and maturities of marketable securities			266,960	56,400
Purchases of property and equipment			(24,660)	(14,606)
Net cash used in investing activities			(172,137)	(265,604)
FINANCING ACTIVITIES:
Proceeds from initial public offering of common stock, net of offering costs			626,405
Proceeds from issuance of convertible preferred stock, net of issuance costs				435,538
Proceeds from exercise of stock options			2,227	46
Net cash provided by financing activities			628,632	435,584
Net increase in cash, cash equivalents, and restricted cash			315,540	69,557
Cash, cash equivalents, and restricted cash at beginning of period			126,949	81,807	$ 81,807
Cash, cash equivalents, and restricted cash at end of period	$ 442,489	$ 151,364	442,489	151,364	$ 126,949
SUPPLEMENTAL CASH FLOW DISCLOSURES:
Right-of-use assets obtained in exchange for operating lease liabilities			26,257	23,049
Cash received from lessor for tenant improvement allowance			5,160	91
Tenant improvement allowance included in operating lease liabilities			4,438	8,515
Purchases of property and equipment included in accounts payable and accrued liabilities			$ 3,231	$ 4,238

Organization

Organization	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Organization	1. Organization Sana Biotechnology, Inc. (the Company or Sana) was incorporated in Delaware on July 13, 2018 (inception) as FD Therapeutics, Inc., and changed its name to Sana Biotechnology, Inc. on September 17, 2018. Sana is a biotechnology company focusing on utilizing engineered cells as medicines. The Company’s operations to date have included identifying and developing potential product candidates, executing preclinical studies, establishing manufacturing capabilities, acquiring technology, organizing and staffing the Company, business planning, establishing the Company’s intellectual property portfolio, raising capital, and providing general and administrative support for these operations. Reverse stock split In January 2021, the Company’s board of directors approved an amendment to the Company’s amended and restated certificate of incorporation to effect a 1-for-4 Initial public offering In February 2021, the Company successfully completed its initial public offering (IPO) of its common stock. In connection with its IPO, the Company issued 27.0 million shares of its common stock, including 3.5 million shares pursuant to the full exercise of the underwriters’ option to purchase additional shares, at a price of $25.00 per share, and received $626.4 million in net proceeds, after deducting underwriting discounts and commissions of $45.2 million and offering expenses of $4.0 million. At the closing of the IPO, 134.1 million shares of convertible preferred stock then outstanding were automatically converted into shares of common stock. The related carrying value of the converted preferred stock of $852.9 million was reclassified to common stock and additional paid in-capital. Need for additional capital The Company is subject to a number of risks and uncertainties similar to other biotechnology companies in the development stage, including, but not limited to, the need to obtain adequate additional funding, possible failure of preclinical testing or clinical trials, the need to obtain marketing approval for its product candidates, building out internal and external manufacturing capabilities, competitors developing new technological innovations, the need to successfully commercialize and gain market acceptance of the Company’s products, the need to protect the Company’s intellectual property and proprietary technology, and the need to attract and retain key scientific and management personnel. If the Company does not successfully commercialize or partner any of its product candidates, it will be unable to generate product revenue or achieve profitability. Until such time as the Company can generate significant revenue from product sales, if ever, it expects to finance its operations from additional equity or debt financings or other capital obtained in connection with strategic collaborations or licensing or other arrangements. In the event that additional financing is required, the Company may not be able to raise it on terms acceptable to it or at all. The Company has incurred operating losses each year since inception and expects such losses to continue for the foreseeable future. As of September 30, 2021, the Company had cash, cash equivalents, and marketable securities of $866.1 million, and an accumulated deficit of $674.6 million, which includes non-cash charges of $131.8 million and $80.7 million related to the revaluation of the success payment liabilities and contingent consideration, respectively.

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	2. Summary of significant accounting policies The accompanying condensed consolidated financial statements and related financial information should be read in conjunction with the audited consolidated financial statements and the related notes thereto included in the Company’s Annual Report on Form 10-K for the year ended December 31, 2020 filed with the SEC on March 24, 2021 (2020 Form 10-K). The significant accounting policies used in the preparation of these condensed consolidated financial statements as of September 30, 2021 and for the three and nine months ended September 30, 2021 and 2020 are consistent with those discussed in Note 2 in the 2020 Form 10-K. Basis of presentation The accompanying condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. The Company’s condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (GAAP). Certain prior period amounts have been reclassified to conform to current period presentation. Use of estimates The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates. The most significant estimates in the Company’s condensed consolidated financial statements relate to success payment liabilities, contingent consideration, business combinations, accrued expenses, and the valuation of stock options. Recent accounting pronouncements Recently adopted Accounting Standards Updates (ASU) No. 2016-13, Financial Instruments—Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements, ASU No. 2019-05 Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief, ASU No. 2019-11, Codification Improvements to Topic 326, Financial Instruments—Credit Losses In June 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements (ASU 2016-13). The new standard requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. It also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which the carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. The targeted transition relief standard allows companies an option to irrevocably elect the fair value option of ASC 825-10, Financial Instruments-Overall, applied on an instrument-by-instrument basis for eligible instruments. The Company adopted ASU 2016-13 effective January 1, 2021. The adoption of the guidance did not have a material impact on the condensed consolidated financial statements and related disclosures, and there was no allowance for losses on available-for-sale debt securities attributable to credit risk for the three and nine months ended September 30, 2021. Not yet adopted ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). To address concerns over the cost and complexity of the two-step goodwill impairment test, the amendments in this ASU remove the second step of the test. An entity will instead apply a one-step quantitative test and record the amount of goodwill impairment as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The new guidance does not amend the optional qualitative assessment of goodwill impairment. The new standard will be effective beginning January 1, 2023. The adoption of ASU 2017-04 is not expected to have a material impact on the Company’s consolidated financial statements.

Acquisitions

Acquisitions	9 Months Ended
	Sep. 30, 2021
Business Combinations [Abstract]
Acquisitions	3. Acquisitions Oscine Corp. In September 2020, the Company entered into a stock purchase agreement to acquire 100% of the outstanding equity in Oscine Corp. (Oscine) for a purchase price of $8.5 million, of which $7.6 million was an upfront cash payment and $0.9 million was set aside to satisfy certain general representations and warranties as set forth in the stock purchase agreement (Oscine Holdback Amount). The primary asset acquired in the acquisition was in-process research and development (IPR&D) technology related to Oscine’s glial progenitor ex vivo Business Combinations The Oscine Holdback Amount will be held until December 2021, which is 15 months following the consummation of the acquisition, at which time the remainder of the balance, after payment of any claims, will be released. In addition, the Company is required to make up to an aggregate of $225.8 million in future milestone payments upon the achievement of certain development and commercial milestones. Cobalt Biomedicine, Inc. In February 2019, the Company acquired 100% of the outstanding equity in Cobalt Biomedicine, Inc. (Cobalt), a privately-held early-stage biotechnology company that was developing a platform technology using its fusogen technology to specifically and consistently deliver various biological payloads to cells. Pursuant to the terms and conditions in the Cobalt acquisition agreement, the Company has an obligation to pay contingent consideration (Cobalt Contingent Consideration) of up to an aggregate of $500.0 million to certain former Cobalt stockholders upon the achievement of certain pre-specified development milestones. Additionally, the Company is obligated to pay a success payment (Cobalt Success Payment) of up to $500.0 million, payable in cash or stock, at the Company’s discretion. The Cobalt Success Payment is payable if, at pre-determined valuation measurement dates, including the Company’s IPO and periodically thereafter, the Company’s market capitalization equals or exceeds $8.1 billion, and the Company is advancing a program based on the fusogen technology in a clinical trial pursuant to an investigational new drug application (IND), or has filed for, or received approval for, a biologics license application (BLA) or new drug application (NDA). The Cobalt Success Payment can be achieved over a maximum of 20 years from the date of the Cobalt acquisition, but this period could be shorter upon the occurrence of certain events. As of September 30, 2021, a Cobalt Success Payment had not been triggered. In addition to an IPO, a valuation measurement date would be triggered upon a change of control of the Company if at least one Company product based on the fusogen technology is the subject of an active research program at the time of such change of control. If there is a change of control and the Company’s market capitalization is below $8.1 billion as of the date of the change of control, the amount of the potential Cobalt Success Payment will decrease, and the amount of potential Cobalt Contingent Consideration will increase. The following table sets forth various thresholds for the Company’s market capitalizations as of the date of a change of control and the resulting potential Cobalt Success Payment and additional potential Cobalt Contingent Consideration: Sana market capitalization upon a change of control and resulting impact to Cobalt Success Payment and additional potential Cobalt Contingent Consideration Cobalt Success Payment Additional potential Cobalt Contingent Consideration (in millions) Equal to or exceeds $8.1 billion $ 500 $ - Equal to or exceeds $7.4 billion, but less than $8.1 billion 150 350 Equal to or exceeds $6.8 billion, but less than $7.4 billion 100 400 Less than $6.8 billion - 500 The Cobalt Success Payment and Cobalt Contingent Consideration liabilities are carried at fair value, with changes in fair value recognized in the condensed consolidated statements of operations in research and development related success payments and contingent consideration. As of September 30, 2021 and December 31, 2020, the estimated fair value of the Cobalt Success Payment liability was $111.6 million and $64.7 million, respectively, and was recorded in long-term liabilities in the condensed consolidated balance sheets. In connection with the change in the estimated fair value of the Cobalt Success Payment, the Company recognized expenses of $21.8 million and $1.3 million for the three months ended September 30, 2021 and 2020, respectively, and expenses of $46.9 million and $35.2 million for the nine months ended September 30, 2021 and 2020, respectively. As of September 30, 2021, the estimated fair value of the Cobalt Contingent Consideration was $132.0 million, of which $43.5 million was recorded in short-term liabilities and $88.5 million was recorded in long-term liabilities in the condensed consolidated balance sheet. As of December 31, 2020, the estimated fair value of the Cobalt Contingent Consideration was $121.9 million and was recorded in long-term liabilities in the condensed consolidated balance sheet. In connection with the change in the estimated fair value of the Cobalt Contingent Consideration, we recognized a gain of $8.5 million and an expense of $2.3 million for the three months ended September 30, 2021 and 2020, respectively, and expenses of $10.1 million and $16.7 million for the nine months ended September 30, 2021 and 2020, respectively.

