Proterra (PTRAQ) 10-Q 12 Nov 21 2021 Q3 Quarterly report Financial data

Cover

Cover - shares	9 Months Ended
	Sep. 30, 2021	Nov. 08, 2021
Cover [Abstract]
Document Type	10-Q
Document Quarterly Report	true
Document Period End Date	Sep. 30, 2021
Document Transition Report	false
Entity File Number	001-39546
Entity Registrant Name	Proterra Inc
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	98-1551379
Entity Address, Address Line One	1815 Rollins Road
Entity Address, City or Town	Burlingame
Entity Address, State or Province	CA
Entity Address, Postal Zip Code	94010
City Area Code	864
Local Phone Number	438-0000
Title of 12(b) Security	Common Stock, $0.0001 par value per share
Trading Symbol	PTRA
Security Exchange Name	NASDAQ
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	true
Entity Ex Transition Period	true
Entity Shell Company	false
Entity Common Stock, Shares Outstanding		218,306,979
Entity Central Index Key	0001820630
Amendment Flag	false
Current Fiscal Year End Date	--12-31
Document Fiscal Year Focus	2021
Document Fiscal Period Focus	Q3

CONDENSED CONSOLIDATED BALANCE

CONDENSED CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Assets:
Cash and cash equivalents	$ 280,537	$ 110,719
Accounts receivable, net	59,939	51,716
Short-term investments	446,951	68,990
Inventory	102,695	92,330
Prepaid expenses and other current assets	12,526	7,455
Deferred cost of goods sold	1,862	2,037
Restricted cash, current	10,890	8,397
Total current assets	915,400	341,644
Property, plant, and equipment, net	53,059	53,587
Operating lease right-of-use assets	9,234	10,310
Restricted cash, non-current	1,675	4,581
Other assets	6,701	4,789
Total assets	986,069	414,911
Liabilities and Stockholders’ Equity:
Accounts payable	43,693	25,074
Accrued liabilities	23,060	19,736
Deferred revenue, current	9,379	16,015
Operating lease liabilities, current	3,583	3,153
Debt, current	10,000	0
Total current liabilities	89,715	63,978
Debt, non-current	95,896	133,252
Derivative liability	0	70,870
Warrant liability	56,133	39,670
Deferred revenue, non-current	18,169	12,206
Operating lease liabilities, non-current	6,303	7,891
Other long-term liabilities	13,490	12,578
Total liabilities	279,706	340,445
Commitments and contingencies (Note 8)
Stockholders’ equity:
Common stock, $0.0001 par value; 500,000 shares authorized and 212,827 shares issued and outstanding as of September 30, 2021 (unaudited); 156,277 shares authorized and 5,678 shares issued and outstanding as of December 31, 2020	21	1
Additional paid-in capital	1,519,429	682,671
Accumulated deficit	(813,087)	(608,219)
Total stockholders’ equity	706,363	74,466
Total liabilities and stockholders’ equity	986,069	414,911
Convertible preferred stock, $0.0001 par value; zero shares authorized, zero shares issued and outstanding as of September 30, 2021 (unaudited), 115,644 shares authorized and 115,136 shares issued and outstanding as of December 31, 2020; liquidation preference zero as of September 30, 2021 (unaudited) and $631.3 million as of December 31, 2020
Stockholders’ equity:
Preferred stock	0	13
Preferred stock, $0.0001 par value; 10,000 shares authorized and zero shares issued and outstanding as of September 30, 2021 (unaudited); zero shares authorized, issued and outstanding as of December 31, 2020
Stockholders’ equity:
Preferred stock	$ 0	$ 0

CONDENSED CONSOLIDATED BALANC_2

CONDENSED CONSOLIDATED BALANCE SHEETS (Parenthetical) - USD ($) $ in Millions	Sep. 30, 2021	Dec. 31, 2020
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	10,000,000	0
Preferred stock, shares issued (in shares)	0	0
Preferred stock, shares outstanding (in shares)	0	0
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	500,000,000	156,277,000
Common stock, shares issued (in shares)	212,827,249	5,678,000
Common stock, shares outstanding (in shares)	212,827,249	5,678,000
Convertible preferred stock
Preferred stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Preferred stock, shares authorized (in shares)	0	115,644,000
Preferred stock, shares issued (in shares)	0	115,136,000
Preferred stock, shares outstanding (in shares)	0	115,136,000
Preferred stock, liquidation preference	$ 0	$ 631.3

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
Total revenue	$ 61,941	$ 47,537	$ 174,449	$ 142,796
Total cost of goods sold	59,278	45,628	169,602	136,367
Gross profit	2,663	1,909	4,847	6,429
Research and development	11,296	9,229	31,311	26,133
Selling, general and administrative	21,123	15,240	60,327	47,165
Total operating expenses	32,419	24,469	91,638	73,298
Loss from operations	(29,756)	(22,560)	(86,791)	(66,869)
Interest expense, net	6,362	5,198	44,288	6,564
(Gain) loss on valuation of derivative and warrant liabilities	(73,197)	19,061	72,913	19,061
Other expense, net	758	41	876	1,890
Income (loss) before income taxes	36,321	(46,860)	(204,868)	(94,384)
Provision for income taxes	0	0	0	0
Net income (loss)	$ 36,321	$ (46,860)	$ (204,868)	$ (94,384)
Net income (loss) per share of common stock:
Basic (in dollars per share)	$ 0.17	$ (10.64)	$ (2.30)	$ (22.80)
Diluted (in dollars per share)	$ (0.42)	$ (10.64)	$ (2.30)	$ (22.80)
Weighted average shares used in per share computation:
Basic (in shares)	212,071	4,406	89,233	4,139
Diluted (in shares)	236,965	4,406	89,233	4,139
Product
Total revenue	$ 59,907	$ 46,142	$ 167,401	$ 137,253
Total cost of goods sold	57,034	43,949	162,513	130,505
Parts and other service
Total revenue	2,034	1,395	7,048	5,543
Total cost of goods sold	$ 2,244	$ 1,679	$ 7,089	$ 5,862

CONDENSED CONSOLIDATED STATEM_2

CONDENSED CONSOLIDATED STATEMENTS OF STOCKHOLDERS’ EQUITY (UNAUDITED) - USD ($) shares in Thousands, $ in Thousands	Total	Legacy warrants	Convertible Preferred Stock	Common Stock	Additional Paid-in Capital	Additional Paid-in CapitalLegacy warrants	Accumulated Deficit
Beginning balance (in shares) at Dec. 31, 2019			115,136	3,927
Beginning balance at Dec. 31, 2019	$ 186,979		$ 13	$ 0	$ 668,178		$ (481,212)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs (in shares)				724
Issuance of stock, net of costs	1,595			$ 1	1,594
Stock-based compensation	7,551				7,551
Net loss	(94,384)						(94,384)
Ending balance (in shares) at Sep. 30, 2020			115,136	4,651
Ending balance at Sep. 30, 2020	101,741		$ 13	$ 1	677,323		(575,596)
Beginning balance (in shares) at Jun. 30, 2020			115,136	4,222
Beginning balance at Jun. 30, 2020	145,068		$ 13	$ 0	673,791		(528,736)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of stock, net of costs (in shares)				429
Issuance of stock, net of costs	853			$ 1	852
Stock-based compensation	2,680				2,680
Net loss	(46,860)						(46,860)
Ending balance (in shares) at Sep. 30, 2020			115,136	4,651
Ending balance at Sep. 30, 2020	101,741		$ 13	$ 1	677,323		(575,596)
Beginning balance (in shares) at Dec. 31, 2020			115,136	5,678
Beginning balance at Dec. 31, 2020	74,466		$ 13	$ 1	682,671		(608,219)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Conversion of convertible preferred stock into common stock in connection with the reverse recapitalization (in shares)			(115,136)	115,576
Conversion of convertible preferred stock into common stock in connection with the reverse recapitalization	0		$ (13)	$ 11	2
Conversion of Convertible Notes into common stock (in shares)				7,424
Conversion of Convertible Notes into common stock	48,781			$ 1	48,780
Issuance of common stock upon the reverse recapitalization, net of issuance costs (in shares)				76,172
Issuance of common stock upon the reverse recapitalization, net of issuance costs	502,315			$ 8	502,307
Issuance of stock upon exercise of options	5,468			$ 3,241	5,468
Reclassification of derivative liability upon the reverse recapitalization	182,554				182,554
Reclassification of warrant liability upon reverse recapitalization		$ 87,016				$ 87,016
Issuance of Earnout Shares, net of repurchase (in shares)				4,736
Issuance of Earnout Shares, net of repurchase	(634)				(634)
Stock-based compensation	11,265				11,265
Net loss	(204,868)						(204,868)
Ending balance (in shares) at Sep. 30, 2021			0	212,827
Ending balance at Sep. 30, 2021	706,363		$ 0	$ 21	1,519,429		(813,087)
Beginning balance (in shares) at Jun. 30, 2021			0	207,621
Beginning balance at Jun. 30, 2021	665,944		$ 0	$ 21	1,515,331		(849,408)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Issuance of common stock upon the reverse recapitalization, net of issuance costs	(112)				(112)
Issuance of common stock upon exercise of options and warrants (in shares)				470
Issuance of stock upon exercise of options	1,666				1,666
Issuance of Earnout Shares, net of repurchase (in shares)				4,736
Issuance of Earnout Shares, net of repurchase	(634)				(634)
Stock-based compensation	3,178				3,178
Net loss	36,321						36,321
Ending balance (in shares) at Sep. 30, 2021			0	212,827
Ending balance at Sep. 30, 2021	$ 706,363		$ 0	$ 21	$ 1,519,429		$ (813,087)

CONDENSED CONSOLIDATED STATEM_3

CONDENSED CONSOLIDATED STATEMENTS OF CASH FLOWS (UNAUDITED) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash flows from operating activities:
Net loss	$ (204,868)	$ (94,384)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	11,675	11,493
Loss (gain) on disposal of fixed assets	411	(6)
Stock-based compensation	11,265	7,551
Amortization of debt discount and issuance costs	31,519	2,342
Accretion of debt end of term charge and PIK interest	6,375	1,219
Loss on valuation of derivative and warrant liabilities	72,913	19,061
Others	991	(134)
Changes in operating assets and liabilities:
Accounts receivable	(8,223)	(2,608)
Inventory	(9,622)	(4,923)
Prepaid expenses and other current assets	(5,231)	(2,610)
Deferred cost of goods sold	175	(733)
Operating lease right-of-use assets and liabilities	(84)	86
Other assets	(1,785)	(1,315)
Accounts payable and accrued liabilities	21,977	(4,059)
Deferred revenue, current and non-current	(673)	5,264
Other non-current liabilities	934	4,164
Net cash used in operating activities	(72,251)	(59,592)
Cash flows from investing activities
Purchase of investments	(472,953)	(64,972)
Proceeds from maturities and sales of investments	94,000	40,000
Purchase of property and equipment	(12,912)	(19,769)
Net cash used in investing activities	(391,865)	(44,741)
Cash flows from financing activities:
Proceeds from reverse recapitalization, net of transaction costs	644,809	0
Payment of tax withholding obligations on Earnout Shares	(634)	0
Proceeds from debt, net of issuance costs	0	224,047
Repayment of debt and prepayment penalty	(17,083)	(22,787)
Repayment of finance obligation	(362)	(365)
Proceeds from government grants	1,323	275
Proceeds from exercise of stock options	5,468	1,550
Net cash provided by financing activities	633,521	202,720
Net increase in cash and cash equivalents, and restricted cash	169,405	98,387
Cash and cash equivalents, and restricted cash at the beginning of period	123,697	53,649
Cash and cash equivalents, and restricted cash at the end of period	293,102	152,036
Supplemental disclosures of cash flow information:
Cash paid for interest	4,912	2,049
Cash paid for income taxes	0	0
Non-cash investing and financing activity:
Assets acquired through accounts payable and accrued liabilities	1,532	3,373
Non-cash transfer of leased assets to inventory	743	635
Reclassification of Convertible Notes warrants liability upon exercise	17,696	0
Conversion of Convertible Notes into common stock	48,607	0
Reclassification of remaining Convertible Notes warrants liability upon the reverse recapitalization	69,320	0
Reclassification of derivative liability upon the reverse recapitalization	182,554	0
Conversion of convertible preferred stock into common stock	$ 627,315	$ 0

