Condensed Consolidated Statements of Cash Flows - USD ($) $ in Millions	6 Months Ended
	Jun. 30, 2024	Jun. 30, 2023
Cash flow from operating activities
Net loss	$ (97)	$ (155)
Adjustments to reconcile net loss to net cash used in operating activities:
Stock-based compensation expense	40	37
Depreciation and amortization	5	4
Noncash lease expense	4	4
Impairment of long-lived assets	20	0
Amortization of discounts on marketable securities	(13)	(8)
Other items, net	1	1
Changes in operating assets and liabilities:
Receivable from collaboration partners ($6 and $7 from a related party)	20	4
Other assets ($6 and ($3) from a related party)	15	(1)
Accounts payable	(1)	(9)
Deferred revenue (($90) and ($19) to a related party)	(81)	(19)
Other liabilities	(9)	(13)
Net cash used in operating activities	(96)	(155)
Cash flow from investing activities
Purchases of marketable securities	(593)	(393)
Proceeds from maturities of marketable securities	484	542
Proceeds from sales of marketable securities	7	14
Purchases of property and equipment	(4)	(8)
Net cash provided by (used in) investing activities	(106)	155
Cash flow from financing activities
Proceeds from issuance of common stock ($228 and $20 from a related party)	228	20
Proceeds from issuance of common stock pursuant to equity award plans	4	4
Payments of employee taxes related to net settlement of equity awards	(1)	0
Net cash provided by financing activities	231	24
Net increase in cash, cash equivalents and restricted cash	29	24
Cash, cash equivalents and restricted cash at beginning of period	130	209
Cash, cash equivalents and restricted cash at end of period	159	233
Non-cash investing and financing activities:
Unpaid portion of property and equipment purchases included in Accounts payable and Other current liabilities	$ 0	$ 8