Intangible Asset and Goodwill

Intangible Asset and Goodwill	9 Months Ended
	Sep. 30, 2021
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible asset and goodwill	4. Intangible asset and goodwill As of September 30, 2021, the Company had an intangible asset of $59.2 million, which consists of IPR&D acquired in 2019 from the Cobalt acquisition. The IPR&D is classified as indefinite-lived until the successful completion of the associated research and development technology, at which point it becomes a finite-lived asset that will be amortized over its estimated useful life. As of September 30, 2021, there was no amortization of the intangible asset. As of September 30, 2021, the Company had goodwill of $140.6 million, which represents the excess of the purchase price over the estimated fair value of the net assets acquired from the Cobalt acquisition in 2019. There were no impairments of the intangible asset or goodwill since the acquisition.

License and collaboration agree

License and collaboration agreements	9 Months Ended
	Sep. 30, 2021
License And Collaboration Agreements [Abstract]
License and Collaboration Agreements	5. License and collaboration agreements President and Fellows of Harvard College In March 2019, the Company entered into an exclusive license agreement with the President and Fellows of Harvard College (Harvard) to access certain intellectual property for the development of hypo-immune cells. Under the terms of the agreement, the Company may be required to make success payments to Harvard up to an aggregate of $175.0 million, payable in cash, based on increases in the fair value of the Company’s common stock (Harvard Success Payments). The potential Harvard Success Payments are based on multiples of increased value ranging from 5x to 40x, based on a comparison of the fair market value of the Company’s common stock relative to the original issuance price of $4.00 per share at pre-determined valuation measurement dates which include: the one year anniversary of the IPO and periodically thereafter, the date of the consummation of a merger, an asset sale, or the sale of the majority of the shares held by the Company’s Series A convertible preferred stockholders, and the last day of the term of the Harvard Success Payments. The first Harvard valuation measurement date is expected to occur in February 2022, one year from the IPO. The aggregate amount of the Harvard Success Payments does not exceed an aggregate of $175.0 million, which would only occur upon a 40x increase in the fair value of the Company’s common stock. If a higher success payment tier is first met at the same time a lower tier is first met, both tiers will be owed. Any previous success payments made to Harvard would be credited against the success payment owed as of any valuation measurement date so that Harvard does not receive multiple success payments in connection with the same threshold. The Harvard Success Payments can be achieved over a maximum of 12 years from the effective date of the agreement. The following table summarizes the potential success payments and common stock price required for payment: Multiple of Equity Value at Issuance 5x 10x 20x 30x 40x Per share common stock price required for payment $ 20.00 $ 40.00 $ 80.00 $ 120.00 $ 160.00 Success payment(s) (in millions) $ 5.0 $ 15.0 $ 30.0 $ 50.0 $ 75.0 The Harvard Success Payment liabilities are carried at fair value, with changes in fair value recognized on the condensed consolidated statements of operations in research and development related success payments and contingent consideration. As of September 30, 2021 and December 31, 2020, the estimated fair value of the Harvard Success Payment liability was $22.6 million and $11.8 million, respectively. As of September 30, 2021 and December 31, 2020, $5.0 million and $0, respectively, were recorded in short-term liabilities, and $17.6 million and $11.8 million, respectively, were recorded in long-term liabilities in the condensed consolidated balance sheet. For the three months ended September 30, 2021 and 2020, the Company recognized expenses of $3.4 million and $0.8 million, respectively, in connection with the change in the estimated fair value of the Harvard Success Payment liability. For the nine months ended September 30, 2021 and 2020, the Company recognized expenses of $10.8 million and $5.5 million, respectively, in connection with the change in the estimated fair value of the Harvard Success Payment liability. In connection with this agreement, the Company also paid Harvard a license payment of $6.0 million in June 2020 that was contingent upon the closing of the Company’s Series B convertible preferred stock financing.

Restricted Cash

Restricted Cash	9 Months Ended
	Sep. 30, 2021
Restricted Cash And Cash Equivalents [Abstract]
Restricted Cash	6. Restricted cash As of September 30, 2021 and December 31, 2020, the Company maintained standby letters of credit of $8.8 million and $2.1 million, respectively, which are collateralized with a bank account at a financial institution in accordance with the applicable lease agreements.

Fair Value Measurements

Fair Value Measurements	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value Measurements	7. Fair value measurements The following tables summarize the Company’s financial assets and liabilities measured at fair value on a recurring basis based on the three-tier fair value hierarchy: September 30, 2021 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value (in thousands) Financial assets: Cash equivalents: Money market funds Level 1 $ 379,336 $ - $ - $ 379,336 Corporate debt securities Level 2 121 - - 121 Total cash equivalents 379,457 - - 379,457 Short-term marketable securities: U.S. government and agency securities Level 2 76,538 18 - 76,556 Corporate debt securities Level 2 93,504 4 (23 ) 93,485 Total short-term marketable securities 170,042 22 (23 ) 170,041 Long-term marketable securities: U.S. government and agency securities Level 2 226,861 24 (81 ) 226,804 Corporate debt securities Level 2 35,621 - (24 ) 35,597 Total long-term marketable securities 262,482 24 (105 ) 262,401 Total financial assets $ 811,981 $ 46 $ (128 ) $ 811,899 Financial liabilities: Short-term financial liabilities: Contingent consideration Level 3 $ 43,459 $ - $ - $ 43,459 Success payment liabilities Level 3 5,000 - - 5,000 Total short-term financial liabilities 48,459 - - 48,459 Long-term financial liabilities: Contingent consideration Level 3 88,522 - - 88,522 Success payment liabilities Level 3 129,192 - - 129,192 Total long-term financial liabilities 217,714 - - 217,714 Total financial liabilities $ 266,173 $ - $ - $ 266,173 December 31, 2020 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value (in thousands) Financial assets: Cash equivalents: Money market funds Level 1 $ 48,359 $ - $ - $ 48,359 U.S. government and agency securities Level 2 40,727 1 (1 ) 40,727 Corporate debt securities Level 2 1,138 - - 1,138 Total cash equivalents 90,224 1 (1 ) 90,224 Short-term marketable securities: U.S. government and agency securities Level 2 244,637 30 (5 ) 244,662 Corporate debt securities Level 2 8,798 - (2 ) 8,796 Total short-term marketable securities 253,435 30 (7 ) 253,458 Long-term marketable securities: U.S. government and agency securities Level 2 33,724 7 - 33,731 Total long-term marketable securities 33,724 7 - 33,731 Total financial assets $ 377,383 $ 38 $ (8 ) $ 377,413 Financial liabilities: Long-term financial liabilities: Contingent consideration Level 3 $ 121,901 $ - $ - $ 121,901 Success payment liabilities Level 3 76,494 - - 76,494 Total financial liabilities $ 198,395 $ - $ - $ 198,395 The Company measures the fair value of money market funds based on quoted prices in active markets for identical assets or liabilities. The Level 2 marketable securities include U.S. government, agency securities, and corporate debt securities and are valued based on either recent trades of securities in inactive markets or quoted market prices of similar instruments and other significant inputs derived from or corroborated by observable market data. Securities in an unrealized loss position have been in an unrealized loss position for less than one year. The Company determined that there was no material change in the credit risk of the above investments during the nine months ended September 30, 2021. As such, an allowance for credit losses has not been recognized. As of September 30, 2021, the Company does not intend to sell such securities, and it is not more-likely-than-not that the Company will be required to sell the securities prior to the recovery of the amortized cost basis. As of September 30, 2021, all marketable securities had an effective maturity date of two years or less. Investments in securities with maturities of less than one year, or those for which management intends to use to fund current operations, are included in current assets and classified as available-for-sale. As of September 30, 2021, the balance in accumulated other comprehensive income (loss) included the net unrealized gains (losses) related to the Company’s available-for-sale debt securities. There were no material realized gains or losses recognized on the sale or maturity of available-for-sale securities during the three and nine months ended September 30, 2021 or 2020. The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities: Contingent Consideration Cobalt Success Payment Liability Harvard Success Payment Liability (in thousands) Balance as of December 31, 2020 $ 121,901 $ 64,694 $ 11,800 Changes in fair value - expense (gain) 11,393 91,757 23,900 Balance as of March 31, 2021 133,294 156,451 35,700 Changes in fair value - expense (gain) 7,163 (66,632 ) (16,556 ) Balance as of June 30, 2021 140,457 89,819 19,144 Changes in fair value - expense (gain) (8,476 ) 21,790 3,439 Balance as of September 30, 2021 $ 131,981 $ 111,609 $ 22,583 Contingent consideration The Company utilizes significant estimates and assumptions it believes would be made by a market participant in determining the estimated fair value of the Cobalt Contingent Consideration at each balance sheet date. The fair value of the Cobalt Contingent Consideration was determined by calculating the probability-weighted estimated value of the pre-specified development milestone payments based on the assessment of the likelihood and estimated timing that the milestones would be achieved and the applicable discount rates. The discount rate captures the credit risk associated with the payment of the contingent consideration when earned and due. The Company assesses these estimates on an on-going basis as additional data impacting the assumptions are obtained. The fair value of the Cobalt Contingent Consideration was calculated using the following unobservable inputs: September 30, 2021 December 31, 2020 Unobservable Input Range Weighted-Average Range Weighted-Average Discount rates 10.8% - 11.6% 11.1% 10.5% - 10.8% 10.6% Probability of milestone achievement 5.0% - 65.0% 27.9% 2.5% - 65.0% 27.6% The weighted-average unobservable inputs were calculated based on the relative value of the pre-specified development milestones. The estimated fair value of the Cobalt Contingent Consideration may change significantly as development progresses and additional data are obtained, impacting the assumptions regarding probabilities of successful achievement of the milestones used to estimate the fair value of the liability and the timing in which they are expected to be achieved. In evaluating the fair value assumptions, judgment is required to interpret the market data used to develop the estimates. The estimates of fair value may not be indicative of the amounts that could be realized in a current market exchange. Accordingly, the use of different market assumptions, inputs and/or different valuation techniques could result in materially different fair value estimates. Success payments The Company utilizes significant estimates and assumptions in determining the estimated fair value of the success payment liabilities and the associated expense or gain at each balance sheet date. The estimated fair value of the Cobalt and Harvard success payment liabilities was determined using a Monte Carlo simulation methodology, which models the estimated fair value of the liability based on several key assumptions, including: the expected volatility, remaining term, risk-free interest rate, estimated number and timing of valuation measurement dates on the basis of which payment may be triggered, and for the Cobalt Success Payment, the Company’s market capitalization, and for the Harvard Success Payments, the per share fair value of the Company’s common stock. The fair values of the Cobalt and Harvard success payment liabilities were calculated using the following unobservable inputs: September 30, 2021 December 31, 2020 Unobservable Input Cobalt Harvard Cobalt Harvard Expected stock price volatility 70% 70% 70% 70% Expected term (years) 17.4 9.5 18.1 10.2