Summary of Significant Accounti

Summary of Significant Accounting Policies	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Summary of Significant Accounting Policies Organization and Description of Business Proterra Inc (“Proterra”), formerly known as ArcLight Clean Transition Corp. (“ArcLight”), is a leading developer and producer of electric vehicle technology for commercial applications. Proterra designs, develops, manufactures, and sells electric transit buses as an original equipment manufacturer for North American public transit agencies, airports, universities, and other commercial transit fleets. It also designs, develops, manufactures, sells, and integrates proprietary battery systems and electrification solutions for global commercial vehicle manufacturers. Additionally, Proterra provides fleet-scale, high-power charging infrastructure solutions for its customers. On June 11, 2021, ArcLight filed a notice of deregistration with the Cayman Islands Registrar of Companies, and filed a certificate of incorporation and a certificate of corporate domestication with the Secretary of State of the State of Delaware, under which ArcLight was domesticated and continued as a Delaware corporation. On June 14, 2021 (the “Closing Date”), ArcLight consummated a merger with Phoenix Merger Sub, Inc., a Delaware corporation and a wholly-owned subsidiary of ArcLight (“Phoenix Merger Sub”), and Proterra Inc, a Delaware corporation (“Legacy Proterra”) with Legacy Proterra surviving as the surviving company and as a wholly-owned subsidiary of ArcLight (the “Merger” and, collectively with the other transactions described in the Agreement and Plan of Merger (the “Merger Agreement”), the “Business Combination”). In connection with the Business Combination, Legacy Proterra changed its name to “Proterra Operating Company, Inc.” and ArcLight changed its name to “Proterra Inc”. The Merger was accounted for as a reverse merger and a recapitalization with Legacy Proterra being the accounting acquirer. Accordingly, all historical financial information presented in the unaudited condensed consolidated financial statements of Proterra represents the accounts of Legacy Proterra and its wholly owned subsidiaries as if Legacy Proterra is the predecessor to Proterra. The shares and net loss per common share, prior to the Merger, have been retroactively restated as shares reflecting the exchange ratio established in the Merger (0.8925 shares of Legacy Proterra common stock for 1 share of Proterra common stock) (the “Exchange Ratio”). Unless otherwise specified or unless the context otherwise requires, references in these notes to the “Company” refer to Legacy Proterra prior to the Business Combination and to Proterra following the Business Combination. Prior to the closing of the Business Combination (the “Closing”), ArcLight’s Class A ordinary shares and public warrants were listed on the Nasdaq Capital Market under the symbols “ACTC” and “ACTCW,” respectively. Proterra’s common stock is currently listed on the Nasdaq Global Select Market under the symbol “PTRA”. Please refer to Note 3 “Reverse Recapitalization” for further details of the Merger. The Company’s public warrants were previously listed on the Nasdaq Global Select Market under the symbol “PTRAW.” On October 29, 2021, the Company redeemed its remaining outstanding public warrants at a redemption price of $0.10 per public warrant. See Note 14, Subsequent events. The Company has incurred net losses and negative cash flows from operations since inception. As of September 30, 2021, the Company has an accumulated deficit of $813.1 million. The Company has $727.5 million of cash and cash equivalents and short-term investments as of September 30, 2021. The Company has funded operations primarily through a combination of equity and debt financing. Management believes that the Company’s currently available resources will be sufficient to fund its cash requirements for at least the next twelve months. Basis of Presentation The unaudited condensed consolidated financial statements and accompanying notes have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and the rules and regulations of the U.S. Securities and Exchange Commission (the “SEC”). The Company’s condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated upon consolidation. Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2020 and the related notes incorporated by referenced in the Company’s Current Report on Form 8-K, filed with SEC on June 17, 2021, which provides a more complete discussion of the Company’s accounting policies and certain other information. The information as of December 31, 2020 and 2019 was derived from the Company’s audited financial statements. The condensed consolidated financial statements were prepared on the same basis as the audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for a fair presentation of the Company’s financial position as of September 30, 2021 and the results of operations and cash flows for the three and nine months ended September 30, 2021 and 2020. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. There have been no changes to the Company’s significant accounting policies described in the annual financial statements for the year ended December 31, 2020, except for the new accounting policies adopted during the three months ended June 30, 2021 related to public warrants and private placement warrants described below, that have had a material impact on the Company’s condensed consolidated financial statements and related notes. The Company has not experienced any significant impact to estimates or assumptions as a result of the COVID-19 pandemic. However, there have been some impacts, specifically as it relates to parts, logistics and overall transit order timing. The Company will continue to monitor impacts of the pandemic on an ongoing basis. While the COVID-19 pandemic has not had a material adverse impact on the Company’s financial condition and results of operations to date, the future impact of the COVID-19 pandemic on the Company’s operational and financial performance will depend on certain developments, including the duration of the pandemic and spread of COVID-19 (including the variant strains of the virus), impact on the Company’s customers and effect on the Company’s suppliers, all of which are uncertain and cannot be predicted. Segments The Company operates in the United States and has sales to the European Union, Canada, Australia and Japan. Revenue disaggregated by geography, based on the addresses of our customers, consists of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 United States 59,482 42,709 163,972 104,612 Rest of World 2,459 4,828 10,477 38,184 61,941 47,537 174,449 142,796 The revenue generated outside of the United States in 2020 was mainly from sales to customers in Canada. The Company’s chief operating decision maker is its Chief Executive Officer (CEO), who reviews financial information presented at the entity level. Accordingly, the Company has determined that it has a single reportable segment. Foreign Currency Transactions Net gains or losses resulting from foreign exchange transactions were not material for all periods presented. Accounts Receivable and Allowance for Credit Losses Accounts receivable are recorded at the invoiced amount and do not bear interest. The Company determines the allowance for credit losses based on historical write-off experience, an analysis of the aging of outstanding receivables, customer payment patterns and expectations of changes in macroeconomic conditions that may affect the collectability of outstanding receivables. The allowance for credit losses was not material as of September 30, 2021 and December 31, 2020. Short-Term Investments The Company’s primary objectives for investment activities are to preserve principal, provide liquidity, and maximize income without significantly increasing risk. The Company’s short-term investments were primarily comprised of U.S. Treasury and corporate debt securities, and classified as available-for-sale at the time of purchase because it is intended that these investments are available for current operations. Investments are reported at fair value and are subject to periodic impairment review. Unrealized gains and losses related to changes in the fair value of these securities will be recognized in accumulated other comprehensive loss. The ultimate value realized on these securities is subject to market price volatility until they are sold. Realized gains or losses from short-term investments are recorded in other expense (income), net. Restricted Cash The Company maintains certain cash amounts restricted as to withdrawal or use. The restricted cash is primarily collateral for performance bonds issued to certain customers. The collateral is provided in the form of a cash deposit to either support the bond directly or to collateralize a letter of credit that supports the performance bonds. Restricted cash was $12.6 million and $13.0 million as of September 30, 2021 and December 31, 2020, respectively. Credit Risk and Concentration The Company’s financial instruments that are potentially subject to concentrations of credit risk consist primarily of cash, cash equivalents, restricted cash, short-term investments, and accounts receivable. Cash and cash equivalents and short-term investments are maintained primarily at a financial institution as of September 30, 2021, and deposits exceed federally insured limits. Risks associated with cash and cash equivalents, and short-term investments are mitigated by banking with creditworthy financial institutions. The Company has not experienced any losses on its deposits of cash and cash equivalents or its short-term investments. Cash equivalents and short-term investments consist of short-term money market funds, corporate debt securities, and debt securities issued by the U.S. Treasury, which are deposited with reputable financial institutions. The Company’s cash management and investment policy limits investment instruments to investment-grade securities with the objective to preserve capital and to maintain liquidity until the funds can be used in business operations. Accounts receivable are typically unsecured and are generally derived from revenue earned from transit agencies, universities and airports in North America and global commercial vehicle manufacturers in North America, the European Union, Australia and Japan. The Company periodically evaluates the collectability of its accounts receivable and provides an allowance for potential credit losses as necessary. Given the large order value for customers and the relatively low number of customers, revenue and accounts receivable have typically been concentrated with a limited number of customers. Revenue Accounts Receivable Three Months Ended September 30, Nine Months Ended September 30, September 30, December 31, 2021 2020 2021 2020 2021 2020 Number of customers accounted for 10% or more* 2 4 — 4 2 2 __________________ * One customer accounted for 33% of accounts receivable, net as of December 31, 2020. No other individual customer accounted for more than 20% of the Company's revenue for the three and nine months ended September 30, 2021 and 2020, or accounts receivable as of September 30, 2021 and December 31, 2020. Single source suppliers provide the Company with a number of components that are required for manufacturing of its current products. In other instances, although there may be multiple suppliers available, many of the components are purchased from a single source. If these single source suppliers fail to meet the Company’s requirements on a timely basis at competitive prices, the Company could suffer manufacturing delays, a possible loss of revenue, or incur higher cost of sales, any of which could adversely impact the Company’s operating results. Fair Value of Financial Instruments The carrying value of the Company’s financial instruments, including cash and cash equivalents, accounts receivable, short-term investments, accounts payable, and accrued and other current liabilities, approximates fair value due to the short period of time to maturity, receipt, or payment. The carrying amount of the Company’s debt, except for Convertible Notes (as defined below), approximates its fair value as the stated interest rates approximate market rates currently available to the Company. In August 2020, the Company issued Secured Convertible Promissory Notes (the “Convertible Notes”) that, prior to the Closing, contained embedded features subject to derivative accounting. These embedded features were composed of conversion options that had the economic characteristics of a contingent early redemption feature settled in a variable number of shares of the Company’s stock. These conversion options were bifurcated and accounted for as a derivative liability separately from the host debt instrument. Embedded derivatives were recognized as a derivative liability on the balance sheet. The derivative liability was measured at fair value and subject to remeasurement at each balance sheet date. Upon the consummation of the Merger, the embedded conversion features associated with the Convertible Notes no longer qualify for derivative accounting after the conversion price became fixed. The carrying amount of the embedded derivative, the fair value as of the date of the Closing, was reclassified to stockholders’ equity in accordance with Topic 815, Derivatives and Hedging. The warrants issued in connection with the Convertible Notes were, prior to the Closing, classified as a liability (“legacy Proterra warrant liability”) because they could become exercisable into common stock upon a Qualified Initial Public Offering (“QIPO”) or into convertible preferred stock after 5 years from issuance date in the event that there was no QIPO during such period. Such warrants were measured at fair value, subject to remeasurement at each balance sheet date. Upon exercise of the warrants to common stock within 5 years from issuance date, the carrying amount of the warrant liability would be reclassified to stockholders’ equity. Upon the consummation of the Merger, the stock issuable upon exercise of the warrants is common stock, with no possibility to convert to Legacy Proterra convertible preferred stock. As a result, the carrying amount of the warrant liability was reclassified to stockholders’ equity. In connection with ArcLight’s initial public offering in September 2020, 21,425,000 warrants to purchase ArcLight ordinary shares were issued, including 13,875,000 public warrants and 7,550,000 private placement warrants. These warrants were classified as liabilities as they did not meet the requirements for equity classification under Topic 815, Derivatives and Hedging. These warrants were continually measured at fair value, subject to remeasurement at each balance sheet date. Inventories Inventories are recorded at the lower of cost and net realizable value using the first-in, first-out method. Inventory costs consist primarily of the cost of materials, manufacturing support costs, including labor and factory overhead associated with such production, and shipping costs. The costs of vehicles, charger equipment or prototype products delivered to customers that have not yet met revenue recognition criteria are also included in inventories. The Company assesses the valuation of inventory and periodically records a provision to adjust inventory to its estimated net realizable value, including when the Company determines inventory to be obsolete or in excess of anticipated demand. Once inventory has been written-off or written-down, it creates a new cost basis for the inventory that is not subsequently written-up. Impairment of Long-Lived Assets The Company evaluates the recoverability of property, plant, and equipment and right-of-use assets for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets are expected to generate. If such review indicates that the carrying amount of long-lived assets is not recoverable, the carrying amount of such assets is reduced to fair value. In addition to the recoverability assessment, the Company periodically reviews the remaining estimated useful lives of property, plant, and equipment. If the estimated useful life assumption for any asset is reduced, the remaining net book value is depreciated over the revised estimated useful life. The Company reviews long-lived assets for impairment at the lowest level for which separate cash flows can be identified. No impairment charge was recognized in the three or six months ended September 30, 2021 and 2020. Deferred Revenue Deferred revenue consists of billings or payments received in advance of revenue recognition that are recognized as revenue once the revenue recognition criteria are met. In some instances, progress billings are issued upon meeting certain milestones stated in the contracts. Accordingly, the deferred revenue balance does not represent the total contract value of non-cancelable arrangements. Invoices are typically due within 30 to 40 days. The changes in deferred revenue consisted of the following (in thousands): Deferred revenue as of December 31, 2020 $ 28,221 Revenue recognized from beginning balance during the nine months ended September 30, 2021 (11,774) Deferred revenue added during the nine months ended September 30, 2021 11,101 Deferred revenue as of September 30, 2021 $ 27,548 The current portion of deferred revenue represents the amount that is expected to be recognized as revenue within one year from the balance sheet date. Revenue Recognition The Company derives revenue primarily from the sale of vehicles and charging systems, the installation of charging systems, the sale of battery systems and powertrain components to other vehicle manufacturers, as well as the sale of spare parts and other services provided to customers. Product revenue consists of revenue earned from vehicles and charging systems, battery systems and powertrain components, installation of charging systems, and revenue from leased vehicles, charging systems, and batteries under operating leases. Leasing revenue recognized over time was approximately $0.5 million in each of the three months ended September 30, 2021 and 2020, and $1.6 million and $1.8 million in the nine months ended September 30, 2021 and 2020, respectively. Parts and other service revenue includes revenue earned from spare parts, the design and development of battery systems and drive systems for other vehicle manufacturers, and extended warranties. Goods and services that are promised in the Company’s contracts include vehicles, charging systems, battery systems and powertrain components to other vehicle manufacturers, installation of charging systems, spare parts, and extended warranty. The Company assesses the products and services promised in contracts at contract inception, and identifies performance obligations for each promise to transfer to the customer a product or service that is distinct. If a product or service is separately identifiable from other items in the bundled arrangement and a customer can benefit from the product or service on its own or with other resources that are readily available to the customer, then such product or service is considered distinct. Customer contracts typically have multiple performance obligations. Generally, the Company’s goods and services are considered separate performance obligations. Development services are typically sold on a stand-alone basis and are not bundled with other goods or services. The transaction price of the contract is allocated to each performance obligation in a manner depicting the amount of consideration to which the Company expects to be entitled in exchange for transferring the goods or services to the customer (the “allocation objective”). If the allocation objective is met at contractual prices, no further allocations are made. Otherwise, the Company allocates the transaction price to each performance obligation identified in the contract on a relative standalone selling price basis. To determine the standalone selling price of its promised products or services, the Company conducts an analysis to determine whether its products or services have an observable standalone selling price. In determining the observable standalone selling price, the Company requires that a substantial majority of the standalone selling prices for a product or service fall within a reasonably narrow range. If there is no directly observable standalone selling price for a particular product or service, then the Company estimates a standalone selling price by using the estimated cost plus margin or by reviewing external and internal market factors including, but not limited to, pricing practices including historical discounting, major service groups, and the geographies in which the Company offers products and services. The Company recognizes revenue when or as it satisfies a performance obligation by transferring control of a product or service to a customer. Revenue from product sales is recognized when control of the underlying performance obligations is transferred to the customer. Revenue from vehicles and charging systems, and installation of charging systems is typically recognized upon acceptance by the customer. Under certain contract arrangements, the control of the performance obligations related to the charging systems is transferred over time, and the associated revenue is recognized over the installation period using an input measure based on costs incurred to date relative to total estimated costs to completion. Spare parts revenue is recognized upon shipment. Extended warranty revenue is recognized over the life of the extended warranty using the time elapsed method. Development service contracts typically include the delivery of prototype products to customers. The performance obligation associated with the development of prototype products as well as battery systems and powertrain components to other vehicle manufacturers, is satisfied at a point in time, typically upon shipping. Revenue derived from performance obligations satisfied over time from charging systems and installation was $0.2 million and $1.1 million for the three months ended September 30, 2021 and 2020, respectively, and $5.3 million and $2.3 million for the nine months ended September 30, 2021 and 2020, respectively. Extended warranty revenue is not material to date. As of September 30, 2021 and December 31, 2020, the contract assets balance was $1.3 million and $2.8 million, respectively. The contract assets are expected to be billed within the next twelve months and are recorded in prepaid expenses and other current assets on the balance sheets. As of September 30, 2021, the amount of remaining performance obligations that have not been recognized as revenue was $305.9 million, of which 80% were expected to be recognized as revenue over the next 12 months and the remainder thereafter. This amount excludes the value of remaining performance obligations for contracts with an original expected length of one year or less. While our business has historically been centered on the development and sale of electric transit buses, the increased significance of revenue from Proterra Powered has caused the Company to consider reorganizing into two business units with three business lines, each of which addresses a critical component of the commercial vehicle electrification value proposition in a complementary and self-reinforcing manner: • Proterra Transit designs, develops, manufactures, and sells electric transit buses as an original equipment manufacturer (“OEM”) for North American public transit agencies, airports, universities, and other commercial transit fleets. • Proterra Powered & Energy includes Proterra Powered, which designs, develops, manufactures, sells, and integrates proprietary battery systems and electrification solutions into vehicles for global commercial vehicle OEMs, and Proterra Energy, which provides turnkey fleet-scale, high-power charging solutions and software services, ranging from fleet and energy management software-as-a-service, to fleet planning, hardware, infrastructure, installation, utility engagement, and charging optimization. The revenue of business units are as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Proterra Transit $ 50,175 $ 30,026 $ 140,187 $ 112,870 Proterra Powered & Energy 11,766 17,511 34,262 29,926 Total $ 61,941 $ 47,537 $ 174,449 $ 142,796 Lease Arrangements The Company offers customers leasing alternatives outside of the standard sales contracts for vehicles, charging equipment and batteries used in the vehicles. The leasing arrangements are typically bundled together with the sales contracts. The Company assessed the nature of the bundled arrangements under the revenue accounting standard. For arrangements that contain a lease, the Company determines the classification of the lease in accordance with Topic 842, Leases. A lease arrangement that transfers substantially all of the benefits and risks incident to ownership of the products is classified as a sales-type lease based on the criteria established by the accounting standard; otherwise the lease is classified as an operating lease. For sales-type leases, product revenue is recognized upon customer acceptance of the underlying leased assets. The current portion of net investment in sales-type leases is recorded in Accounts Receivable, and the non-current portion is recorded in Other Assets on the Company’s balance sheets. The discounted unguaranteed residual value of underlying leased assets is not material to the net investment in lease balance. For operating leases, the leasing revenue is recognized on a straight-line basis over the lease term, which is commenced upon customer acceptance. The Company monitors the performance of customers who have leased batteries and are subject to ongoing payments. No allowance was recorded for the receivables under the leasing arrangements. Product Warranties The Company provides a limited warranty to customers on vehicles, charging systems, and battery systems. The limited warranty ranges from one Warranty expense is recorded as a component of cost of goods sold. Accrued warranty activity consisted of the following (in thousands): Nine Months Ended September 30, 2021 Warranty reserve - beginning of period $ 18,582 Warranty costs incurred (5,650) Net changes in liability for pre-existing warranties, including expirations (1,663) Provision for warranty 10,243 Warranty reserve - end of period $ 21,512

