Condensed Statements of Cash Flows (Unaudited) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2023	Sep. 30, 2022
Cash flows from operating activities:
Net loss	$ (101,733)	$ (76,453)
Adjustments to reconcile net loss to net cash used in operating activities:
Net amortization of premiums and discounts on investments in marketable securities	(3,422)	(479)
Depreciation and amortization	2,265	1,670
Non-cash lease expense	3,860	4,454
Stock-based compensation expense	8,269	9,912
Loss on disposal of assets	71	0
Impairment of assets	43,276	0
Changes in assets and liabilities:
Assets held for sale	(20)	0
Prepaid expenses and other current assets and other assets	4,884	(2,437)
Accounts payable	1,145	1,275
Accrued compensation	(1,900)	657
Accrued research costs	(690)	(280)
Accrued expenses and other current liabilities and other liabilities	2,479	399
Operating lease liabilities	(2,614)	(4,269)
Net cash used in operating activities	(44,130)	(65,551)
Cash flows from investing activities:
Purchases of property and equipment	(10,806)	(5,573)
Proceeds from sales of property and equipment	1,225	0
Purchases of investments in marketable securities	(28,130)	(339,814)
Proceeds from maturities of marketable securities	216,975	90,000
Net cash provided by (used in) investing activities	179,264	(255,387)
Cash flows from financing activities:
Proceeds from issuance of common stock upon exercise of vested stock options	34	18
Proceeds from employee stock purchase plan	157	414
Repurchase of unvested early exercised shares and founders' shares	(67)	(79)
Net cash provided by financing activities	124	353
Net increase (decrease) in cash, cash equivalents and restricted cash	135,258	(320,585)
Cash, cash equivalents and restricted cash, at beginning of period	49,446	378,692
Cash, cash equivalents and restricted cash, at end of period	184,704	58,107
Reconciliation of cash, cash equivalents and restricted cash to statement of financial position:
Cash and cash equivalents	182,988	56,391
Restricted cash	1,716	1,716
Cash, cash equivalents and restricted cash in statement of financial position	184,704	58,107
Supplemental disclosures of non-cash investing and financing information:
Property and equipment purchases in accounts payable and accrued expenses	0	(319)
Lessor funded lease incentive additions included in property and equipment	7,193	2,616
Proceeds from sale of property and equipment in accounts receivable	449	0
Additions to ROU assets from new operating lease liabilities	31,974	0
Vesting of early exercised stock options	$ 48	$ 108