Property and Equipment, Net

Property and Equipment, Net	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Property and Equipment, Net	8. Property and equipment, net Property and equipment, net consists of the following: September 30, 2021 December 31, 2020 (in thousands) Laboratory equipment $ 41,585 $ 26,958 Leasehold improvements 26,109 15,598 Construction in progress 10,293 11,180 Computer equipment, software, and other 930 776 Total property and equipment, at cost 78,917 54,512 Less: Accumulated depreciation (15,472 ) (7,737 ) Property and equipment, net $ 63,445 $ 46,775 Depreciation expense was $2.8 million and $1.6 million for the three months ended September 30, 2021 and 2020, respectively, and $7.7 million and $4.2 million for the nine months ended September 30, 2021 and 2020, respectively.

Accrued Liabilities

Accrued Liabilities	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Accrued liabilities	9. Accrued liabilities Accrued compensation and accrued expenses and other current liabilities consist of the following: September 30, 2021 December 31, 2020 (in thousands) Accrued compensation: Accrued bonuses $ 9,670 $ 11,582 Accrued payroll 5,543 1,660 Accrued paid time off 4,981 2,441 Other accrued compensation 24 337 Total accrued compensation $ 20,218 $ 16,020 Accrued expenses and other current liabilities: Accrued research and development $ 4,358 $ 1,197 Accrued property and equipment 3,178 2,892 Accrued professional fees 2,209 1,717 Other accrued current liabilities 3,139 3,660 Total accrued expenses and other current liabilities $ 12,884 $ 9,466

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Commitments and Contingencies	10. Commitments and contingencies Lease commitments The Company’s lease portfolio is primarily comprised of operating leases for office, laboratory, non-good manufacturing practices (GMP) pilot plant manufacturing, and industrial space located in Seattle, WA, Cambridge, MA, South San Francisco, CA and Fremont, CA. Operating leases have contractual periods expiring between April 2024 and November 2031. These leases contain various rent abatement periods, after which they require monthly lease payments that may be subject to annual increases throughout the lease term. The Seattle and South San Francisco lease agreements each provide the Company with the option to renew for an additional period of five years. The Company is not reasonably certain it will renew these leases, and therefore the renewal options are not considered in the remaining lease term for these leases. The industrial space located in Fremont, CA will be used for the construction of a GMP manufacturing facility. The lease agreement initial term is ten years and includes the option to extend for up to two additional five-year The following table contains additional information related to our operating leases: Location Approximate Square Footage Commencement Dates Expiration Dates Seattle, WA 48,086 March 2019 to September 2020 December 2026 to April 2028 Cambridge, MA 56,859 March 2019 to May 2020 November 2025 to February 2028 South San Francisco, CA 66,075 December 2019 to September 2021 April 2024 to April 2030 Fremont, CA 163,193 July 2021 November 2031 Throughout the term of the lease agreements, the Company is responsible for paying certain operating costs in addition to rent, such as common area maintenance, taxes, utilities, and insurance. These additional charges are considered variable lease costs and are recognized in the period in which the costs are incurred. The following table summarizes the Company’s lease costs: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Operating lease cost $ 4,303 $ 2,750 $ 11,368 $ 7,870 Short-term lease cost - 474 512 1,418 Variable lease cost 1,286 837 4,015 2,306 Total lease cost $ 5,589 $ 4,061 $ 15,895 $ 11,594 As of September 30, 2021, the weighted-average remaining lease term was 7.9 years and the weighted-average incremental borrowing rate was 9.55%. The following table reconciles the Company’s undiscounted operating lease cash flows by fiscal year, to the present value of the operating lease liabilities as of September 30, 2021 (in thousands): 2021 (remaining 3 months) $ 2,867 2022 17,511 2023 17,677 2024 17,036 2025 17,151 2026 and thereafter 98,614 Total undiscounted lease payments 170,856 Less: imputed interest (67,513 ) Less: tenant improvement allowances (4,438 ) Present value of operating lease liabilities $ 98,905

Convertible Preferred Stock

Convertible Preferred Stock	9 Months Ended
	Sep. 30, 2021
Stockholders Equity Note [Abstract]
Convertible preferred stock	11. Convertible preferred stock In 2018, the Company issued 11.5 million shares of its Series A-1 convertible preferred stock at $4.00 per share, for gross proceeds of $45.9 million. In 2019, the Company issued 56.0 million shares of its Series A-2 convertible preferred stock at $4.00 per share, for gross proceeds of $224.0 million. In 2020, the Company issued 27.2 million shares of Series B convertible preferred stock at $16.00 per share, for gross proceeds of $435.6 million. Immediately prior to the closing of the Company’s IPO in February 2021, all outstanding shares of convertible preferred stock converted into 134.1 million shares of common stock. There were no shares of convertible preferred stock outstanding as of September 30, 2021.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	12. Stockholders’ equity The Company amended and restated its certificate of incorporation, effective February 2021, increasing the number of shares of all classes of stock the Company has authority to issue to 800.0 million shares, of which 750.0 million shares are common stock, and 50.0 million shares are preferred stock. As of September 30, 2021, there were 182.9 million shares of the Company’s common stock outstanding, excluding 5.8 million shares of restricted common stock outstanding that are subject to vesting requirements.

Stock-Based Compensation

Stock-Based Compensation	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Stock-based compensation	13. Stock-based compensation 2021 Incentive Award Plan In February 2021, the Company adopted the 2021 Incentive Award Plan, which became effective on the completion of the Company’s IPO. The 2021 Incentive Award Plan provides for a variety of stock-based compensation awards, including stock options, restricted stock awards (RSAs), and restricted stock units (RSUs). In conjunction with adopting the 2021 Incentive Award Plan, the Company discontinued the 2018 Equity Incentive Plan with respect to new equity awards. The number of shares of the Company’s common stock reserved for issuance is subject to automatically increase by 5% of all shares outstanding at the beginning of each calendar year. 2021 Employee Stock Purchase Plan In February 2021, the Company adopted the 2021 Employee Stock Purchase Plan (2021 ESPP), which became effective on the completion of the Company’s IPO. The 2021 ESPP allows eligible employees to purchase shares of the Company’s common stock at a discount through payroll deductions of up to 15% of their earnings, subject to plan limitations. Unless otherwise determined by the Company’s board of directors, employees are able to purchase shares at 85% of the lower of the fair market value of the Company’s common stock on the first date of an offering or on the purchase date. The number of shares of the Company’s common stock reserved for issuance under the 2021 ESPP is subject to automatically increase by 1% of all shares outstanding at the beginning of each calendar year. The Company may specify offerings with durations of not more than 27 months and may specify shorter purchase periods within each offering. 2018 Equity Incentive Plan In October 2018, the Company adopted the 2018 Equity Incentive Plan (2018 Plan), under which it may grant incentive stock options, non-statutory stock options, RSAs, RSUs, and other stock-based awards to any person, including officers, directors, and consultants. Terms of stock agreements, including vesting requirements, are determined by the Company’s board of directors, or by a committee appointed by the board of directors, subject to the provisions of the 2018 Plan. The 2018 Plan terminated as of the adoption of the 2021 Incentive Award Plan. Stock-based compensation expense Stock-based compensation expense is recognized in the condensed consolidated statements of operations as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Research and development $ 4,072 $ 980 $ 9,888 $ 2,555 General and administrative 1,878 186 5,161 482 Total stock-based compensation expense $ 5,950 $ 1,166 $ 15,049 $ 3,037 Unrecognized stock-based compensation costs related to unvested awards and the weighted-average period over which the costs are expected to be recognized as of September 30, 2021 are as follows: Stock Options RSAs RSUs Unrecognized stock-based compensation expense (in thousands) $ 79,637 $ 2,166 $ 887 Weighted-average period costs expected to be recognized (years) 2.8 1.1 1.5 Stock options A summary of the Company’s stock option activity is as follows: Stock Options (in thousands) Weighted- Average Exercise Price per Share Weighted-Average Remaining Contractual Life (years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 15,677 $ 4.52 Granted 3,398 23.26 Exercised (1,121 ) 1.99 Forfeited/Cancelled (671 ) 5.05 Outstanding as of September 30, 2021 17,283 $ 8.34 8.9 $ 244,590 Exercisable as of September 30, 2021 2,874 $ 2.05 8.2 $ 58,832 The fair value of stock options granted to employees, directors, and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following assumptions: Nine Months Ended September 30, Assumptions 2021 2020 Risk free interest rate 0.46% - 1.15% 0.36% - 1.51% Expected volatility 70 % 70 % Expected term (years) 5.50 - 6.40 6.25 - 6.75 Expected dividend 0 % 0 % The following table summarizes additional information related to stock option activity: Nine Months Ended September 30, 2021 2020 Weighted average grant date fair value per share for options granted $ 14.64 $ 0.54 Aggregate intrinsic value of stock options exercised (in thousands) $ 22,187 $ 205 Restricted stock awards A summary of the Company’s RSA activity is as follows: RSAs (in thousands) Weighted-Average Grant Date Fair Value per Share Unvested shares as of December 31, 2020 10,079 $ 0.33 Vested (4,273 ) 0.25 Forfeited (15 ) 0.73 Unvested shares as of September 30, 2021 5,791 $ 0.39 The fair value of vested RSAs for the three months ended September 30, 2021 and 2020 was $0.4 million and $0.2 million, respectively, and $1.1 million and $0.6 million for the nine months ended September 30, 2021 and 2020, respectively. As of December 31, 2020, there were 0.3 million RSUs unvested. During the nine months ended September 30, 2021 there were 0.1 million granted, 0.2 million vested. As of September 30, 2021, there are 0.2 million RSUs unvested.