Adoption of New Accounting Stan

Adoption of New Accounting Standards	9 Months Ended
	Sep. 30, 2021
Accounting Changes and Error Corrections [Abstract]
Adoption of New Accounting Standards	Adoption of New Accounting Standards ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . This standard simplifies the accounting for income taxes, eliminates certain exceptions within Topic 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. The Company adopted this standard on January 1, 2021, and it had no material impact on the consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity . This standard simplifies the accounting for convertible instruments by removing certain separation models in ASC 470- 20, Debt—Debt with Conversion and Other Options , for convertible instruments. This standard updates the guidance on certain embedded conversion features that are not required to be accounted for as derivatives under Topic 815, Derivatives and Hedging , or that do not result in substantial premiums accounted for as paid-in capital, such that those features are no longer required to be separated from the host contract. The convertible debt instruments will be accounted for as a single liability measured at amortized cost. This will also result in the interest expense recognized for convertible debt instruments to be typically closer to the coupon interest rate when applying the guidance in Topic 835, Interest . Further, this standard made amendments to the EPS guidance in Topic 260 for convertible instruments, the most significant impact of which is requiring the use of the if-converted method for diluted earnings per share calculation, and no longer allowing the net share settlement method. This standard also made revisions to Topic 815-40, which provides guidance on how an entity must determine whether a contract qualifies for a scope exception from derivative accounting. The amendments to Topic 815-40 change the scope of contracts that are recognized as assets or liabilities. This standard is effective for interim and annual periods beginning after December 15, 2021, with early adoption permitted after December 15, 2020. Adoption of this standard can either be on a modified

Reverse Recapitalization

Reverse Recapitalization	9 Months Ended
	Sep. 30, 2021
Reverse Recapitalization [Abstract]
Reverse Recapitalization	Reverse Recapitalization On June 14, 2021, Phoenix Merger Sub merged with Legacy Proterra, with Legacy Proterra surviving as a wholly-owned subsidiary of ArcLight. In connection with the Business Combination, Legacy Proterra changed its name to “Proterra Operating Company, Inc.” and ArcLight changed its name to “Proterra Inc”. The following transactions occurred upon the Closing: • each share of outstanding Legacy Proterra convertible preferred stock was converted into shares of Proterra common stock in accordance with the applicable conversion ratio immediately prior to the effective time, and each share of Legacy Proterra common stock (including shares issued upon conversion of Legacy Proterra convertible preferred stock and warrants net exercised upon Closing) was converted into shares of common stock after giving effect of the Exchange Ratio of 0.8925 and resulting in the issuance of 123,752,882 shares of common stock; • certain holders of Convertible Notes with an original aggregate principal amounts of $46.5 million elected to convert their outstanding Convertible Notes balances including accrued PIK interest and cash interest at the Closing resulting in the issuance of 7.4 million shares of common stock; • each outstanding Legacy Proterra option was converted into an option to purchase shares of Proterra common stock by multiplying the number of underlying shares by the Exchange Ratio, rounded down to the nearest whole share, resulting in such options being exercisable to purchase for an aggregate of 22,532,619 shares of Proterra common stock; the exercise price of each converted option was determined by dividing the per share exercise price of the respective Legacy Proterra options by the Exchange Ratio of 0.8925, rounded up to the nearest whole cent; • each outstanding Legacy Proterra warrant to purchase Legacy Proterra common stock and convertible preferred stock was converted into a warrant to purchase shares of Proterra common stock by multiplying the number of underlying shares by the Exchange Ratio, rounded down to the nearest whole share, resulting in such warrants being exercisable to purchase an aggregate of 3,504,523 shares of Proterra common stock; the exercise price of each converted warrant will be determined by dividing the per share exercise price of the respective Legacy Proterra warrant by the Exchange Ratio of 0.8925, rounded up to the nearest whole cent; • each outstanding Convertible Note that was not optionally converted in connection with the Closing remained outstanding and became convertible into shares of Proterra common stock in accordance with the terms of such Convertible Notes. • 15,172 public shares were redeemed by ArcLight shareholders, and an aggregate of $0.2 million was paid from the trust account to these redeeming holders; and each share of ArcLight Class A and Class B ordinary shares was converted into the right to receive one share of Proterra’s common stock resulting in the issuance of 34,671,900 shares of common stock; • pursuant to the subscription agreements between ArcLight and certain investors (the “PIPE Investors”), the PIPE Investors purchased 41.5 million shares of Proterra common stock at a purchase price of $10.00 per share for aggregate gross proceeds of $415.0 million (the “PIPE Financing”); • each ArcLight warrant outstanding immediately prior to the consummation was converted into a warrant exercisable into an equivalent number of shares of Proterra common stock, resulting in such warrants being exercisable for an aggregate of 21,424,994 shares of Proterra common stock; and • the 669,375 shares of Proterra common stock underlying certain Milestone Options (as defined below) fully vested upon the Closing. Upon the occurrence of any of the following events during the first five years following the Closing of the Merger (“earnout period”), up to an additional 22,809,500 shares of Proterra common stock (the “Earnout Stock”) may be issued to former holders of Legacy Proterra convertible preferred stock, common stock, warrants, vested options and Convertible Notes as of immediately prior to the closing of the Merger, as follows: a. 21.0526% of the Earnout Stock if over any 20 trading days within any 30 trading day period, the volume-weighted average price (“VWAP”) of the Proterra common stock is greater than or equal to $15.00 per share or there occurs any transaction resulting in a change in control with a valuation of the Proterra common stock that is greater than or equal to $15.00 per share (the “First Earnout Shares”); b. an additional 26.3158% of the Earnout Stock if over any 20 trading days within any 30 trading day period, the VWAP of the Proterra common stock is greater than or equal to $20.00 per share or there occurs any transaction resulting in a change in control with a valuation of the Proterra common stock that is greater than or equal to $20.00 per share; c. an additional 26.3158% of the Earnout Stock if over any 20 trading days within any 30 trading day period, the VWAP of the Proterra common stock is greater than or equal to $25.00 per share or there occurs any transaction resulting in a change in control with a valuation of the Proterra common stock that is greater than or equal to $25.00 per share; d. an additional 26.3158% of the Earnout Stock if over any 20 trading days within any 30 trading day period, the VWAP of the Proterra common stock is greater than or equal to $30.00 per share or there occurs any transaction resulting in a change in control with a valuation of the Proterra common stock that is greater than or equal to $30.00 per share; Pursuant to a letter agreement (the “Sponsor Letter Agreement”) with ArcLight CTC Holdings, L.P. (the “Sponsor”), 10% of the Proterra common stock received by the Sponsor upon consummation of the Merger in exchange for its outstanding shares of ArcLight Class B ordinary shares, excluding 140,000 shares owned by the ArcLight board of directors, was subject to vesting and forfeiture (the “Sponsor Earnout Stock”). Such shares of Sponsor Earnout Stock would vest if over any 20 trading days within any 30 trading day period during the five-year earnout period, the VWAP of the Proterra common stock was greater than or equal to $15.00 per share or there occurred any transaction resulting in a change in control with a valuation of the Proterra common stock that is greater than or equal to $15.00 per share. The Earnout Stock and Sponsor Earnout Stock are equity-classified instruments under U.S. GAAP. The number of shares of Proterra common stock issued immediately following the consummation of the Merger was (in thousands): Shares Ordinary shares Class A of ArcLight, outstanding prior to Merger 27,750 Less redemption of ArcLight shares (15) Sponsor 6,257 Sponsor Earnout Stock 680 Common stock of ArcLight 34,672 PIPE Investors 41,500 Legacy Proterra shares 131,176 Total shares of common stock immediately after Merger 207,348 Immediately after the Merger, Proterra is authorized to issue 510.0 million shares, with a par value of $0.0001 per share. As of the Closing, the authorized shares consisted of 500.0 million shares of common stock and 10.0 million shares of preferred stock, and there were 207.3 million shares of common stock issued and outstanding, and no shares of preferred stock issued and outstanding. In addition, as of the Closing, there were 24.9 million warrants issued and outstanding, including 13.9 million public warrants, 7.6 million private placement warrants, and 3.5 million Legacy Proterra warrants. As of the Closing, a total of 82.3 million shares were reserved for future issuance upon the exercise of stock options, warrants and the issuance of Earnout Stock, of which 10.4 million shares were reserved for issuance under Proterra’s 2021 Equity Incentive Plan, 22.5 million shares were reserved under Legacy Proterra’s 2010 Equity Incentive Plan and 1.6 million shares reserved under Proterra’s 2021 Employee Stock Purchase Plan. The Merger has been accounted for as a reverse merger and a recapitalization under U.S. GAAP with Legacy Proterra being the accounting acquirer, based on evaluation of the following facts and circumstances: • Legacy Proterra’s stockholders have a majority of the voting power of Proterra following the Merger; • Legacy Proterra has initially designated a majority of the board of directors of Proterra; • Legacy Proterra’s management comprise the management of Proterra; • Legacy Proterra comprises the ongoing operations of Proterra; • Legacy Proterra is the larger entity based on historical revenues and business operations; and • Proterra has assumed Legacy Proterra’s name. Under this method of accounting, ArcLight is treated as the “acquired” company for accounting and financial reporting purposes. Accordingly, for accounting purposes, this merger transaction is treated as the equivalent of Legacy Proterra issuing equity for the net assets of ArcLight, accompanied by a recapitalization. The net assets of ArcLight have been stated at historical cost, with no goodwill or other intangible assets recorded. The Company received aggregate cash proceeds of $649.3 million at the Closing, net of $13.8 million of PIPE Financing fees, $18.5 million of other transaction costs paid at Closing, $9.7 million of ArcLight IPO deferred underwriting fees payable, $1.3 million of other ArcLight’s accrued expenses, and $0.1 million of ArcLight’s related party payable. The unbilled ArcLight expenses incurred prior to the Closing were paid from the cash proceeds received by the Company. The transaction costs including advisory, legal and other professional services directly related to the Merger were recorded in the additional paid-in capital in the balance sheet to offset against proceeds. The deferred transaction costs of approximately $2.9 million paid by the Company prior to the Closing were recorded to the additional paid-in capital and classified as financing activities in the statement of cash flow for the nine months ended September 30, 2021. In July 2021, the conditions for the issuance of the First Earnout Shares and the vesting of the Sponsor Earnout Stock were satisfied, resulting in an aggregate of 4,800,563 shares of common stock being issued and the 679,750 shares of Sponsor Earnout Stock fully vesting.

Fair Value of Financial Instrum

Fair Value of Financial Instruments	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Fair Value of Financial Instruments	Fair Value of Financial Instruments The Company measures certain financial assets and liabilities at fair value. Fair value is determined based on the exit price that would be received from selling an asset or paid to transfer a liability in an orderly transaction between market participants at the measurement date. Fair value is estimated by applying the following hierarchy: Level 1 – Quoted prices in active markets for identical assets or liabilities; Level 2 – Observable inputs other than quoted prices in active markets for identical assets and liabilities, quoted prices for identical or similar assets or liabilities in inactive markets, or other inputs that are observable or can be corroborated by observable market data for substantially the full term of the assets or liabilities; and Level 3 – Inputs that are generally unobservable and typically reflect management’s estimate of assumptions that market participants would use in pricing the asset or liability. Financial assets measured at fair value on a recurring basis using the above input categories were as follows (in thousands): Pricing Category Fair Value at September 30, 2021 December 31, 2020 Assets: Cash equivalents and marketable securities: Money market funds Level 1 $ 12,620 $ 744 U.S. Treasury securities Level 1 199,920 64,997 Short-term investments: U.S. Treasury securities Level 1 261,068 68,990 Corporate debt securities Level 1 185,883 — Total $ 659,491 $ 134,731 Liabilities: Other non-current liabilities Derivative liability Level 3 $ — $ 70,870 Legacy Proterra warrant liability Level 3 — 39,670 Public warrant liability Level 1 36,352 — Private placement warrant liability Level 2 19,781 — Total $ 56,133 $ 110,540 As of September 30, 2021 and December 31, 2020, short-term investments were primarily comprised of U.S. Treasury and corporate debt securities. The unrealized gain/losses related to fixed income debt securities were immaterial and primarily due to changes in interest rates, which are temporary in nature. The contractual maturities of short-term investments are as follows (in thousands): September 30, 2021 December 31, 2020 Due within one year $ 296,934 $ 68,990 Due after one year to two years 150,017 — Total $ 446,951 $ 68,990 In August 2020, the Company issued Convertible Notes that, prior to the Closing, contained embedded features subject to derivative accounting. Refer to Note 6, Debt, for additional information on the Convertible Notes. The embedded derivatives were recognized as a derivative liability on the balance sheet, and were measured at fair value, subject to remeasurement at each balance sheet date. The fair value of derivative liability was measured as the difference between the estimated value of the Convertible Notes with and without such conversion features utilizing a Monte Carlo simulation pricing model. The warrants issued in connection with the Convertible Notes were, prior to the Closing, classified as a liability because they could become exercisable into common stock upon a QIPO or into convertible preferred stock after five years from issuance date in the event that there was no QIPO during such period. Such warrants were measured at fair value, subject to remeasurement at each balance sheet date. The fair value of the warrant liability was measured using a Monte Carlo Simulation pricing model. The fair value of the Convertible Notes was $303.4 million as of September 30, 2021. The carrying value of the Convertible Notes of $95.9 million, net of $65.6 million unamortized debt discount and issuance costs, as of September 30, 2021, was recorded in Debt, non-current on the balance sheets. The public warrants and private placement warrants issued in connection with ArcLight’s initial public offering were classified as a liability prior to the Closing. As of September 30, 2021, these warrants were continually classified as a liability and measured at fair value, subject to remeasurement at each balance sheet date. Following the Company’s issuance of a redemption notice on September 27, 2021, the private placement warrants and public warrants were identical in terms. See Note 10 for additional information. Accordingly, the fair value of the warrant liability of the private placement warrants as of September 30, 2021 was measured using the trading price of the public warrants. The valuation of the Convertible Notes are based on certain significant inputs not observable in the market, and thus represents a level 3 measure. The key inputs to the valuation model include equity volatility, expected term, and risk-free interest rate. A summary of the changes of the derivative liability and warrant liabilities is as follows (in thousands): Derivative liability Legacy Proterra warrant liability Private placement warrant liability Public warrant liability Fair value as of December 31, 2020 $ 70,870 $ 39,670 $ — $ — Warrant liability acquired as part of the reverse recapitalization — — 57,610 84,640 Change in fair value 111,684 47,346 (37,829) (48,288) Reclassification of liability upon exercise of warrants — (17,696) — — Reclassification of liability upon the reverse recapitalization (182,554) (69,320) — — Fair value as of September 30, 2021 $ — $ — $ 19,781 $ 36,352 The change in fair value of derivative and warrant liabilities is recorded in the statements of operations.

Balance Sheet Components

Balance Sheet Components	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Balance Sheet Components	Balance Sheet Components Cash and cash equivalents consisted of the following (in thousands): September 30, 2021 December 31, 2020 Cash $ 67,924 $ 44,978 Cash equivalents 212,613 65,741 Total cash and cash equivalents $ 280,537 $ 110,719 The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets to the total of such amounts shown on the statements of cash flows. September 30, 2021 December 31, 2020 Cash and cash equivalents $ 280,537 $ 110,719 Restricted cash, current portion 10,890 8,397 Restricted cash, net of current portion 1,675 4,581 Total restricted cash 12,565 12,978 Total cash and cash equivalents, and restricted cash $ 293,102 $ 123,697 Inventories consisted of the following (in thousands): September 30, 2021 December 31, 2020 Raw materials $ 49,880 $ 31,148 Work in progress 27,033 8,042 Finished goods 19,561 47,756 Service parts 6,221 5,384 Total inventories $ 102,695 $ 92,330 The Company recorded a write-down of excess or obsolete inventories to cost of goods sold of $0.6 million and $1.3 million for the three and nine months ended September 30, 2021, and $0.7 million and $2.5 million for the three and nine months ended September 30, 2020, respectively. Property, plant, and equipment, net, consisted of the following (in thousands): September 30, 2021 December 31, 2020 Computer hardware $ 5,099 $ 4,708 Computer software 9,445 8,849 Internally used vehicles and charging systems 19,260 19,136 Leased vehicles and batteries 7,027 7,081 Leasehold improvements 10,459 10,234 Machinery and equipment 24,995 26,026 Office furniture and equipment 1,859 1,854 Tooling 20,782 21,727 Finance lease right-of-use assets 179 179 Construction in progress 10,634 1,830 109,739 101,624 Less: Accumulated depreciation and amortization (56,680) (48,037) Total $ 53,059 $ 53,587 As of September 30, 2021 and December 31, 2020, construction in progress was comprised of various assets that are not available for their intended use as of the balance sheet date. For the nine months ended September 30, 2021, the Company billed approximately $1.4 million of reimbursable equipment costs under the 2019 grant agreement with the California Energy Commission, and offset the costs of machinery and equipment. For the three and nine months ended September 30, 2021, depreciation and amortization expense was $3.9 million and $11.7 million, respectively. For the three and nine months ended September 30, 2020, depreciation and amortization expense was $3.7 million and $11.5 million, respectively. Accrued liabilities consisted of the following (in thousands): September 30, 2021 December 31, 2020 Accrued payroll and related expenses $ 6,827 $ 6,695 Accrued sales and use tax 1,075 975 Warranty reserve 8,117 6,121 Financing obligation 2,346 3,056 Accrued audit and accounting related expenses 683 428 Accrued charger installation costs 1,020 769 Accrued legal expenses 312 510 Other accrued expenses 2,680 1,182 Total $ 23,060 $ 19,736 Other long-term liabilities consisted of the following (in thousands): September 30, 2021 December 31, 2020 Warranty reserve $ 13,395 $ 12,461 Finance lease liabilities, non-current 95 117 Total $ 13,490 $ 12,578 In July 2016, the Company entered into a bus sale and lease transaction for ten Catalyst buses. These buses are leased to other parties for five years by the customer. At the end of the lease term, in the fourth quarter of 2021, the Company has an obligation to repurchase the buses back from the customer. The Company makes a portion of the monthly lease payments directly to the customer and also provide a guarantee to the customer on the remaining lease payments if the lessee fails to pay. The Company received $6.0 million from the customer directly upon delivery in 2016. Under U.S. GAAP, this sales transaction is considered as a borrowing and the lease transaction is considered as an operating lease. The financing obligation was $2.3 million and $3.1 million as of September 30, 2021 and December 31, 2020, respectively. Interest expense on the financing obligation is recognized using the effective interest method. The monthly lease payment is recognized as leasing revenue. The costs of the buses are recorded as leased vehicles in property, plant, and equipment on the balance sheets.

Debt

Debt	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	Debt Debt, net of debt discount and issuance costs, consisted of the following (in thousands): September 30, 2021 December 31, 2020 Senior Credit Facility $ — $ 16,809 PPP loan 10,000 10,000 Convertible Notes 95,896 106,443 Total debt 105,896 133,252 Less debt, current 10,000 — Debt, non-current $ 95,896 $ 133,252 Senior Credit Facility In May 2019, the Company entered into a Loan, Guaranty and Security Agreement for a senior secured asset-based lending facility (the “Senior Credit Facility”) with borrowing capacity up to $75.0 million. The commitment under the Senior Credit Facility is available to the Company on a revolving basis through the earlier of May 2024 or 91 days prior to the stated maturity of any subordinated debt in aggregate amount of $7.5 million or more. The maximum availability under the Senior Credit Facility is based on certain specified percentages of eligible accounts receivable and inventory, subject to certain reserves, to be determined in accordance with the Senior Credit Facility. The commitment under the Senior Credit Facility includes a $15.0 million letter of credit sub-line. Subject to certain conditions, the commitment may be increased by $50.0 million upon approval by the lender, and at the Company’s option, the commitment can be reduced to $25.0 million or terminated upon at least 15 days written notice. The Senior Credit Facility is secured by a security interest in substantially all of the Company’s assets except for intellectual property and other restricted property. Borrowings under the Senior Credit Facility bear interest at per annum rates equal to, at the Company’s option, either (i) the base rate plus an applicable margin for base rate loan, or (ii) the London Interbank Offered Rate (“LIBOR”) plus an applicable margin for LIBOR loan. The base rate is calculated as the greater of (a) the Lender prime rate, (b) the federal funds rate plus 0.5%, and (c) one-month LIBOR plus 1.0%. The applicable margin is calculated based on a pricing grid linked to quarterly average excess availability (as a percentage of borrowing capacity). For base rate loans, the applicable margin ranges from 0.0% to 1.5%, and for LIBOR Loans, it ranges from 1.5% to 3.0%. The Senior Credit Facility contains certain customary non-financial covenants. In addition, the Senior Credit Facility requires the Company to maintain a Fixed Charge Coverage Ratio of at least 1.00:1.00 during such times as a covenant trigger event shall exist. The outstanding balance under the Senior Credit Facility was $17.1 million as of December 31, 2020, with a maturity date in May 2024. The interest rate was 3.09% per annum as of December 31, 2020. In June 2021, the Company made a $17.1 million payment and there was no principal outstanding as of September 30, 2021. The unamortized debt issuance costs of $0.2 million as of September 30, 2021 was recorded in the prepaid expenses and other current assets and other assets on the balance sheets. While there is no debt liability outstanding under this facility, the Company has an aggregate of $10.4 million letters of credit outstanding, using some available capacity, as of September 30, 2021. Small Business Administration Loan In May 2020, the Company received Small Business Administration (“SBA”) loan proceeds of $10.0 million from Town Center Bank pursuant to the Paycheck Protection Program (“the PPP loan”) under the “Coronavirus Aid, Relief and Economic Security (CARES) Act”. The PPP loan was in the form of a note and matures on May 6, 2022. As of September 30, 2021, the interest rate was 1.0% per annum and payable monthly commencing in October 2021. All or a portion of the PPP loan may be forgiven by the SBA upon application with supporting documentation of expenditures in accordance with SBA requirements, which include employees being kept on the payroll for eight weeks after the date of the loan and the proceeds being used for payroll, rent, mortgage interest, or utilities. Convertible Notes In August 2020, the Company entered into a Note Purchase Agreement for Secured Convertible Promissory Notes. The Convertible Notes had an original aggregate principal amount of $200.0 million as of the issuance date with a cash interest of 5.0% per annum payable at each quarter end and a paid-in-kind interest of 4.5% per annum payable by increasing the principal balance at each quarter end. The Convertible Notes will mature in August 2025, and the Company may not make prepayment unless approved by the required holders of the Convertible Notes. In connection with the Closing, the holders had the option to elect to convert the Convertible Notes into shares of common stock. Certain holders of Convertible Notes elected to convert their Convertible Notes into Proterra common stock in connection with the Closing, as described below. At any time after the expiration of the lock-up period following the closing of the Merger, the remaining outstanding Convertible Notes will automatically be converted into Proterra common stock if at any time the volume-weighted average price (VWAP) of the common stock over a period of 20 consecutive trading days exceeds 150% of the conversion price. Based on the determined conversion price, the automatic conversion of the Convertible Notes will be triggered based on a VWAP of $9.86. Each of the Convertible Notes shall rank equally without preference or priority of any kind over one another, but senior in all rights, privileges and preferences to all other shares of the Company’s capital stock and all other securities of the Company that are convertible into or exercisable for the Company’s capital stock directly or indirectly. Prior to the maturity date or prior to the payment or conversion of the entire balance of the Convertible Notes, in the event of a liquidation or sale of the Company, the Company shall pay to the holders of Convertible Notes the greater of (i) 150% of the principal balance of the Convertible Notes or (ii) the consideration that the holders would have received had the holders elected to convert the Convertible Notes into preferred stock immediately prior to such liquidation event. The Convertible Notes do not entitle the holders to any voting rights or other rights as a stockholder of the Company, unless and until the Convertible Notes are actually converted into shares of the Company’s capital stock in accordance with their terms. The Note Purchase Agreement contains certain customary non-financial covenants. In addition, the Note Purchase Agreement requires the Company to maintain liquidity at quarter end of not less than the greater of (i) $75.0 million and (ii) four times of cash burn for the three-month period then ended. The Convertible Notes will mature in August 2025 or will be settled by issuing common stock, and accordingly are classified as a non-current liability on the Company’s balance sheets. In connection with the issuance of the Convertible Notes, the Company issued warrants to the holders of Convertible Notes to purchase 4.6 million shares of Company stock at an exercise price of $0.02 per share. Following the Closing, the stock issuable upon exercise of the warrants is Proterra common stock. The warrants are exercisable for 7 years, and will be automatically exercised in the event of a change of control transaction or the expiration of the warrants. The warrants are freestanding financial instruments and, prior to the Closing, were classified as a liability due to the possibility that they could become exercisable into Legacy Proterra convertible preferred stock. The warrant liability of $29.0 million was initially measured at fair value on its issuance date and recorded as a debt discount, and was amortized during the term of the Convertible Notes to interest expense using the effective-interest method. The warrant liability was remeasured on a recurring basis at each reporting period date, with the change in fair value reported in the statement of operations. Upon any exercise of the warrants to common stock within 5 years from issuance date, the carrying amount of the warrant liability is reclassified to stockholders’ equity. Upon the consummation of the Merger, the stock issuable upon exercise of the warrants is Proterra common stock, with no possibility to convert to Legacy Proterra convertible preferred stock. As a result, the carrying amount of the warrant liability was reclassified to stockholders’ equity. Prior to the Closing, the embedded features of the Convertible Notes were composed of conversion options that had the economic characteristics of a contingent early redemption feature settled in a variable number of shares of Company stock. These conversion options were bifurcated and accounted for separately from the host debt instrument. The derivative liability of $68.5 million was initially measured at fair value on the issuance date of the Convertible Notes and recorded as a debt discount and was amortized during the term of the Convertible Notes to interest expense using the effective-interest method. The derivative liability was remeasured on a recurring basis at each reporting period date, with the change in fair value reported in the statement of operations. Upon the consummation of the Merger, the embedded conversion features associated with the Convertible Notes no longer qualify for derivative accounting since the conversion price became fixed. The carrying amount of the embedded derivative, the fair value as of the Closing Date, was reclassified to stockholders’ equity in accordance with Topic 815, Derivatives and Hedging. Issuance costs of $5.1 million were also recorded as debt discount and will be amortized during the term of the Convertible Notes to interest expense using the effective interest method. On June 14, 2021, certain Convertible Note holders with an original aggregate principal amount of $46.5 million elected to convert their Convertible Notes at the Closing of the Merger. An aggregate of $48.8 million principal and interest was reclassified to additional paid-in capital, and $21.0 million of remaining related debt issuance costs were expensed to interest expense. The amortization expense of debt discount and issuance costs was $3.2 million and $31.5 million for the three and nine months ended September 30, 2021, respectively. The amortization expense of debt discount and issuance costs was $1.9 million and $1.9 million for the three and nine months ended September 30, 2020, respectively. The Convertible Notes, net of debt discount and issuance costs, consisted of the following (in thousands): September 30, 2021 December 31, 2020 Principal $ 153,500 $ 200,000 PIK interest 7,994 3,501 Total principal 161,494 203,501 Less debt discount and issuance costs (65,598) (97,058) Total Convertible Notes $ 95,896 $ 106,443 As of September 30, 2021, the contractual future principal repayments of the total debt were as follows (in thousands): 2022 $ 10,000 2025 (1) 161,494 Total debt $ 171,494 __________________