Income Taxes

Income Taxes	9 Months Ended
	Sep. 30, 2021
Income Tax Disclosure [Abstract]
Income Taxes	14. Income taxes The Company’s income tax provision for interim periods is determined using an estimate of the Company’s annual effective tax rate, adjusted for discrete items arising in the quarter. The Company’s effective tax rate differs from the U.S. statutory tax rate primarily due to a valuation allowance on the deferred tax assets. Deferred tax assets and deferred tax liabilities are recognized based on temporary differences between the financial reporting and tax basis of assets and liabilities using statutory rates. A valuation allowance is recorded against deferred tax assets if it is more likely than not that some or all of the deferred tax assets will not be realized. Due to the uncertainty surrounding the realization of the favorable tax attributes in future tax returns, the Company has recorded a full valuation allowance against the Company’s otherwise recognizable net deferred tax assets.

Net Loss Per Share

Net Loss Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Loss Per Share	15. Net loss per share Basic and diluted net loss per common share is calculated by dividing net loss by the weighted-average number of common shares outstanding during the period, without consideration for common stock equivalents. The Company was in a loss position for all periods presented; therefore, basic net loss per share and diluted net loss per share are the same for all periods, as the inclusion of all potential common securities outstanding would have been anti-dilutive. The following table summarizes the calculation of basic and diluted net loss per share of common stock: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands, except per share amounts) Net loss $ (83,263 ) $ (51,452 ) $ (245,197 ) $ (172,135 ) Weighted-average number of common shares - basic and diluted 181,827 13,680 160,515 12,249 Net loss per common share - basic and diluted $ (0.46 ) $ (3.76 ) $ (1.53 ) $ (14.05 ) The following securities were excluded from the computation of net loss per diluted share of common stock for periods presented as their effect would have been anti-dilutive: Nine Months Ended September 30, 2021 2020 (in thousands) Convertible preferred stock - 134,113 Options issued and outstanding 17,284 9,677 Unvested restricted common stock 5,791 11,952 Unvested RSUs 150 326 Total 23,225 156,068

Employee Benefit Plan

Employee Benefit Plan	9 Months Ended
	Sep. 30, 2021
Compensation And Retirement Disclosure [Abstract]
Employee Benefit Plan	16. Employee benefit plan In January 2019, the Company adopted a 401(k) retirement and savings plan (the 401(k) Plan) covering all employees. The 401(k) Plan allows employees to make pre- and post-tax contributions up to the maximum allowable amount set by the IRS. The Company has not made a matching contribution since plan inception.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	17. Subsequent events In October 2021, the Company entered into an Option and License Agreement with Beam Therapeutics Inc. (Beam), pursuant to which Beam granted to the Company a non-exclusive license to use Beam’s proprietary CRISPR Cas12b nuclease editing technology to research, develop and commercialize engineered cell therapy products that (i) are directed to certain antigen targets, with respect to the Company’s allogeneic T cell programs, or (ii) comprise certain human cell types, with respect to the Company’s stem cell-derived programs. Pursuant to the agreement, the Company made an upfront payment of $50.0 million to Beam. Additionally, the Company will be obligated to pay to Beam up to $65.0 million for each licensed product in specified developmental and commercial milestone payments and royalties on licensed products. A member of the Company’s board of directors is a beneficial owner of greater than 10% of the outstanding shares of Beam and is affiliated with a member of the board of directors of Beam

Summary of Significant Accoun_2

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 include the accounts of the Company and its wholly-owned subsidiaries. The Company’s condensed consolidated financial statements have been prepared in accordance with generally accepted accounting principles in the United States (GAAP). Certain prior period amounts have been reclassified to conform to current period presentation.
Use of estimates	Use of estimates The preparation of the financial statements in conformity with GAAP requires management to make estimates and assumptions that affect the amounts reported in the financial statements and accompanying notes. The Company evaluates its estimates and assumptions on an ongoing basis using historical experience and other factors and adjusts those estimates and assumptions when facts and circumstances dictate. Actual results could materially differ from those estimates. The most significant estimates in the Company’s condensed consolidated financial statements relate to success payment liabilities, contingent consideration, business combinations, accrued expenses, and the valuation of stock options.
Recent accounting pronouncements	Recent accounting pronouncements Recently adopted Accounting Standards Updates (ASU) No. 2016-13, Financial Instruments—Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements, ASU No. 2019-05 Financial Instruments—Credit Losses (Topic 326): Targeted Transition Relief, ASU No. 2019-11, Codification Improvements to Topic 326, Financial Instruments—Credit Losses In June 2016, the Financial Accounting Standards Board (FASB) issued ASU 2016-13, Financial Instruments—Credit Losses (Topic 362): Measurement of Credit Losses on Financial Statements (ASU 2016-13). The new standard requires that expected credit losses relating to financial assets measured on an amortized cost basis and available-for-sale debt securities be recorded through an allowance for credit losses. It also limits the amount of credit losses to be recognized for available-for-sale debt securities to the amount by which the carrying value exceeds fair value and also requires the reversal of previously recognized credit losses if fair value increases. The targeted transition relief standard allows companies an option to irrevocably elect the fair value option of ASC 825-10, Financial Instruments-Overall, applied on an instrument-by-instrument basis for eligible instruments. The Company adopted ASU 2016-13 effective January 1, 2021. The adoption of the guidance did not have a material impact on the condensed consolidated financial statements and related disclosures, and there was no allowance for losses on available-for-sale debt securities attributable to credit risk for the three and nine months ended September 30, 2021. Not yet adopted ASU No. 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment In January 2017, the FASB issued ASU 2017-04, Intangibles—Goodwill and Other (Topic 350): Simplifying the Test for Goodwill Impairment (ASU 2017-04). To address concerns over the cost and complexity of the two-step goodwill impairment test, the amendments in this ASU remove the second step of the test. An entity will instead apply a one-step quantitative test and record the amount of goodwill impairment as the excess of a reporting unit’s carrying amount over its fair value, not to exceed the total amount of goodwill allocated to the reporting unit. The new guidance does not amend the optional qualitative assessment of goodwill impairment. The new standard will be effective beginning January 1, 2023. The adoption of ASU 2017-04 is not expected to have a material impact on the Company’s consolidated financial statements.

Acquisitions - (Tables)

Acquisitions - (Tables)	9 Months Ended
	Sep. 30, 2021
Cobalt Biomedicine, Inc
Business Acquisition [Line Items]
Schedule of Various Thresholds for Market Capitalizations Resulting Potential Success Payment and Additional Potential Contingent Consideration	The following table sets forth various thresholds for the Company’s market capitalizations as of the date of a change of control and the resulting potential Cobalt Success Payment and additional potential Cobalt Contingent Consideration: Sana market capitalization upon a change of control and resulting impact to Cobalt Success Payment and additional potential Cobalt Contingent Consideration Cobalt Success Payment Additional potential Cobalt Contingent Consideration (in millions) Equal to or exceeds $8.1 billion $ 500 $ - Equal to or exceeds $7.4 billion, but less than $8.1 billion 150 350 Equal to or exceeds $6.8 billion, but less than $7.4 billion 100 400 Less than $6.8 billion - 500

License and collaboration agr_2

License and collaboration agreements (Tables)	9 Months Ended
	Sep. 30, 2021
License And Collaboration Agreements [Abstract]
Summary of Potential Success Payments	The following table summarizes the potential success payments and common stock price required for payment: Multiple of Equity Value at Issuance 5x 10x 20x 30x 40x Per share common stock price required for payment $ 20.00 $ 40.00 $ 80.00 $ 120.00 $ 160.00 Success payment(s) (in millions) $ 5.0 $ 15.0 $ 30.0 $ 50.0 $ 75.0