Leases

Leases	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Leases	Leases As a Lessor The net investment in leases consisted of the following (in thousands): September 30, 2021 December 31, 2020 Net investment in leases, current $ 411 $ 398 Net investment in leases, non-current 4,838 3,101 Total net investment in leases $ 5,249 $ 3,499 Interest income from accretion of net investment in leases is not material in the three and nine months ended September 30, 2021 or 2020. In the nine months ended September 30, 2021, the Company assigned one operating lease and one sales-type lease. The Company received a total of $1.2 million in cash, and recorded $0.4 million in product revenue for the assigned operating lease in the statement of operations. Future minimum payments receivable from operating and sales-type leases as of September 30, 2021 for each of the next five years are as follows: Operating leases Sales-type leases Remainder of 2021 $ — $ 99 2022 — 395 2023 — 469 2024 — 485 2025 — 758 Thereafter — 3,592 Total minimum lease payments $ — $ 5,798 As a Lessee The Company leases its office and manufacturing facilities in Burlingame and City of Industry, California, Greenville, South Carolina, and Rochester Hills, Michigan under operating lease agreements with various expiration dates through 2026. In June 2018, the Company entered into an agreement to sublease its office facilities in Rochester Hills, Michigan from July 2018 to October 2023. The sublease income is recorded in the other expense (income), net on the statement of operations. Maturities of operating lease liabilities as of September 30, 2021 were as follows (in thousands): Remainder of 2021 $ 1,036 2022 3,650 2023 2,808 2024 1,685 2025 1,039 Thereafter 443 Total undiscounted lease payment 10,661 Less: imputed interest (775) Total operating lease liabilities $ 9,886 Operating lease expense was $1.0 million for the three months ended September 30, 2021 and 2020, and $3.0 million for the nine months ended September 30, 2021 and 2020, respectively. Short-term and variable lease expenses for the three and nine months ended September 30, 2021 and 2020 were not material. Supplemental cash flow information related to leases were as follows (in thousands): Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ (3,050) $ (1,901) In the nine months ended September 30, 2021, $1.5 million operating lease right-of-use assets were obtained in exchange for lease liabilities, and the cash flow from financing leases was not material. In the nine months ended September 30, 2020, the cash flow from financing leases and right-of-use assets obtained in exchange for lease obligations were not material. Operating lease right-of-use assets and liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 Operating leases Operating lease right-of-use assets $ 9,234 $ 10,310 Operating lease liabilities, current 3,583 3,153 Operating lease liabilities, non-current 6,303 7,891 Total operating lease liabilities $ 9,886 $ 11,044 The weighted average remaining lease term and discount rate of operating leases are 3.3 years and 4.6%, respectively, as of September 30, 2021. As of September 30, 2021, the Company had no significant additional operating leases and finance leases that have not yet commenced.
Leases	Leases As a Lessor The net investment in leases consisted of the following (in thousands): September 30, 2021 December 31, 2020 Net investment in leases, current $ 411 $ 398 Net investment in leases, non-current 4,838 3,101 Total net investment in leases $ 5,249 $ 3,499 Interest income from accretion of net investment in leases is not material in the three and nine months ended September 30, 2021 or 2020. In the nine months ended September 30, 2021, the Company assigned one operating lease and one sales-type lease. The Company received a total of $1.2 million in cash, and recorded $0.4 million in product revenue for the assigned operating lease in the statement of operations. Future minimum payments receivable from operating and sales-type leases as of September 30, 2021 for each of the next five years are as follows: Operating leases Sales-type leases Remainder of 2021 $ — $ 99 2022 — 395 2023 — 469 2024 — 485 2025 — 758 Thereafter — 3,592 Total minimum lease payments $ — $ 5,798 As a Lessee The Company leases its office and manufacturing facilities in Burlingame and City of Industry, California, Greenville, South Carolina, and Rochester Hills, Michigan under operating lease agreements with various expiration dates through 2026. In June 2018, the Company entered into an agreement to sublease its office facilities in Rochester Hills, Michigan from July 2018 to October 2023. The sublease income is recorded in the other expense (income), net on the statement of operations. Maturities of operating lease liabilities as of September 30, 2021 were as follows (in thousands): Remainder of 2021 $ 1,036 2022 3,650 2023 2,808 2024 1,685 2025 1,039 Thereafter 443 Total undiscounted lease payment 10,661 Less: imputed interest (775) Total operating lease liabilities $ 9,886 Operating lease expense was $1.0 million for the three months ended September 30, 2021 and 2020, and $3.0 million for the nine months ended September 30, 2021 and 2020, respectively. Short-term and variable lease expenses for the three and nine months ended September 30, 2021 and 2020 were not material. Supplemental cash flow information related to leases were as follows (in thousands): Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ (3,050) $ (1,901) In the nine months ended September 30, 2021, $1.5 million operating lease right-of-use assets were obtained in exchange for lease liabilities, and the cash flow from financing leases was not material. In the nine months ended September 30, 2020, the cash flow from financing leases and right-of-use assets obtained in exchange for lease obligations were not material. Operating lease right-of-use assets and liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 Operating leases Operating lease right-of-use assets $ 9,234 $ 10,310 Operating lease liabilities, current 3,583 3,153 Operating lease liabilities, non-current 6,303 7,891 Total operating lease liabilities $ 9,886 $ 11,044 The weighted average remaining lease term and discount rate of operating leases are 3.3 years and 4.6%, respectively, as of September 30, 2021. As of September 30, 2021, the Company had no significant additional operating leases and finance leases that have not yet commenced.
Leases	Leases As a Lessor The net investment in leases consisted of the following (in thousands): September 30, 2021 December 31, 2020 Net investment in leases, current $ 411 $ 398 Net investment in leases, non-current 4,838 3,101 Total net investment in leases $ 5,249 $ 3,499 Interest income from accretion of net investment in leases is not material in the three and nine months ended September 30, 2021 or 2020. In the nine months ended September 30, 2021, the Company assigned one operating lease and one sales-type lease. The Company received a total of $1.2 million in cash, and recorded $0.4 million in product revenue for the assigned operating lease in the statement of operations. Future minimum payments receivable from operating and sales-type leases as of September 30, 2021 for each of the next five years are as follows: Operating leases Sales-type leases Remainder of 2021 $ — $ 99 2022 — 395 2023 — 469 2024 — 485 2025 — 758 Thereafter — 3,592 Total minimum lease payments $ — $ 5,798 As a Lessee The Company leases its office and manufacturing facilities in Burlingame and City of Industry, California, Greenville, South Carolina, and Rochester Hills, Michigan under operating lease agreements with various expiration dates through 2026. In June 2018, the Company entered into an agreement to sublease its office facilities in Rochester Hills, Michigan from July 2018 to October 2023. The sublease income is recorded in the other expense (income), net on the statement of operations. Maturities of operating lease liabilities as of September 30, 2021 were as follows (in thousands): Remainder of 2021 $ 1,036 2022 3,650 2023 2,808 2024 1,685 2025 1,039 Thereafter 443 Total undiscounted lease payment 10,661 Less: imputed interest (775) Total operating lease liabilities $ 9,886 Operating lease expense was $1.0 million for the three months ended September 30, 2021 and 2020, and $3.0 million for the nine months ended September 30, 2021 and 2020, respectively. Short-term and variable lease expenses for the three and nine months ended September 30, 2021 and 2020 were not material. Supplemental cash flow information related to leases were as follows (in thousands): Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ (3,050) $ (1,901) In the nine months ended September 30, 2021, $1.5 million operating lease right-of-use assets were obtained in exchange for lease liabilities, and the cash flow from financing leases was not material. In the nine months ended September 30, 2020, the cash flow from financing leases and right-of-use assets obtained in exchange for lease obligations were not material. Operating lease right-of-use assets and liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 Operating leases Operating lease right-of-use assets $ 9,234 $ 10,310 Operating lease liabilities, current 3,583 3,153 Operating lease liabilities, non-current 6,303 7,891 Total operating lease liabilities $ 9,886 $ 11,044 The weighted average remaining lease term and discount rate of operating leases are 3.3 years and 4.6%, respectively, as of September 30, 2021. As of September 30, 2021, the Company had no significant additional operating leases and finance leases that have not yet commenced.

Commitments and Contingencies

Commitments and Contingencies	9 Months Ended
	Sep. 30, 2021
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Commitments and Contingencies Purchase Commitments As of September 30, 2021, the Company had outstanding inventory and other purchase commitments of $623.7 million. Letters of Credit As of September 30, 2021, the Company had letters of credit outstanding totaling $10.5 million, which will expire over various dates in 2021 and 2022. Guarantees The Company provides guarantees of lease payments for vehicles under the financing transaction discussed in Note 5, in the event the lessee does not make payments to the financing company. The Company regularly reviews its performance risk under the arrangement, and in the event that it becomes probable that it will be required to perform under a guarantee, the fair value of probable payment will be recorded. No guarantee liability was recorded as of September 30, 2021 and December 31, 2020. Legal Proceedings The Company accrues contingent liabilities when it is probable that future expenditures will be made and such expenditures can be reasonably estimated. From time to time in the normal course of business, various claims and litigation have been asserted or commenced. Due to uncertainties inherent in litigation and other claims, the Company can give no assurance that it will prevail in any such matters, which could subject the Company to significant liability or damages. Any claims or litigation could have an adverse effect on the Company’s business, financial position, operating results, or cash flows in or following the period that claims or litigation are resolved.

Stockholders' Equity

Stockholders' Equity	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Stockholders' Equity	Stockholders’ Equity On June 14, 2021, the Merger was consummated and, following the Closing, the Company is authorized to issue 510,000,000 shares of capital stock, with a par value of $0.0001 per share. The authorized shares consisted of 500,000,000 shares of common stock and 10,000,000 shares of preferred stock. As of September 30, 2021, 212,827,249 shares of common stock were issued and outstanding, and no shares of preferred stock were issued and outstanding. The holders of each share of common stock are entitled to one vote per share. The Company has retroactively adjusted the shares of Legacy Proterra stock issued and outstanding prior to June 14, 2021 to give effect to the Exchange Ratio of 0.8925 established in the Merger Agreement to determine the number of shares of Proterra common stock into which they were converted. Immediately prior to the Merger, Legacy Proterra was authorized to issue 271,920,636 shares of stock, with a par value of $0.0001 per share, with 156,276,750 shares designated as common stock and 115,643,886 shares of convertible preferred stock. All of the outstanding Legacy Proterra convertible preferred stock was converted to Legacy Proterra common stock immediately prior to the Merger. See Note 3, Reverse Recapitalization. In August 2021, in order to satisfy the withholding tax liability of certain employees who received the First Earnout Shares, the Company repurchased 64,304 shares of common stock from these employees for $634,037. The repurchased shares were retired immediately. The Company had reserved shares of common stock for issuance as follows (in thousands): September 30, 2021 2010 Equity Incentive Plan 21,654 2021 Equity Incentive Plan 10,591 2021 Employee Stock Purchase Plan 1,630 Warrants 24,862 Earnout Stock 18,009 Total 76,746

Warrants

Warrants	9 Months Ended
	Sep. 30, 2021
Other Liabilities Disclosure [Abstract]
Warrants	Warrants Public Warrants Public warrants were only exercisable for a whole number of shares of common stock at a price of $11.50 per share, subject to adjustment, at any time commencing on September 25, 2021, provided in each case that the Company had an effective registration statement under the Securities Act covering the common stock issuable upon exercise of the warrants and a current prospectus relating to them was available (or the Company permitted holders to exercise their warrants on a cashless basis under the circumstances specified in the Amended and Restated Warrant Agreement) and such shares were registered, qualified or exempt from registration under the securities, or blue sky, laws of the state of residence of the holder. The warrants were to expire June 14, 2026 or earlier upon redemption or liquidation. The Company had agreed that it would use its commercially reasonable efforts to maintain the effectiveness of the registration statement and a current prospectus relating to those shares of common stock until the warrants expired or were redeemed, as specified in the Amended and Restated Warrant Agreement. During any period when the Company failed to maintain an effective registration statement covering the issuance of the common stock issuable up exercise of the warrants, holders of the warrants had the right to exercise warrants on a “cashless basis” in accordance with Section 3(a)(9) of the Securities Act or another exemption. Once the warrants became exercisable, the Company was able to redeem the outstanding warrants (except as described herein with respect to the private placement warrants): Redemption of warrants when the price per share of common stock equals or exceeds $18.00. Once the warrants become exercisable, the Company may redeem the outstanding warrants: • in whole and not in part; • at a price of $0.01 per warrant; • upon a minimum of 30 days’ prior written notice of redemption to each warrant holder; and • if, and only if, the closing price of the common stock equaled or exceeded $18.00 per share (as adjusted for share splits, share capitalizations, reorganizations, recapitalizations and the like) for any 20 trading days within a 30-trading day period ending three trading days before the Company sent the notice of redemption to the warrant holders. The Company was not able to redeem the warrants as described above unless a registration statement under the Securities Act covering the issuance of the common stock issuable upon exercise of the warrants was then effective and a current prospectus relating to those common stock was available throughout the 30-day redemption period. If and when the warrants became redeemable by the Company, the Company was able to exercise its redemption right even if the Company was unable to register or qualify the underlying securities for sale under all applicable state securities laws. Redemption of warrants when the price per share of common stock equals or exceeds $10.00. Once the warrants became exercisable, the Company was able to redeem the outstanding warrants: • in whole and not in part; • at $0.10 per warrant upon a minimum of 30 days’ prior written notice of redemption provided that holders were able to exercise their warrants on a cashless basis prior to redemption and receive that number of shares determined by reference to the make-whole exercise table specified in the Amended and Restated Warrant Agreement, based on the redemption date and the “fair market value” of common stock (as provided in such table) except as otherwise provided for in the Amended and Restated Warrant Agreement; and • if, and only if, the closing price of the shares of common stock equaled or exceeded $10.00 per public share (as adjusted for share subdivisions, share dividends, reorganizations, reclassifications, recapitalizations and the like) for any 20 trading days within the 30-trading day period ending three trading days before the Company sent the notice of redemption to the warrant holders. In addition, if the closing price of the common stock for any 20 trading days within a 30-trading day period ending on the third trading day prior to the date on which the Company sent the notice of redemption to the warrant holders was less than $18.00 per share (as adjusted for share subdivisions, share dividends, reorganizations, reclassifications, recapitalizations and the like), the private placement warrants could also be, and were, concurrently called for redemption on the same terms as the outstanding public warrants, as described above. Beginning on the date the notice of redemption was given until the warrants were redeemed or exercised, holders were able to elect to exercise their warrants on a cashless basis. The public warrants were classified as liabilities as they did not meet the requirements for equity classification under Topic 815, Derivatives and Hedging. Immediately prior to the Closing, the warrant liability was $84.6 million. Such warrants were measured at fair value, subject to remeasurement at each balance sheet date. Private Placement Warrants Except as described below, the private placement warrants had terms and provisions that were identical to those of the public warrants. The private placement warrants (including the shares of common stock issuable upon exercise of the private placement warrants) were not transferable, assignable or salable until July 14, 2021, except pursuant to limited exceptions to the Company’s officers and directors and other persons or entities affiliated with the Sponsor, and they were not redeemable by the Company, except as described above when the price per share of common stock equaled or exceeded $10.00, so long as they were held by the Sponsor or its permitted transferees (except as otherwise set forth herein). The Sponsor, or its permitted transferees, had the option to exercise the private placement warrants on a cashless basis. If the private placement warrants were held by holders other than the Sponsor or its permitted transferees, the private placement warrants were redeemable by the Company in all redemption scenarios and exercisable by the holders on the same basis as the public warrants. Any amendment to the terms of the private placement warrants or any provision of the Amended and Restated Warrant Agreement with respect to the private placement warrants required a vote of holders of at least 65% of the number of the then outstanding private placement warrants. The private placement warrants were classified as liabilities as they did not meet the requirements for equity classification under Topic 815, Derivatives and Hedging. Immediately prior to the Closing, the warrant liability was $57.6 million. Such warrants were measured at fair value, subject to remeasurement at each balance sheet date. On September 27, 2021, the Company announced that it would be redeeming all of its outstanding public warrants and private placement warrants (collectively, the “Warrants”) based on the terms in the Amended and Restated Warrant Agreement dated June 14, 2021. On October 29, 2021 (the “Redemption Date”), any Warrants that remained unexercised became void and no longer exercisable, and the holders of those Warrants were entitled to receive only the redemption price of $0.10 per Warrant. In connection with the redemption, holders of Warrants had the option to either exercise the Warrants in cash or on a “cashless” basis to receive 0.255 shares of common stock per warrant. See Note 14, Subsequent events. Legacy Proterra Warrants As of September 30, 2021, the Company had 3,422,794 common stock warrants outstanding exchanged for Legacy Proterra warrants, including 3,421,902 warrants issued to the holders of Convertible Notes as described in Note 6. Activity of warrants in the nine months period ended September 30, 2021 is as follows: Public warrants Private placement warrants Other warrants Total warrants Outstanding as of December 31, 2020 — — 5,104,030 5,104,030 Issued as part of the Merger 13,874,994 7,550,000 — 21,424,994 Exercised 1 — — (1,681,236) (1,681,236) Outstanding as of September 30, 2021 13,874,994 7,550,000 3,422,794 24,847,788 __________________ 1. Certain warrant holders elected to net exercise their warrants, and as a result, an aggregate of 1,564,958 shares of common stock were issued.

Equity Plans and Stock-based Co

Equity Plans and Stock-based Compensation	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Equity Plans and Stock-based Compensation	Equity Plans and Stock-based Compensation 2010 Equity Incentive Plan Legacy Proterra’s 2010 Equity Incentive Plan (the “2010 Plan”) was terminated upon the effective date of Proterra’s 2021 Equity Incentive Plan (the “2021 Plan”), and accordingly, no shares will be available for grant under the 2010 Plan. Upon Closing, the outstanding awards under the 2010 Plan were converted into options exercisable to purchase an aggregate of 22,532,619 shares of common stock. Following the Closing, the exchanged options continue to be subject to the terms of the 2010 Plan and applicable award agreements. As of September 30, 2021, options to purchase 21,653,662 shares of common stock remained outstanding under the 2010 Plan. 2021 Equity Incentive Plan The 2021 Plan was adopted by the ArcLight Board prior to the Closing, approved by ArcLight’s shareholders on June 11, 2021, and became effective upon the Closing Date. The Equity Incentive Plan allows the Company to grant awards of stock options, restricted stock awards, stock appreciation rights (“SARs”), restricted stock units (“RSUs”), performance awards, and stock bonus awards to officers, employees, directors and consultants. The Company initially reserved 10,000,000 shares of common stock, plus 387,513 reserved shares not issued under the 2010 Plan on the effective date of the 2021 Plan. The number of shares reserved for issuance under the 2021 Plan will increase automatically on January 1 of each of 2022 through 2031 by the number of shares equal to the lesser of 4% of the total number of outstanding shares of all classes of common stock as of the immediately preceding December 31, or a number as may be determined by the Board. The exercise price of stock options granted must be at least equal to the fair market value of common stock on the date of grant. Incentive stock options granted to an individual who holds, directly or by attribution, more than ten percent of the total combined voting power of all classes of capital stock must have an exercise price of at least 110% of the fair market value of common stock on the date of grant. Subject to certain adjustments, no more than 30,000,000 shares may be issued pursuant to the exercise of incentive stock options granted under the 2021 Plan. The maximum term of options granted is ten years from the date of grant, except that the maximum permitted term of incentive stock options granted to an individual who holds, directly or by attribution, more than ten percent of the total combined voting power of all classes of capital stock is five years from the date of grant. Stock option and RSU awards generally vest annually over a four-year period. Certain awards have shorter vesting periods. 2021 Employee Stock Purchase Plan Proterra’s 2021 Employee Stock Purchase Plan (the “ESPP”), including the authorization of the initial share reserve thereunder, was adopted by the ArcLight Board prior to the Closing, approved by ArcLight’s shareholders on June 11, 2021, and became effective upon the Closing Date. An aggregate of 1,630,000 shares of common stock were reserved and available for sale under the ESPP. The aggregate number of shares reserved for sale under the ESPP will increase automatically on January 1 of each of 2022 through 2031 by a number of shares equal to the lesser of 1% of the total number of outstanding shares of common stock as of the immediately preceding December 31 or a number of shares as may be determined by the Board or the compensation committee. The aggregate number of shares issued over the term of the ESPP, subject to certain adjustments, may not exceed 16,300,000 shares. A summary of the Company’s stock option activity and related information was as follows: Options Outstanding Number of Stock Options Outstanding Weighted- Average Exercise Price Weighted-Average Remaining Contractual Life Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2020 (1) 20,178,784 3.81 7.4 $ 65,056 Granted 674,643 9.86 Exercised (1,676,533) 3.24 Cancelled/forfeited/expired (513,463) 5.09 Balance as of September 30, 2021 (2) 18,663,431 4.04 6.9 $ 113,302 Exercisable as of September 30, 2021 (3) 12,592,271 3.35 6.0 $ 85,124 __________________ (1) Excluding Equity Awards of 2,677,500 shares and Milestone Options of 669,375 shares outstanding, of which 502,031 shares vested and exercisable as of December 31, 2020. Refer to section below for further details. (2) Excluding Equity Awards of 2,677,500 shares and Milestone Options of 669,375 shares outstanding as of September 30, 2021. (3) Excluding 1,004,064 shares exercisable under the Equity Awards with weighted average exercise price of $19.61 per share as of September 30, 2021. In March 2020, in conjunction with Mr. Allen’s appointment as the President and Chief Executive Officer, the board of directors approved a grant to Mr. Allen of stock option awards with respect to 4,685,624 shares, comprised of (1) 1,338,749 shares of a time-based award with an exercise price of $5.33 per share vesting quarterly over 4 years, (2) 2,677,500 shares of a time-based award consisting of 4 tranches with an exercise price of $11.21, $16.81, $22.41 and $28.02 per share, respectively, and vesting quarterly over 4 years (“Equity Awards”), and (3) 669,375 shares of milestone-based award with an exercise price of $5.33 per share vesting entirely and becoming exercisable on the first trading day following the expiration of the lockup period of the Company’s initial public offering or the consummation of a change in control of the Company or upon the consummation of a merger involving a Special Purpose Acquisition Company (“Milestone Options”). The stock-based compensation expense for Milestone Options was recognized at the time the performance milestone became probable of achievement, which was at the time of Closing. Upon Closing, the 669,375 shares underlying the Milestone Options fully vested, and $2.1 million stock-based compensation expense was recognized in June 2021. Aggregate intrinsic value represents the difference between the estimated fair value of the underlying common stock and the exercise price of outstanding, in-the-money stock options. The total intrinsic value of stock options exercised was $10.3 million for the nine months ended September 30, 2021. The total estimated grant date fair value of stock options vested was $10.2 million for the nine months ended September 30, 2021. As of September 30, 2021, the total unrecognized stock-based compensation expense related to outstanding stock options was $27.3 million, which is expected to be recognized over a weighted-average period of 2.5 years. Determining Fair Value of Stock Options The fair value of stock options granted is estimated on the date of grant using the following assumptions: Nine Months Ended September 30, 2021 2020 Expected term (in years) 6.2 6.0 Risk-free interest rate 1.0 % 0.5 % Expected volatility 53.9 % 73.1 % Expected dividend rate — — Restricted Stock Units A summary of the Company's RSU activity and related information is as follows: Number of RSUs Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Balance as of December 31, 2020 — $ — $ — Granted 857,199 11.33 Vested — — Forfeited (9,441) 11.33 Balance as of September 30, 2021 847,758 $ 11.33 $ 8,571 During the three and nine months ended September 30, 2021, the Company granted RSUs to certain employees. All RSUs are subject to a time-based vesting condition for approximately four years. As of September 30, 2021, the total unrecognized stock-based compensation expense related to outstanding RSUs was $9.3 million, which is expected to be recognized over a weighted-average period of 3.6 years. Stock-based Compensation Expense Stock-based compensation expense included in operating results was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Cost of goods sold $ 319 $ 235 $ 865 $ 688 Research and development 567 461 1,625 1,183 Selling, general and administrative 2,292 1,984 8,775 5,680 Total stock-based compensation expense $ 3,178 $ 2,680 $ 11,265 $ 7,551

Net Income (Loss) Per Share

Net Income (Loss) Per Share	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Net Income (Loss) Per Share	Net Income (Loss) Per Share Basic net loss per share is computed by dividing the net loss by the weighted-average number of shares of common stock outstanding during the period, less the weighted-average unvested common stock subject to repurchase or forfeiture as they are not deemed to be issued for accounting purposes. Diluted net loss per share is computed by giving effect to all potential shares of common stock, including stock options and warrants, to the extent they are dilutive. The computation of the Company’s basic and diluted net income (loss) per share of common stock attributable to common stockholders was as follows (in thousands, except for per share data): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Numerator: Net income (loss) $ 36,321 $ (46,860) $ (204,868) $ (94,384) Effect of dilutive securities: Gain on valuation of warrant liabilities (73,197) — — — Interest expense to be recognized upon conversion of Convertible Notes (1) (61,774) — — — Numerator for diluted EPS - Net loss after the effect of dilutive securities $ (98,650) $ (46,860) $ (204,868) $ (94,384) Denominator: Basic weighted average shares (2) 212,071 4,406 89,233 4,139 Dilutive impact of public and private placement warrants 594 — — — Convertible Notes (1) 24,300 — — — Diluted weighted average shares 236,965 4,406 89,233 4,139 Net income (loss) per share of common stock: Basic $ 0.17 $ (10.64) $ (2.30) $ (22.80) Diluted $ (0.42) $ (10.64) $ (2.30) $ (22.80) _____________ (1) Adjustment is under the “if-converted” method, and includes write-off of $68.8 million unamortized debt discount of the Convertible Notes as of June 30, 2021, offset by the $7.0 million interest expense recorded in net income of the third quarter of 2021. (2) Includes the remaining outstanding warrants issued in connection with the Convertible Notes with an exercise price of $0.02 per share as of the Closing Date. The exercise of these warrants is virtually assured based on common stock trading price since the Closing Date. Therefore, the outstanding shares are included in the denominator of both the basic and diluted EPS calculation. In addition, prior to the Closing Date, such warrants were liability classified, and accordingly excluded from EPS calculation. As a result of the Merger, the Company has retroactively adjusted the weighted-average number of shares of common stock outstanding prior to the Closing Date by multiplying them by the Exchange Ratio of 0.8925 used to determine the number of shares of common stock into which they converted. The common stock issued as a result of the convertible preferred stock conversion on the Closing Date was included in the basic net loss per share calculation on a prospective basis. Prior to the Closing Date, the Company applied the two-class method to calculate its basic and diluted net loss per share of common stock, as the convertible preferred stock were participating securities. The two-class method is an earnings allocation formula that treats a participating security as having rights to earnings that otherwise would have been available to common stockholders. However, the two-class method did not impact the net loss per share of common stock as the Company was in a loss position for each of the periods presented and holders of convertible preferred stock did not participate in losses. Post the Closing Date, the Company applies the treasury stock method when calculating the diluted net income (loss) per share of common stock and “if-converted” method for Convertible Notes when applicable. Since the Company was in a loss position after the effect of dilutive securities, no adjustment is required to the weighted-average shares used in computing the diluted net income (loss) per share as the inclusion of all potential common stock shares outstanding would have been anti-dilutive. The potentially dilutive securities were as follows (in thousands): September 30, 2021 Stock options and RSUs 22,858 Other warrants to purchase common stock 1 22,859

401(k) Plan

401(k) Plan	9 Months Ended
	Sep. 30, 2021
Retirement Benefits [Abstract]
401(k) Plan	401(k) Plan The Company sponsors a 401(k) defined contribution plan covering all eligible employees and provides a matching contribution for the first 4% of their salaries. The matching contribution costs incurred were $0.6 million and $0.5 million in the three months ended September 30, 2021 and 2020, and $1.8 million and $1.4 million in the nine months ended September 30, 2021 and 2020, respectively.