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Assets and Liabilities Measured on Recurring Basis	The following tables summarize the Company’s financial assets and liabilities measured at fair value on a recurring basis based on the three-tier fair value hierarchy: September 30, 2021 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value (in thousands) Financial assets: Cash equivalents: Money market funds Level 1 $ 379,336 $ - $ - $ 379,336 Corporate debt securities Level 2 121 - - 121 Total cash equivalents 379,457 - - 379,457 Short-term marketable securities: U.S. government and agency securities Level 2 76,538 18 - 76,556 Corporate debt securities Level 2 93,504 4 (23 ) 93,485 Total short-term marketable securities 170,042 22 (23 ) 170,041 Long-term marketable securities: U.S. government and agency securities Level 2 226,861 24 (81 ) 226,804 Corporate debt securities Level 2 35,621 - (24 ) 35,597 Total long-term marketable securities 262,482 24 (105 ) 262,401 Total financial assets $ 811,981 $ 46 $ (128 ) $ 811,899 Financial liabilities: Short-term financial liabilities: Contingent consideration Level 3 $ 43,459 $ - $ - $ 43,459 Success payment liabilities Level 3 5,000 - - 5,000 Total short-term financial liabilities 48,459 - - 48,459 Long-term financial liabilities: Contingent consideration Level 3 88,522 - - 88,522 Success payment liabilities Level 3 129,192 - - 129,192 Total long-term financial liabilities 217,714 - - 217,714 Total financial liabilities $ 266,173 $ - $ - $ 266,173 December 31, 2020 Valuation Hierarchy Amortized Cost Gross Unrealized Holding Gains Gross Unrealized Holding Losses Estimated Fair Value (in thousands) Financial assets: Cash equivalents: Money market funds Level 1 $ 48,359 $ - $ - $ 48,359 U.S. government and agency securities Level 2 40,727 1 (1 ) 40,727 Corporate debt securities Level 2 1,138 - - 1,138 Total cash equivalents 90,224 1 (1 ) 90,224 Short-term marketable securities: U.S. government and agency securities Level 2 244,637 30 (5 ) 244,662 Corporate debt securities Level 2 8,798 - (2 ) 8,796 Total short-term marketable securities 253,435 30 (7 ) 253,458 Long-term marketable securities: U.S. government and agency securities Level 2 33,724 7 - 33,731 Total long-term marketable securities 33,724 7 - 33,731 Total financial assets $ 377,383 $ 38 $ (8 ) $ 377,413 Financial liabilities: Long-term financial liabilities: Contingent consideration Level 3 $ 121,901 $ - $ - $ 121,901 Success payment liabilities Level 3 76,494 - - 76,494 Total financial liabilities $ 198,395 $ - $ - $ 198,395
Changes in Estimated Fair Value of Level 3 Financial Liabilities	The following table sets forth a summary of the changes in the fair value of the Company’s Level 3 financial liabilities: Contingent Consideration Cobalt Success Payment Liability Harvard Success Payment Liability (in thousands) Balance as of December 31, 2020 $ 121,901 $ 64,694 $ 11,800 Changes in fair value - expense (gain) 11,393 91,757 23,900 Balance as of March 31, 2021 133,294 156,451 35,700 Changes in fair value - expense (gain) 7,163 (66,632 ) (16,556 ) Balance as of June 30, 2021 140,457 89,819 19,144 Changes in fair value - expense (gain) (8,476 ) 21,790 3,439 Balance as of September 30, 2021 $ 131,981 $ 111,609 $ 22,583
Cobalt Contingent Consideration
Summary of Estimated Fair Value of Liabilities using Unobservable Inputs	The fair value of the Cobalt Contingent Consideration was calculated using the following unobservable inputs: September 30, 2021 December 31, 2020 Unobservable Input Range Weighted-Average Range Weighted-Average Discount rates 10.8% - 11.6% 11.1% 10.5% - 10.8% 10.6% Probability of milestone achievement 5.0% - 65.0% 27.9% 2.5% - 65.0% 27.6%
Success Payment Liabilities
Summary of Estimated Fair Value of Liabilities using Unobservable Inputs	The fair values of the Cobalt and Harvard success payment liabilities were calculated using the following unobservable inputs: September 30, 2021 December 31, 2020 Unobservable Input Cobalt Harvard Cobalt Harvard Expected stock price volatility 70% 70% 70% 70% Expected term (years) 17.4 9.5 18.1 10.2

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	9 Months Ended
	Sep. 30, 2021
Property Plant And Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net consists of the following: September 30, 2021 December 31, 2020 (in thousands) Laboratory equipment $ 41,585 $ 26,958 Leasehold improvements 26,109 15,598 Construction in progress 10,293 11,180 Computer equipment, software, and other 930 776 Total property and equipment, at cost 78,917 54,512 Less: Accumulated depreciation (15,472 ) (7,737 ) Property and equipment, net $ 63,445 $ 46,775

Accrued Liabilities (Tables)

Accrued Liabilities (Tables)	9 Months Ended
	Sep. 30, 2021
Payables And Accruals [Abstract]
Schedule of Accrued Compensation and Accrued Expenses and Other Current Liabilities	Accrued compensation and accrued expenses and other current liabilities consist of the following: September 30, 2021 December 31, 2020 (in thousands) Accrued compensation: Accrued bonuses $ 9,670 $ 11,582 Accrued payroll 5,543 1,660 Accrued paid time off 4,981 2,441 Other accrued compensation 24 337 Total accrued compensation $ 20,218 $ 16,020 Accrued expenses and other current liabilities: Accrued research and development $ 4,358 $ 1,197 Accrued property and equipment 3,178 2,892 Accrued professional fees 2,209 1,717 Other accrued current liabilities 3,139 3,660 Total accrued expenses and other current liabilities $ 12,884 $ 9,466

Commitments and Contingencies (

Commitments and Contingencies (Tables)	9 Months Ended
	Sep. 30, 2021
Commitments And Contingencies Disclosure [Abstract]
Schedule of Additional Information Related to Operating Leases	The following table contains additional information related to our operating leases: Location Approximate Square Footage Commencement Dates Expiration Dates Seattle, WA 48,086 March 2019 to September 2020 December 2026 to April 2028 Cambridge, MA 56,859 March 2019 to May 2020 November 2025 to February 2028 South San Francisco, CA 66,075 December 2019 to September 2021 April 2024 to April 2030 Fremont, CA 163,193 July 2021 November 2031
Summary of Lease Costs	The following table summarizes the Company’s lease costs: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Operating lease cost $ 4,303 $ 2,750 $ 11,368 $ 7,870 Short-term lease cost - 474 512 1,418 Variable lease cost 1,286 837 4,015 2,306 Total lease cost $ 5,589 $ 4,061 $ 15,895 $ 11,594
Reconciliation of Undiscounted Operating Lease Cash Flows by Fiscal Year to Present Value of Operating Lease Liabilities	The following table reconciles the Company’s undiscounted operating lease cash flows by fiscal year, to the present value of the operating lease liabilities as of September 30, 2021 (in thousands): 2021 (remaining 3 months) $ 2,867 2022 17,511 2023 17,677 2024 17,036 2025 17,151 2026 and thereafter 98,614 Total undiscounted lease payments 170,856 Less: imputed interest (67,513 ) Less: tenant improvement allowances (4,438 ) Present value of operating lease liabilities $ 98,905

Stock-Based Compensation (Table

Stock-Based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Schedule of Stock Based Compensation Expense Recognized	Stock-based compensation expense is recognized in the condensed consolidated statements of operations as follows: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands) Research and development $ 4,072 $ 980 $ 9,888 $ 2,555 General and administrative 1,878 186 5,161 482 Total stock-based compensation expense $ 5,950 $ 1,166 $ 15,049 $ 3,037
Schedule of Unrecognized Stock-Based Compensation Costs Related to Unvested Awards and Weighted-Average Period Over Which Costs are Expected to be Recognized	Unrecognized stock-based compensation costs related to unvested awards and the weighted-average period over which the costs are expected to be recognized as of September 30, 2021 are as follows: Stock Options RSAs RSUs Unrecognized stock-based compensation expense (in thousands) $ 79,637 $ 2,166 $ 887 Weighted-average period costs expected to be recognized (years) 2.8 1.1 1.5
Summary of Stock Option Activity	A summary of the Company’s stock option activity is as follows: Stock Options (in thousands) Weighted- Average Exercise Price per Share Weighted-Average Remaining Contractual Life (years) Aggregate Intrinsic Value (in thousands) Outstanding as of December 31, 2020 15,677 $ 4.52 Granted 3,398 23.26 Exercised (1,121 ) 1.99 Forfeited/Cancelled (671 ) 5.05 Outstanding as of September 30, 2021 17,283 $ 8.34 8.9 $ 244,590 Exercisable as of September 30, 2021 2,874 $ 2.05 8.2 $ 58,832
Schedule of Assumptions Used in Black-Scholes Option-Pricing Model for Estimating Fair Value of Stock Options Granted	The fair value of stock options granted to employees, directors, and consultants was estimated on the date of grant using the Black-Scholes option pricing model using the following assumptions: Nine Months Ended September 30, Assumptions 2021 2020 Risk free interest rate 0.46% - 1.15% 0.36% - 1.51% Expected volatility 70 % 70 % Expected term (years) 5.50 - 6.40 6.25 - 6.75 Expected dividend 0 % 0 %
Summary of Additional Information Related to Stock Option Activity	The following table summarizes additional information related to stock option activity: Nine Months Ended September 30, 2021 2020 Weighted average grant date fair value per share for options granted $ 14.64 $ 0.54 Aggregate intrinsic value of stock options exercised (in thousands) $ 22,187 $ 205
Summary of RSA Activity	A summary of the Company’s RSA activity is as follows: RSAs (in thousands) Weighted-Average Grant Date Fair Value per Share Unvested shares as of December 31, 2020 10,079 $ 0.33 Vested (4,273 ) 0.25 Forfeited (15 ) 0.73 Unvested shares as of September 30, 2021 5,791 $ 0.39

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Summary of Calculation of Basic and Diluted Net Loss Per Share of Common Stock	The following table summarizes the calculation of basic and diluted net loss per share of common stock: Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 (in thousands, except per share amounts) Net loss $ (83,263 ) $ (51,452 ) $ (245,197 ) $ (172,135 ) Weighted-average number of common shares - basic and diluted 181,827 13,680 160,515 12,249 Net loss per common share - basic and diluted $ (0.46 ) $ (3.76 ) $ (1.53 ) $ (14.05 )
Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share	The following securities were excluded from the computation of net loss per diluted share of common stock for periods presented as their effect would have been anti-dilutive: Nine Months Ended September 30, 2021 2020 (in thousands) Convertible preferred stock - 134,113 Options issued and outstanding 17,284 9,677 Unvested restricted common stock 5,791 11,952 Unvested RSUs 150 326 Total 23,225 156,068