Subsequent Events

Subsequent Events	9 Months Ended
	Sep. 30, 2021
Subsequent Events [Abstract]
Subsequent Events	Subsequent Events On September 27, 2021, the Company announced that it would be redeeming all of its outstanding public warrants and private placement warrants. In connection with the redemption, in October 2021, 10,599 public warrants were exercised for cash resulting in the issuance of 10,599 shares of common stock for an aggregate exercise price of $121,889, 13,436,250 public warrants and 7,550,000 private placement warrants were exercised on “cashless basis” resulting in the issuance of 5,351,231 shares of common stock, and 428,145 public warrants were redeemed for cash for an aggregate redemption price of $42,815. These warrants were classified as liability prior to exercise and measured at fair value with the change in fair value reported in the statement of operations. Upon any exercise of such warrants to common stock, the carrying amount of the warrant liability was reclassified to stockholders’ equity. In October 2021, $2.7 million gain in change in fair value was recorded in the statement of operations, and $53.4 million of the carrying amount of the warrant liability was reclassified to stockholder’s equity.

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 unaudited condensed consolidated financial statements and accompanying notes have been prepared in accordance with U.S. generally accepted accounting principles (“U.S. GAAP”) and the rules and regulations of the U.S. Securities and Exchange Commission (the “SEC”). The Company’s condensed consolidated financial statements include the accounts of the Company and its wholly-owned subsidiaries. All intercompany transactions and balances have been eliminated upon consolidation. Certain information and footnote disclosures normally included in consolidated financial statements prepared in accordance with U.S. GAAP have been condensed or omitted pursuant to such rules and regulations. Accordingly, these condensed consolidated financial statements should be read in conjunction with the audited financial statements for the year ended December 31, 2020 and the related notes incorporated by referenced in the Company’s Current Report on Form 8-K, filed with SEC on June 17, 2021, which provides a more complete discussion of the Company’s accounting policies and certain other information. The information as of December 31, 2020 and 2019 was derived from the Company’s audited financial statements. The condensed consolidated financial statements were prepared on the same basis as the audited financial statements and, in the opinion of management, reflect all adjustments, which include only normal recurring adjustments necessary for a fair presentation of the Company’s financial position as of September 30, 2021 and the results of operations and cash flows for the three and nine months ended September 30, 2021 and 2020. The results of operations for the three and nine months ended September 30, 2021 are not necessarily indicative of the results that may be expected for the year ending December 31, 2021. There have been no changes to the Company’s significant accounting policies described in the annual financial statements for the year ended December 31, 2020, except for the new accounting policies adopted during the three months ended June 30, 2021 related to public warrants and private placement warrants described below, that have had a material impact on the Company’s condensed consolidated financial statements and related notes. The Company has not experienced any significant impact to estimates or assumptions as a result of the COVID-19 pandemic. However, there have been some impacts, specifically as it relates to parts, logistics and overall transit order timing. The Company will continue to monitor impacts of the pandemic on an ongoing basis. While the COVID-19 pandemic has not had a material adverse impact on the Company’s financial condition and results of operations to date, the future impact of the COVID-19 pandemic on the Company’s operational and financial performance will depend on certain developments, including the duration of the pandemic and spread of COVID-19 (including the variant strains of the virus), impact on the Company’s customers and effect on the Company’s suppliers, all of which are uncertain and cannot be predicted.
Segments	SegmentsThe Company operates in the United States and has sales to the European Union, Canada, Australia and Japan. The revenue generated outside of the United States in 2020 was mainly from sales to customers in Canada. The Company’s chief operating decision maker is its Chief Executive Officer (CEO), who reviews financial information presented at the entity level. Accordingly, the Company has determined that it has a single reportable segment.
Foreign Currency Transactions	Foreign Currency Transactions Net gains or losses resulting from foreign exchange transactions were not material for all periods presented.
Accounts Receivable and Allowance for Credit Losses	Accounts Receivable and Allowance for Credit Losses Accounts receivable are recorded at the invoiced amount and do not bear interest. The Company determines the allowance for credit losses based on historical write-off experience, an analysis of the aging of outstanding receivables, customer payment patterns and expectations of changes in macroeconomic conditions that may affect the collectability of outstanding receivables. The allowance for credit losses was not material as of September 30, 2021 and December 31, 2020.
Short-Term Investments	Short-Term Investments The Company’s primary objectives for investment activities are to preserve principal, provide liquidity, and maximize income without significantly increasing risk. The Company’s short-term investments were primarily comprised of U.S. Treasury and corporate debt securities, and classified as available-for-sale at the time of purchase because it is intended that these investments are available for current operations. Investments are reported at fair value and are subject to periodic impairment review. Unrealized gains and losses related to changes in the fair value of these securities will be recognized in accumulated other comprehensive loss. The ultimate
Restricted Cash	Restricted Cash The Company maintains certain cash amounts restricted as to withdrawal or use. The restricted cash is primarily collateral for performance bonds issued to certain customers. The collateral is provided in the form of a cash deposit to either support the bond directly or to collateralize a letter of credit that supports the performance bonds.
Credit Risk and Concentration	Credit Risk and Concentration The Company’s financial instruments that are potentially subject to concentrations of credit risk consist primarily of cash, cash equivalents, restricted cash, short-term investments, and accounts receivable. Cash and cash equivalents and short-term investments are maintained primarily at a financial institution as of September 30, 2021, and deposits exceed federally insured limits. Risks associated with cash and cash equivalents, and short-term investments are mitigated by banking with creditworthy financial institutions. The Company has not experienced any losses on its deposits of cash and cash equivalents or its short-term investments. Cash equivalents and short-term investments consist of short-term money market funds, corporate debt securities, and debt securities issued by the U.S. Treasury, which are deposited with reputable financial institutions. The Company’s cash management and investment policy limits investment instruments to investment-grade securities with the objective to preserve capital and to maintain liquidity until the funds can be used in business operations. Accounts receivable are typically unsecured and are generally derived from revenue earned from transit agencies, universities and airports in North America and global commercial vehicle manufacturers in North America, the European Union, Australia and Japan. The Company periodically evaluates the collectability of its accounts receivable and provides an allowance for potential credit losses as necessary. Given the large order value for customers and the relatively low number of customers, revenue and accounts receivable have typically been concentrated with a limited number of customers. Revenue Accounts Receivable Three Months Ended September 30, Nine Months Ended September 30, September 30, December 31, 2021 2020 2021 2020 2021 2020 Number of customers accounted for 10% or more* 2 4 — 4 2 2 __________________ * One customer accounted for 33% of accounts receivable, net as of December 31, 2020. No other individual customer accounted for more than 20% of the Company's revenue for the three and nine months ended September 30, 2021 and 2020, or accounts receivable as of September 30, 2021 and December 31, 2020. Single source suppliers provide the Company with a number of components that are required for manufacturing of its current products. In other instances, although there may be multiple suppliers available, many of the components are purchased from a single source. If these single source suppliers fail to meet the Company’s requirements on a timely basis at competitive prices, the Company could suffer manufacturing delays, a possible loss of revenue, or incur higher cost of sales, any of which could adversely impact the Company’s operating results.
Fair Value of Financial Instruments	Fair Value of Financial Instruments The carrying value of the Company’s financial instruments, including cash and cash equivalents, accounts receivable, short-term investments, accounts payable, and accrued and other current liabilities, approximates fair value due to the short period of time to maturity, receipt, or payment. The carrying amount of the Company’s debt, except for Convertible Notes (as defined below), approximates its fair value as the stated interest rates approximate market rates currently available to the Company. In August 2020, the Company issued Secured Convertible Promissory Notes (the “Convertible Notes”) that, prior to the Closing, contained embedded features subject to derivative accounting. These embedded features were composed of conversion options that had the economic characteristics of a contingent early redemption feature settled in a variable number of shares of the Company’s stock. These conversion options were bifurcated and accounted for as a derivative liability separately from the host debt instrument. Embedded derivatives were recognized as a derivative liability on the balance sheet. The derivative liability was measured at fair value and subject to remeasurement at each balance sheet date. Upon the consummation of the Merger, the embedded conversion features associated with the Convertible Notes no longer qualify for derivative accounting after the conversion price became fixed. The carrying amount of the embedded derivative, the fair value as of the date of the Closing, was reclassified to stockholders’ equity in accordance with Topic 815, Derivatives and Hedging. The warrants issued in connection with the Convertible Notes were, prior to the Closing, classified as a liability (“legacy Proterra warrant liability”) because they could become exercisable into common stock upon a Qualified Initial Public Offering (“QIPO”) or into convertible preferred stock after 5 years from issuance date in the event that there was no QIPO during such period. Such warrants were measured at fair value, subject to remeasurement at each balance sheet date. Upon exercise of the warrants to common stock within 5 years from issuance date, the carrying amount of the warrant liability would be reclassified to stockholders’ equity. Upon the consummation of the Merger, the stock issuable upon exercise of the warrants is common stock, with no possibility to convert to Legacy Proterra convertible preferred stock. As a result, the carrying amount of the warrant liability was reclassified to stockholders’ equity. In connection with ArcLight’s initial public offering in September 2020, 21,425,000 warrants to purchase ArcLight ordinary shares were issued, including 13,875,000 public warrants and 7,550,000 private placement warrants. These warrants were classified as liabilities as they did not meet the requirements for equity classification under Topic 815, Derivatives and Hedging. These warrants were continually measured at fair value, subject to remeasurement at each balance sheet date.
Inventories	Inventories Inventories are recorded at the lower of cost and net realizable value using the first-in, first-out method. Inventory costs consist primarily of the cost of materials, manufacturing support costs, including labor and factory overhead associated with such production, and shipping costs. The costs of vehicles, charger equipment or prototype products delivered to customers that have not yet met revenue recognition criteria are also included in inventories. The Company assesses the valuation of inventory and periodically records a provision to adjust inventory to its estimated net realizable value, including when the Company determines inventory to be obsolete or in excess of anticipated demand. Once inventory has been written-off or written-down, it creates a new cost basis for the inventory that is not subsequently written-up.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company evaluates the recoverability of property, plant, and equipment and right-of-use assets for possible impairment whenever events or circumstances indicate that the carrying amount of such assets may not be recoverable. Recoverability of these assets is measured by a comparison of the carrying amounts to the future undiscounted cash flows the assets are expected to generate. If such review indicates that the carrying amount of long-lived assets is not recoverable, the carrying amount of such assets is reduced to fair value. In addition to the recoverability assessment, the Company periodically reviews the remaining estimated useful lives of property, plant, and equipment. If the estimated useful life assumption for any asset is reduced, the remaining net book value is depreciated over the revised estimated useful life.
Deferred Revenue and Revenue Recognition	Deferred Revenue Deferred revenue consists of billings or payments received in advance of revenue recognition that are recognized as revenue once the revenue recognition criteria are met. In some instances, progress billings are issued upon meeting certain milestones stated in the contracts. Accordingly, the deferred revenue balance does not represent the total contract value of non-cancelable arrangements. Invoices are typically due within 30 to 40 days. The changes in deferred revenue consisted of the following (in thousands): Deferred revenue as of December 31, 2020 $ 28,221 Revenue recognized from beginning balance during the nine months ended September 30, 2021 (11,774) Deferred revenue added during the nine months ended September 30, 2021 11,101 Deferred revenue as of September 30, 2021 $ 27,548 The current portion of deferred revenue represents the amount that is expected to be recognized as revenue within one year from the balance sheet date. Revenue Recognition The Company derives revenue primarily from the sale of vehicles and charging systems, the installation of charging systems, the sale of battery systems and powertrain components to other vehicle manufacturers, as well as the sale of spare parts and other services provided to customers. Product revenue consists of revenue earned from vehicles and charging systems, battery systems and powertrain components, installation of charging systems, and revenue from leased vehicles, charging systems, and batteries under operating leases. Leasing revenue recognized over time was approximately $0.5 million in each of the three months ended September 30, 2021 and 2020, and $1.6 million and $1.8 million in the nine months ended September 30, 2021 and 2020, respectively. Parts and other service revenue includes revenue earned from spare parts, the design and development of battery systems and drive systems for other vehicle manufacturers, and extended warranties. Goods and services that are promised in the Company’s contracts include vehicles, charging systems, battery systems and powertrain components to other vehicle manufacturers, installation of charging systems, spare parts, and extended warranty. The Company assesses the products and services promised in contracts at contract inception, and identifies performance obligations for each promise to transfer to the customer a product or service that is distinct. If a product or service is separately identifiable from other items in the bundled arrangement and a customer can benefit from the product or service on its own or with other resources that are readily available to the customer, then such product or service is considered distinct. Customer contracts typically have multiple performance obligations. Generally, the Company’s goods and services are considered separate performance obligations. Development services are typically sold on a stand-alone basis and are not bundled with other goods or services. The transaction price of the contract is allocated to each performance obligation in a manner depicting the amount of consideration to which the Company expects to be entitled in exchange for transferring the goods or services to the customer (the “allocation objective”). If the allocation objective is met at contractual prices, no further allocations are made. Otherwise, the Company allocates the transaction price to each performance obligation identified in the contract on a relative standalone selling price basis. To determine the standalone selling price of its promised products or services, the Company conducts an analysis to determine whether its products or services have an observable standalone selling price. In determining the observable standalone selling price, the Company requires that a substantial majority of the standalone selling prices for a product or service fall within a reasonably narrow range. If there is no directly observable standalone selling price for a particular product or service, then the Company estimates a standalone selling price by using the estimated cost plus margin or by reviewing external and internal market factors including, but not limited to, pricing practices including historical discounting, major service groups, and the geographies in which the Company offers products and services. The Company recognizes revenue when or as it satisfies a performance obligation by transferring control of a product or service to a customer. Revenue from product sales is recognized when control of the underlying performance obligations is transferred to the customer. Revenue from vehicles and charging systems, and installation of charging systems is typically recognized upon acceptance by the customer. Under certain contract arrangements, the control of the performance obligations related to the charging systems is transferred over time, and the associated revenue is recognized over the installation period using an input measure based on costs incurred to date relative to total estimated costs to completion. Spare parts revenue is recognized upon shipment. Extended warranty revenue is recognized over the life of the extended warranty using the time elapsed method. Development service contracts typically include the delivery of prototype products to customers. The performance obligation associated with the development of prototype products as well as battery systems and powertrain components to other vehicle manufacturers, is satisfied at a point in time, typically upon shipping. Revenue derived from performance obligations satisfied over time from charging systems and installation was $0.2 million and $1.1 million for the three months ended September 30, 2021 and 2020, respectively, and $5.3 million and $2.3 million for the nine months ended September 30, 2021 and 2020, respectively. Extended warranty revenue is not material to date. As of September 30, 2021 and December 31, 2020, the contract assets balance was $1.3 million and $2.8 million, respectively. The contract assets are expected to be billed within the next twelve months and are recorded in prepaid expenses and other current assets on the balance sheets. As of September 30, 2021, the amount of remaining performance obligations that have not been recognized as revenue was $305.9 million, of which 80% were expected to be recognized as revenue over the next 12 months and the remainder thereafter. This amount excludes the value of remaining performance obligations for contracts with an original expected length of one year or less. While our business has historically been centered on the development and sale of electric transit buses, the increased significance of revenue from Proterra Powered has caused the Company to consider reorganizing into two business units with three business lines, each of which addresses a critical component of the commercial vehicle electrification value proposition in a complementary and self-reinforcing manner: • Proterra Transit designs, develops, manufactures, and sells electric transit buses as an original equipment manufacturer (“OEM”) for North American public transit agencies, airports, universities, and other commercial transit fleets. • Proterra Powered & Energy
Lease Arrangements	Lease Arrangements The Company offers customers leasing alternatives outside of the standard sales contracts for vehicles, charging equipment and batteries used in the vehicles. The leasing arrangements are typically bundled together with the sales contracts. The Company assessed the nature of the bundled arrangements under the revenue accounting standard. For arrangements that contain a lease, the Company determines the classification of the lease in accordance with Topic 842, Leases. A lease arrangement that transfers substantially all of the benefits and risks incident to ownership of the products is classified as a sales-type lease based on the criteria established by the accounting standard; otherwise the lease is classified as an operating lease. For sales-type leases, product revenue is recognized upon customer acceptance of the underlying leased assets. The current portion of net investment in sales-type leases is recorded in Accounts Receivable, and the non-current portion is recorded in Other Assets on the Company’s balance sheets. The discounted unguaranteed residual value of underlying leased assets is not material to the net investment in lease balance. For operating leases, the leasing revenue is recognized on a straight-line basis over the lease term, which is commenced upon customer acceptance. The Company monitors the performance of customers who have leased batteries and are subject to ongoing payments. No allowance was recorded for the receivables under the leasing arrangements.
Product Warranties	Product Warranties The Company provides a limited warranty to customers on vehicles, charging systems, and battery systems. The limited warranty ranges from one
Adoption of New Accounting Standards	ASU No. 2019-12, Income Taxes (Topic 740): Simplifying the Accounting for Income Taxes . This standard simplifies the accounting for income taxes, eliminates certain exceptions within Topic 740, Income Taxes, and clarifies certain aspects of the current guidance to promote consistency among reporting entities. The Company adopted this standard on January 1, 2021, and it had no material impact on the consolidated financial statements. Recent Accounting Pronouncements Not Yet Adopted ASU No. 2020-06, Accounting for Convertible Instruments and Contracts in an Entity’s Own Equity . This standard simplifies the accounting for convertible instruments by removing certain separation models in ASC 470- 20, Debt—Debt with Conversion and Other Options , for convertible instruments. This standard updates the guidance on certain embedded conversion features that are not required to be accounted for as derivatives under Topic 815, Derivatives and Hedging , or that do not result in substantial premiums accounted for as paid-in capital, such that those features are no longer required to be separated from the host contract. The convertible debt instruments will be accounted for as a single liability measured at amortized cost. This will also result in the interest expense recognized for convertible debt instruments to be typically closer to the coupon interest rate when applying the guidance in Topic 835, Interest . Further, this standard made amendments to the EPS guidance in Topic 260 for convertible instruments, the most significant impact of which is requiring the use of the if-converted method for diluted earnings per share calculation, and no longer allowing the net share settlement method. This standard also made revisions to Topic 815-40, which provides guidance on how an entity must determine whether a contract qualifies for a scope exception from derivative accounting. The amendments to Topic 815-40 change the scope of contracts that are recognized as assets or liabilities. This standard is effective for interim and annual periods beginning after December 15, 2021, with early adoption permitted after December 15, 2020. Adoption of this standard can either be on a modified