Organization - Additional Infor

Organization - Additional Information (Details) $ / shares in Units, $ in Thousands	1 Months Ended		3 Months Ended	9 Months Ended
	Feb. 28, 2021USD ($)$ / sharesshares	Jan. 31, 2021	Mar. 31, 2021shares	Sep. 30, 2021USD ($)shares	Dec. 31, 2020USD ($)shares	Sep. 30, 2020shares	Jun. 30, 2020shares	Mar. 31, 2020shares	Dec. 31, 2019shares
Description Of Organization [Line Items]
Entity incorporation, date of Incorporation				Jul. 13, 2018
Reverse stock split, conversion ratio		0.25
Reverse stock split, description				In January 2021, the Company’s board of directors approved an amendment to the Company’s amended and restated certificate of incorporation to effect a 1-for-4 reverse stock split of shares of the Company’s common and convertible preferred stock, which was effected on January 27, 2021.
Proceeds from public offering of common stock, net of offering costs				$ 626,405
Convertible preferred stock, shares outstanding | shares				0	134,113,000
Accumulated deficit				$ 674,629	$ 429,432
Cash, cash equivalents and marketable securities				866,100
Success payment liabilities				131,800
Contingent consideration				$ 80,700
Convertible Preferred Stock
Description Of Organization [Line Items]
Convertible preferred stock, shares outstanding | shares				0	134,113,000	134,113,000	134,113,000	106,890,000	106,890,000
Common Stock
Description Of Organization [Line Items]
Conversion of preferred stock into common stock (in shares) | shares			134,113,000
IPO
Description Of Organization [Line Items]
Convertible preferred stock, shares outstanding | shares	134,100,000
IPO | Convertible Preferred Stock
Description Of Organization [Line Items]
Conversion of preferred stock into common stock (in shares) | shares	134,100,000
Carrying value of converted preferred stock	$ 852,900
IPO | Common Stock
Description Of Organization [Line Items]
Issuance of common stock in initial public offering, net of offering costs (in shares) | shares	27,000,000		27,025,000
Common stock price per share | $ / shares	$ 25
Proceeds from public offering of common stock, net of offering costs	$ 626,400
Payments of underwriting discounts and commissions	45,200
Offering expenses	$ 4,000
Underwriters' Option To Purchase Additional Shares | Common Stock
Description Of Organization [Line Items]
Issuance of common stock in initial public offering, net of offering costs (in shares) | shares	3,500,000

Summary of Significant Accoun_3

Summary of Significant Accounting Policies - Additional Information (Details)	Sep. 30, 2021USD ($)
Summary Of Significant Accounting Policies [Line Items]
Allowance for losses on available-for-sale debt securities	$ 0
ASU 2016-13
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

Acquisitions - Additional Infor

Acquisitions - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Sep. 30, 2020	Feb. 28, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Business Acquisition [Line Items]
Estimated fair value of contingent consideration, short term liabilities			$ 43,459,000		$ 43,459,000
Estimated fair value of contingent consideration, long-term liabilities			88,522,000		88,522,000		$ 121,901,000
Change in the estimated fair value of contingent consideration					10,080,000	$ 16,672,000
Oscine Corp
Business Acquisition [Line Items]
Business acquisition, consideration transferred	$ 8,500,000
Oscine Corp | Stock Purchase Agreement
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired	100.00%			100.00%		100.00%
Business acquisition, consideration transferred	$ 8,500,000			$ 8,500,000
Business acquisition, consideration transferred, cash	7,600,000
Business acquisition, consideration holdback amount	900,000
Oscine Corp | Stock Purchase Agreement | Maximum
Business Acquisition [Line Items]
Future milestone payments upon achievement of certain development and commercial milestones	$ 225,800,000			225,800,000		$ 225,800,000
Cobalt Biomedicine, Inc | Acquisition Agreement
Business Acquisition [Line Items]
Business acquisition, percentage of voting interests acquired		100.00%
Maximum success payment upon achievement of certain pre-specified development milestones		$ 500,000,000
Maximum period for success payment to achieve		20 years
Cobalt Biomedicine, Inc | Acquisition Agreement | Research and Development
Business Acquisition [Line Items]
Estimated fair value of success payment liability			111,600,000		111,600,000		64,700,000
Estimated fair value of contingent consideration			132,000,000		132,000,000		$ 121,900,000
Estimated fair value of contingent consideration, short term liabilities			43,500,000		43,500,000
Estimated fair value of contingent consideration, long-term liabilities			88,500,000		88,500,000
(Gain) expense in connection with change in estimated fair value of success payment			21,800,000	1,300,000	46,900,000	35,200,000
Change in the estimated fair value of contingent consideration			$ 8,500,000	$ 2,300,000	$ 10,100,000	$ 16,700,000
Cobalt Biomedicine, Inc | Acquisition Agreement | Market Capitalization Equal to or Exceeds $8.1 billion
Business Acquisition [Line Items]
Cobalt success payment		$ 500,000,000
Cobalt Biomedicine, Inc | Acquisition Agreement | Minimum [Member]
Business Acquisition [Line Items]
Threshold market capitalization		$ 8,100,000,000

Acquisitions - Schedule of Vari

Acquisitions - Schedule of Various Thresholds for Market Capitalizations Resulting Potential Success Payment and Additional Potential Contingent Consideration (Details) - Cobalt Biomedicine, Inc $ in Millions	1 Months Ended
	Feb. 28, 2019USD ($)
Market Capitalization Equal to or Exceeds $8.1 billion
Business Acquisition [Line Items]
Cobalt Success Payment	$ 500
Market Capitalization Equal to or exceeds $7.4 billion, but less than $8.1 billion
Business Acquisition [Line Items]
Cobalt Success Payment	150
Additional potential Cobalt Contingent Consideration	350
Market Capitalization Equal to or exceeds $6.8 billion, but less than $7.4 billion
Business Acquisition [Line Items]
Cobalt Success Payment	100
Additional potential Cobalt Contingent Consideration	400
Market Capitalization Less than $6.8 billion
Business Acquisition [Line Items]
Additional potential Cobalt Contingent Consideration	$ 500

Acquisitions - Schedule of Va_2

Acquisitions - Schedule of Various Thresholds for Market Capitalizations Resulting Potential Success Payment and Additional Potential Contingent Consideration (Parenthetical) (Details) - Sana $ in Billions	Feb. 28, 2019USD ($)
Market Capitalization Equal to or Exceeds $8.1 billion
Business Acquisition [Line Items]
Threshold market capitalization	$ 8.1
Market Capitalization Equal to or exceeds $7.4 billion, but less than $8.1 billion
Business Acquisition [Line Items]
Threshold market capitalization	7.4
Market Capitalization Equal to or exceeds $6.8 billion, but less than $7.4 billion
Business Acquisition [Line Items]
Threshold market capitalization	6.8
Market Capitalization Less than $6.8 billion
Business Acquisition [Line Items]
Threshold market capitalization	$ 6.8

Intangible Asset and Goodwill -

Intangible Asset and Goodwill - Additional Information (Details) - USD ($)	9 Months Ended	11 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2019	Dec. 31, 2020
Goodwill And Intangible Assets Disclosure [Abstract]
Intangible asset	$ 59,195,000		$ 59,195,000
Amortization of intangible asset	0
Goodwill	140,627,000		140,627,000
Impairments of intangible asset or goodwill	$ 0	$ 0	$ 0

License and Collaboration Agr_3

License and Collaboration Agreements - Additional Information (Details) - USD ($)	1 Months Ended		3 Months Ended		9 Months Ended
	Jun. 30, 2020	Mar. 31, 2019	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Series B Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Share issue price							$ 16
Harvard College
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Share issue price		$ 4
Maximum period expected to achieve for success payments		12 years
Estimated fair value of success payment liability			$ 22,600,000		$ 22,600,000		$ 11,800,000
Harvard College | Series B Convertible Preferred Stock
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
License payment upon closing of equity financing	$ 6,000,000
Harvard College | Research and Development
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Expense in connection with change in estimated fair value of success payment liability			3,400,000	$ 800,000	10,800,000	$ 5,500,000
Harvard College | Short-term Liabilities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fair value of success payment liability			5,000,000		5,000,000		0
Harvard College | Long-term Liabilities
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Estimated fair value of success payment liability			$ 17,600,000		$ 17,600,000		$ 11,800,000
Harvard College | Maximum
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Potential success payment		$ 175,000,000

License and Collaboration Agr_4

License and Collaboration Agreements - Summary of Potential Success Payments (Details) - Harvard College $ / shares in Units, $ in Millions	1 Months Ended
	Mar. 31, 2019USD ($)$ / shares
Multiple of Equity Value at Issuance, 5x
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Per share common stock price required for payment | $ / shares	$ 20
Success payment(s) | $	$ 5
Multiple of Equity Value at Issuance, 10x
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Per share common stock price required for payment | $ / shares	$ 40
Success payment(s) | $	$ 15
Multiple of Equity Value at Issuance, 20x
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Per share common stock price required for payment | $ / shares	$ 80
Success payment(s) | $	$ 30
Multiple of Equity Value at Issuance, 30x
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Per share common stock price required for payment | $ / shares	$ 120
Success payment(s) | $	$ 50
Multiple of Equity Value at Issuance, 40x
Collaborative Arrangements And Noncollaborative Arrangement Transactions [Line Items]
Per share common stock price required for payment | $ / shares	$ 160
Success payment(s) | $	$ 75

Restricted Cash - Additional In

Restricted Cash - Additional Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Restricted Cash And Cash Equivalents [Abstract]
Standby letters of credit	$ 8,819	$ 2,143
Restricted cash and cash equivalents, noncurrent, nature of restriction, description	standby letters of credit

Fair Value Measurements - Summa

Fair Value Measurements - Summary of Financial Assets and Liabilities Measured at Fair Value on Recurring Basis (Details) - Fair Value, Recurring - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Cash Equivalents
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	$ 379,457	$ 90,224
Gross Unrealized Holding Gains	0	1
Gross Unrealized Holding Losses	0	(1)
Estimated Fair Value	379,457	90,224
Cash Equivalents | Money Market Funds | Level 1
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	379,336	48,359
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	379,336	48,359
Cash Equivalents | Corporate Debt Securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	121	1,138
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	121	1,138
Cash Equivalents | US Government and Agencies Securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost		40,727
Gross Unrealized Holding Gains		1
Gross Unrealized Holding Losses		(1)
Estimated Fair Value		40,727
Short-term Marketable Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	170,042	253,435
Gross Unrealized Holding Gains	22	30
Gross Unrealized Holding Losses	(23)	(7)
Estimated Fair Value	170,041	253,458
Short-term Marketable Securities | Corporate Debt Securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	93,504	8,798
Gross Unrealized Holding Gains	4	0
Gross Unrealized Holding Losses	(23)	(2)
Estimated Fair Value	93,485	8,796
Short-term Marketable Securities | US Government and Agencies Securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	76,538	244,637
Gross Unrealized Holding Gains	18	30
Gross Unrealized Holding Losses	0	(5)
Estimated Fair Value	76,556	244,662
Long-term Marketable Securities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	262,482	33,724
Gross Unrealized Holding Gains	24	7
Gross Unrealized Holding Losses	(105)	0
Estimated Fair Value	262,401	33,731
Long-term Marketable Securities | Corporate Debt Securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	35,621
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	(24)
Estimated Fair Value	35,597
Long-term Marketable Securities | US Government and Agencies Securities | Level 2
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	226,861	33,724
Gross Unrealized Holding Gains	24	7
Gross Unrealized Holding Losses	(81)	0
Estimated Fair Value	226,804	33,731
Financial Assets
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	811,981	377,383
Gross Unrealized Holding Gains	46	38
Gross Unrealized Holding Losses	(128)	(8)
Estimated Fair Value	811,899	377,413
Short-term Financial Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	48,459
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	0
Estimated Fair Value	48,459
Short-term Financial Liabilities | Contingent Consideration | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	43,459
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	0
Estimated Fair Value	43,459
Short-term Financial Liabilities | Success Payment Liabilities | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	5,000
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	0
Estimated Fair Value	5,000
Long-term Financial Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	217,714
Gross Unrealized Holding Gains	0
Gross Unrealized Holding Losses	0
Estimated Fair Value	217,714
Long-term Financial Liabilities | Contingent Consideration | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	88,522	121,901
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	88,522	121,901
Long-term Financial Liabilities | Success Payment Liabilities | Level 3
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	129,192	76,494
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	129,192	76,494
Financial Liabilities
Fair Value Balance Sheet Grouping Financial Statement Captions [Line Items]
Amortized Cost	266,173	198,395
Gross Unrealized Holding Gains	0	0
Gross Unrealized Holding Losses	0	0
Estimated Fair Value	$ 266,173	$ 198,395

Fair Value Measurements - Addit

Fair Value Measurements - Additional Information (Details) - USD ($)	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Realized gains or losses recognized on sale or maturity of available-for-sale securities	$ 0	$ 0	$ 0	$ 0
Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Marketable securities maturity period			2 years
Investments in securities with maturities period			1 year

Fair Value Measurements - Chang

Fair Value Measurements - Changes in Estimated Fair Value of Level 3 Financial Liabilities (Details) - Level 3 - USD ($) $ in Thousands	3 Months Ended
	Sep. 30, 2021	Jun. 30, 2021	Mar. 31, 2021
Contingent Consideration
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	$ 140,457	$ 133,294	$ 121,901
Changes in fair value - expense (gain)	(8,476)	7,163	11,393
Ending Balance	131,981	140,457	133,294
Cobalt Success Payment Liability
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	89,819	156,451	64,694
Changes in fair value - expense (gain)	21,790	(66,632)	91,757
Ending Balance	111,609	89,819	156,451
Harvard Success Payment Liabilitiy
Fair Value Liabilities Measured On Recurring Basis Unobservable Input Reconciliation [Line Items]
Beginning Balance	19,144	35,700	11,800
Changes in fair value - expense (gain)	3,439	(16,556)	23,900
Ending Balance	$ 22,583	$ 19,144	$ 35,700

Fair Value Measurements - Sum_2

Fair Value Measurements - Summary of Estimated Fair Value of Contingent Consideration Unobservable Inputs (Details) - Cobalt Contingent Consideration	Sep. 30, 2021	Dec. 31, 2020
Discount Rates | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.108	0.105
Discount Rates | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.116	0.108
Discount Rates | Weighted-Average
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.111	0.106
Probability of Milestone Achievement | Minimum [Member]
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.050	0.025
Probability of Milestone Achievement | Maximum
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.650	0.650
Probability of Milestone Achievement | Weighted-Average
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.279	0.276

Fair Value Measurements - Sum_3

Fair Value Measurements - Summary of Estimated Fair Value of Success Payment Liabilities Unobservable Inputs (Details)	9 Months Ended	12 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Expected Stock Price Volatility | Cobalt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.70	0.70
Expected Stock Price Volatility | Harvard
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input	0.70	0.70
Expected Term (Years) | Cobalt
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input expected term (years)	17 years 4 months 24 days	18 years 1 month 6 days
Expected Term (Years) | Harvard
Fair Value Assets And Liabilities Measured On Recurring And Nonrecurring Basis [Line Items]
Fair value contingent consideration measurement input expected term (years)	9 years 6 months	10 years 2 months 12 days

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 78,917	$ 54,512
Less: Accumulated depreciation	(15,472)	(7,737)
Property and equipment, net	63,445	46,775
Laboratory Equipment
Property Plant And Equipment [Line Items]
Property and equipment, at cost	41,585	26,958
Leasehold Improvements
Property Plant And Equipment [Line Items]
Property and equipment, at cost	26,109	15,598
Construction In Progress
Property Plant And Equipment [Line Items]
Property and equipment, at cost	10,293	11,180
Computer Equipment, Software and Other
Property Plant And Equipment [Line Items]
Property and equipment, at cost	$ 930	$ 776

Property and Equipment, Net - A

Property and Equipment, Net - Additional Information (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Property Plant And Equipment [Abstract]
Depreciation expense	$ 2,800	$ 1,600	$ 7,735	$ 4,166

Accrued Liabilities - Schedule

Accrued Liabilities - Schedule of Accrued Compensation and Accrued Expenses and Other Current Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Accrued compensation:
Accrued bonuses	$ 9,670	$ 11,582
Accrued payroll	5,543	1,660
Accrued paid time off	4,981	2,441
Other accrued compensation	24	337
Total accrued compensation	20,218	16,020
Accrued expenses and other current liabilities:
Accrued research and development	4,358	1,197
Accrued property and equipment	3,178	2,892
Accrued professional fees	2,209	1,717
Other accrued current liabilities	3,139	3,660
Total accrued expenses and other current liabilities	$ 12,884	$ 9,466

Commitments and Contingencies -

Commitments and Contingencies - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021Extension
Lessee Lease Description [Line Items]
Lease arrangement, contractual expiration period, beginning year	2024-04
Lease arrangement, contractual expiration period, ending year	2031-11
Weighted-average remaining lease term	7 years 10 months 24 days
Weighted-average incremental borrowing rate	9.55%
Seattle Operating Lease Agreement
Lessee Lease Description [Line Items]
Operating lease, renew period	5 years
Lessee, operating lease, existence of option to extend [true false]	true
Lessee, operating lease, option to extend	The Seattle and South San Francisco lease agreements each provide the Company with the option to renew for an additional period of five years
South San Francisco Operating Lease Agreement
Lessee Lease Description [Line Items]
Operating lease, renew period	5 years
Lessee, operating lease, existence of option to extend [true false]	true
Lessee, operating lease, option to extend	The Seattle and South San Francisco lease agreements each provide the Company with the option to renew for an additional period of five years
Fremont, CA.
Lessee Lease Description [Line Items]
Operating lease, renew period	5 years
Lessee, operating lease, existence of option to extend [true false]	true
Lessee, operating lease, option to extend	option to extend for up to two additional five-year terms
Lessee, operating lease, initial term	10 years
Fremont, CA. | Maximum
Lessee Lease Description [Line Items]
Number of additional extensions permitted	2

Commitments and Contingencies_2

Commitments and Contingencies - Schedule of Additional Information Related to Operating Leases (Details)	9 Months Ended
	Sep. 30, 2021ft²
Lessee Lease Description [Line Items]
Expiration Dates, Beginning	2024-04
Expiration Dates, Ending	2031-11
Seattle, WA
Lessee Lease Description [Line Items]
Approximate Square Footage	48,086
Commencement Dates, Beginning	2019-03
Commencement Dates, Ending	2020-09
Expiration Dates, Beginning	2026-12
Expiration Dates, Ending	2028-04
Cambridge, MA
Lessee Lease Description [Line Items]
Approximate Square Footage	56,859
Commencement Dates, Beginning	2019-03
Commencement Dates, Ending	2020-05
Expiration Dates, Beginning	2025-11
Expiration Dates, Ending	2028-02
South San Francisco, CA
Lessee Lease Description [Line Items]
Approximate Square Footage	66,075
Commencement Dates, Beginning	2019-12
Commencement Dates, Ending	2021-09
Expiration Dates, Beginning	2024-04
Expiration Dates, Ending	2030-04
Fremont, CA.
Lessee Lease Description [Line Items]
Approximate Square Footage	163,193
Commencement Dates, Beginning	2021-07
Expiration Dates, Ending	2031-11

Commitments and Contingencies_3

Commitments and Contingencies - Summary of Lease Costs (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Lease, Cost [Abstract]
Operating lease cost	$ 4,303	$ 2,750	$ 11,368	$ 7,870
Short-term lease cost		474	512	1,418
Variable lease cost	1,286	837	4,015	2,306
Total lease cost	$ 5,589	$ 4,061	$ 15,895	$ 11,594

Commitments and Contingencies_4

Commitments and Contingencies - Reconciliation of Undiscounted Operating Lease Cash Flows by Fiscal Year to Present Value of Operating Lease Liabilities (Details) $ in Thousands	Sep. 30, 2021USD ($)
Commitments And Contingencies Disclosure [Abstract]
2021 (remaining 3 months)	$ 2,867
2022	17,511
2023	17,677
2024	17,036
2025	17,151
2026 and thereafter	98,614
Total undiscounted lease payments	170,856
Less: imputed interest	(67,513)
Less: tenant improvement allowances	(4,438)
Present value of operating lease liabilities	$ 98,905

Convertible Preferred Stock - A

Convertible Preferred Stock - Additional Information (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended	12 Months Ended
	Sep. 30, 2020	Dec. 31, 2020	Dec. 31, 2019	Dec. 31, 2018	Sep. 30, 2021	Feb. 28, 2021	Jun. 30, 2020	Mar. 31, 2020
Class Of Stock [Line Items]
Convertible preferred stock shares issued		134,113,000			0
Gross proceeds from issuance of convertible preferred stock	$ 435,538
Outstanding shares of convertible preferred stock converted into shares of common stock						134,100,000
Convertible preferred stock outstanding		134,113,000			0
Series A-1 Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock shares issued				11,500,000
Share price				$ 4
Gross proceeds from issuance of convertible preferred stock				$ 45,900
Series A-2 Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock shares issued			56,000,000
Share price			$ 4
Gross proceeds from issuance of convertible preferred stock			$ 224,000
Series B Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock shares issued		27,200,000
Share price		$ 16
Gross proceeds from issuance of convertible preferred stock		$ 435,600
Convertible Preferred Stock
Class Of Stock [Line Items]
Convertible preferred stock outstanding	134,113,000	134,113,000	106,890,000		0		134,113,000	106,890,000

Stockholders' Equity - Addition

Stockholders' Equity - Additional Information (Details) - shares	Sep. 30, 2021	Feb. 28, 2021	Dec. 31, 2020
Class Of Stock [Line Items]
Shares authorized		800,000,000
Common stock, shares authorized	750,000,000	750,000,000	707,000,000
Preferred stock, shares authorized	50,000,000	50,000,000	0
Common stock, shares outstanding	182,908,000		16,170,000
Restricted Stock
Class Of Stock [Line Items]
Common stock outstanding	5,791,000		10,079,000

Stock-Based Compensation - Addi

Stock-Based Compensation - Additional Information (Details) - USD ($) $ in Millions	1 Months Ended	3 Months Ended		9 Months Ended
	Feb. 28, 2021	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of vested		$ 0.4	$ 0.2	$ 1.1	$ 0.6
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Fair value of vested				0.2
Unvested, RSUs		$ 0.2		0.2		$ 0.3
Granted, RSUs				$ 0.1
2021 Incentive Award Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Increase in number of shares of common stock reserved for issuance expressed as percentage of outstanding shares	5.00%
2021 Employee Stock Purchase Plan
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage related to employees able to purchase shares at lower of fair market value	85.00%
Percentage of annual increase in shares available for issuance	1.00%
2021 Employee Stock Purchase Plan | Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Percentage allowed for eligible employees to purchase shares of common stock	15.00%

Stock-Based Compensation - Sche

Stock-Based Compensation - Schedule of Stock Based Compensation Expense Recognized (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 5,950	$ 1,166	$ 15,049	$ 3,037
Research and development
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	4,072	980	9,888	2,555
General and administrative
Employee Service Share Based Compensation Allocation Of Recognized Period Costs [Line Items]
Total stock-based compensation expense	$ 1,878	$ 186	$ 5,161	$ 482

Stock-Based Compensation - Sc_2

Stock-Based Compensation - Schedule of Unrecognized Stock-Based Compensation Costs Related to Unvested Awards and Weighted-Average Period Over Which Costs are Expected to be Recognized (Details)	9 Months Ended
	Sep. 30, 2021USD ($)
Stock Options
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense (in thousands)	$ 79,637
Weighted-average period costs expected to be recognized (years)	2 years 9 months 18 days
Restricted Stock
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense (in thousands)	$ 2,166
Weighted-average period costs expected to be recognized (years)	1 year 1 month 6 days
Restricted Stock Units
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Unrecognized stock-based compensation expense (in thousands)	$ 887
Weighted-average period costs expected to be recognized (years)	1 year 6 months

Stock-Based Compensation - Summ

Stock-Based Compensation - Summary of Stock Option Activity (Details) - USD ($) $ / shares in Units, shares in Thousands, $ in Thousands	9 Months Ended
	Sep. 30, 2021
Stock Options
Stock Options Outstanding, Beginning Balance	15,677
Stock Options, Granted	3,398
Stock Options, Exercised	(1,121)
Stock Options, Forfeited/Cancelled	(671)
Stock Options Outstanding, Ending Balance	17,283
Stock Options Exercisable	2,874
Weighted-Average Exercise Price per Share
Weighted-Average Exercise Price per Share Outstanding, Beginning Balance	$ 4.52
Weighted-Average Exercise Price per Share, Granted	23.26
Weighted-Average Exercise Price per Share, Exercised	1.99
Weighted-Average Exercise Price per Share, Forfeited/Cancelled	5.05
Weighted-Average Exercise Price per Share Outstanding, Ending Balance	8.34
Weighted-Average Exercise Price Per Share Exercisable	$ 2.05
Weighted-Average Remaining Contractual Life (years)
Weighted-Average Remaining Contractual Life (years), Outstanding	8 years 10 months 24 days
Weighted-Average Remaining Contractual Life (years), Exercisable	8 years 2 months 12 days
Aggregate Intrinsic Value
Aggregate Intrinsic Value, Outstanding	$ 244,590
Aggregate Intrinsic Value, Exercisable	$ 58,832

Stock-Based Compensation - Sc_3

Stock-Based Compensation - Schedule of Assumptions Used in Black-Scholes Option-Pricing Model for Estimating Fair Value of Stock Options Granted (Details)	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Risk free interest rate, minimum	0.46%	0.36%
Risk free interest rate, maximum	1.15%	1.51%
Expected volatility	70.00%	70.00%
Expected dividend	0.00%	0.00%
Minimum [Member]
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	5 years 6 months	6 years 3 months
Maximum
Share Based Compensation Arrangement By Share Based Payment Award [Line Items]
Expected term (years)	6 years 4 months 24 days	6 years 9 months

Stock-Based Compensation - Su_2

Stock-Based Compensation - Summary of Additional Information Related to Stock Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Disclosure Of Compensation Related Costs Sharebased Payments [Abstract]
Weighted average grant date fair value per share for options granted	$ 14.64	$ 0.54
Aggregate intrinsic value of stock options exercised (in thousands)	$ 22,187	$ 205

Stock-Based Compensation - Su_3

Stock-Based Compensation - Summary of RSA Activity (Details) - Restricted Stock shares in Thousands	9 Months Ended
	Sep. 30, 2021$ / sharesshares
RSAs
Unvested shares as of December 31, 2020 | shares	10,079
Vested | shares	(4,273)
Forfeited | shares	(15)
Unvested shares as of September 30, 2021 | shares	5,791
Weighted-Average Grant Date Fair Value per Share
Unvested shares as of December 31, 2020 | $ / shares	$ 0.33
Vested | $ / shares	0.25
Forfeited | $ / shares	0.73
Unvested shares as of September 30, 2021 | $ / shares	$ 0.39

Net Income Loss Per Share - Sum

Net Income Loss Per Share - Summary of Calculation of Basic and Diluted Net Loss Per Share of Common Stock (Details) - USD ($) $ / shares in Units, shares in Thousands, $ 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	$ (83,263)	$ 18,683	$ (180,617)	$ (51,452)	$ (87,808)	$ (32,875)	$ (245,197)	$ (172,135)
Weighted-average number of common shares - basic and diluted	181,827			13,680			160,515	12,249
Net loss per common share - basic and diluted	$ (0.46)			$ (3.76)			$ (1.53)	$ (14.05)

Net Loss Per Share - Anti-dilut

Net Loss Per Share - Anti-dilutive Securities Excluded from Calculation of Diluted Net Loss Per Share (Details) - shares shares in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of dilutive net loss per share	23,225	156,068
Convertible Preferred Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of dilutive net loss per share		134,113
Options Issued and Outstanding
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of dilutive net loss per share	17,284	9,677
Restricted Stock
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of dilutive net loss per share	5,791	11,952
RSUs
Antidilutive Securities Excluded From Computation Of Earnings Per Share [Line Items]
Anti-dilutive securities excluded from computation of dilutive net loss per share	150	326

Employee Benefit Plan - Additio

Employee Benefit Plan - Additional Information (Details)	9 Months Ended
	Sep. 30, 2021USD ($)
Compensation And Retirement Disclosure [Abstract]
Matching contribution by employer under retirement and savings plan	$ 0

Subsequent Events - Additional

Subsequent Events - Additional Information (Details) - Subsequent Event - Option and License Agreement - Beam Therapeutics Inc $ in Millions	1 Months Ended
	Oct. 31, 2021USD ($)
Subsequent Event [Line Items]
Upfront payment	$ 50
Obligated to pay to Beam	$ 65
Beneficial ownership percentage	10.00%