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	9 Months Ended
	Sep. 30, 2021
Accounting Policies [Abstract]
Concentration of Customer Risk	Revenue Accounts Receivable Three Months Ended September 30, Nine Months Ended September 30, September 30, December 31, 2021 2020 2021 2020 2021 2020 Number of customers accounted for 10% or more* 2 4 — 4 2 2 __________________
Deferred Revenue	The changes in deferred revenue consisted of the following (in thousands): Deferred revenue as of December 31, 2020 $ 28,221 Revenue recognized from beginning balance during the nine months ended September 30, 2021 (11,774) Deferred revenue added during the nine months ended September 30, 2021 11,101 Deferred revenue as of September 30, 2021 $ 27,548
Accrued Warranty Activity	Accrued warranty activity consisted of the following (in thousands): Nine Months Ended September 30, 2021 Warranty reserve - beginning of period $ 18,582 Warranty costs incurred (5,650) Net changes in liability for pre-existing warranties, including expirations (1,663) Provision for warranty 10,243 Warranty reserve - end of period $ 21,512
Revenue of Business Units	The revenue of business units are as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Proterra Transit $ 50,175 $ 30,026 $ 140,187 $ 112,870 Proterra Powered & Energy 11,766 17,511 34,262 29,926 Total $ 61,941 $ 47,537 $ 174,449 $ 142,796
Revenue Disaggregated by Geography	Revenue disaggregated by geography, based on the addresses of our customers, consists of the following (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 United States 59,482 42,709 163,972 104,612 Rest of World 2,459 4,828 10,477 38,184 61,941 47,537 174,449 142,796

Reverse Recapitalization (Table

Reverse Recapitalization (Tables)	9 Months Ended
	Sep. 30, 2021
Reverse Recapitalization [Abstract]
Schedule Of Reverse Recapitalization	The number of shares of Proterra common stock issued immediately following the consummation of the Merger was (in thousands): Shares Ordinary shares Class A of ArcLight, outstanding prior to Merger 27,750 Less redemption of ArcLight shares (15) Sponsor 6,257 Sponsor Earnout Stock 680 Common stock of ArcLight 34,672 PIPE Investors 41,500 Legacy Proterra shares 131,176 Total shares of common stock immediately after Merger 207,348

Fair Value of Financial Instr_2

Fair Value of Financial Instruments (Tables)	9 Months Ended
	Sep. 30, 2021
Fair Value Disclosures [Abstract]
Financial Assets Measured at Fair Value on a Recurring Basis	Financial assets measured at fair value on a recurring basis using the above input categories were as follows (in thousands): Pricing Category Fair Value at September 30, 2021 December 31, 2020 Assets: Cash equivalents and marketable securities: Money market funds Level 1 $ 12,620 $ 744 U.S. Treasury securities Level 1 199,920 64,997 Short-term investments: U.S. Treasury securities Level 1 261,068 68,990 Corporate debt securities Level 1 185,883 — Total $ 659,491 $ 134,731 Liabilities: Other non-current liabilities Derivative liability Level 3 $ — $ 70,870 Legacy Proterra warrant liability Level 3 — 39,670 Public warrant liability Level 1 36,352 — Private placement warrant liability Level 2 19,781 — Total $ 56,133 $ 110,540
Contractual Maturities of Short-Term Investments	The contractual maturities of short-term investments are as follows (in thousands): September 30, 2021 December 31, 2020 Due within one year $ 296,934 $ 68,990 Due after one year to two years 150,017 — Total $ 446,951 $ 68,990
Changes in Fair Value of Derivative and Warrant Liabilities	A summary of the changes of the derivative liability and warrant liabilities is as follows (in thousands): Derivative liability Legacy Proterra warrant liability Private placement warrant liability Public warrant liability Fair value as of December 31, 2020 $ 70,870 $ 39,670 $ — $ — Warrant liability acquired as part of the reverse recapitalization — — 57,610 84,640 Change in fair value 111,684 47,346 (37,829) (48,288) Reclassification of liability upon exercise of warrants — (17,696) — — Reclassification of liability upon the reverse recapitalization (182,554) (69,320) — — Fair value as of September 30, 2021 $ — $ — $ 19,781 $ 36,352

Balance Sheet Components (Table

Balance Sheet Components (Tables)	9 Months Ended
	Sep. 30, 2021
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Cash and Cash Equivalents	Cash and cash equivalents consisted of the following (in thousands): September 30, 2021 December 31, 2020 Cash $ 67,924 $ 44,978 Cash equivalents 212,613 65,741 Total cash and cash equivalents $ 280,537 $ 110,719 The following table provides a reconciliation of cash, cash equivalents, and restricted cash reported within the balance sheets to the total of such amounts shown on the statements of cash flows. September 30, 2021 December 31, 2020 Cash and cash equivalents $ 280,537 $ 110,719 Restricted cash, current portion 10,890 8,397 Restricted cash, net of current portion 1,675 4,581 Total restricted cash 12,565 12,978 Total cash and cash equivalents, and restricted cash $ 293,102 $ 123,697
Inventories	Inventories consisted of the following (in thousands): September 30, 2021 December 31, 2020 Raw materials $ 49,880 $ 31,148 Work in progress 27,033 8,042 Finished goods 19,561 47,756 Service parts 6,221 5,384 Total inventories $ 102,695 $ 92,330
Property, Plant and Equipment, Net	Property, plant, and equipment, net, consisted of the following (in thousands): September 30, 2021 December 31, 2020 Computer hardware $ 5,099 $ 4,708 Computer software 9,445 8,849 Internally used vehicles and charging systems 19,260 19,136 Leased vehicles and batteries 7,027 7,081 Leasehold improvements 10,459 10,234 Machinery and equipment 24,995 26,026 Office furniture and equipment 1,859 1,854 Tooling 20,782 21,727 Finance lease right-of-use assets 179 179 Construction in progress 10,634 1,830 109,739 101,624 Less: Accumulated depreciation and amortization (56,680) (48,037) Total $ 53,059 $ 53,587
Accrued Liabilities	Accrued liabilities consisted of the following (in thousands): September 30, 2021 December 31, 2020 Accrued payroll and related expenses $ 6,827 $ 6,695 Accrued sales and use tax 1,075 975 Warranty reserve 8,117 6,121 Financing obligation 2,346 3,056 Accrued audit and accounting related expenses 683 428 Accrued charger installation costs 1,020 769 Accrued legal expenses 312 510 Other accrued expenses 2,680 1,182 Total $ 23,060 $ 19,736
Other Long-term Liabilities	Other long-term liabilities consisted of the following (in thousands): September 30, 2021 December 31, 2020 Warranty reserve $ 13,395 $ 12,461 Finance lease liabilities, non-current 95 117 Total $ 13,490 $ 12,578

Debt (Tables)

Debt (Tables)	9 Months Ended
	Sep. 30, 2021
Debt Disclosure [Abstract]
Debt	Debt, net of debt discount and issuance costs, consisted of the following (in thousands): September 30, 2021 December 31, 2020 Senior Credit Facility $ — $ 16,809 PPP loan 10,000 10,000 Convertible Notes 95,896 106,443 Total debt 105,896 133,252 Less debt, current 10,000 — Debt, non-current $ 95,896 $ 133,252
Convertible Notes	The Convertible Notes, net of debt discount and issuance costs, consisted of the following (in thousands): September 30, 2021 December 31, 2020 Principal $ 153,500 $ 200,000 PIK interest 7,994 3,501 Total principal 161,494 203,501 Less debt discount and issuance costs (65,598) (97,058) Total Convertible Notes $ 95,896 $ 106,443
Contractual Future Principal Repayments of Debt	As of September 30, 2021, the contractual future principal repayments of the total debt were as follows (in thousands): 2022 $ 10,000 2025 (1) 161,494 Total debt $ 171,494 __________________

Leases (Tables)

Leases (Tables)	9 Months Ended
	Sep. 30, 2021
Leases [Abstract]
Net Investment in Leases	The net investment in leases consisted of the following (in thousands): September 30, 2021 December 31, 2020 Net investment in leases, current $ 411 $ 398 Net investment in leases, non-current 4,838 3,101 Total net investment in leases $ 5,249 $ 3,499
Future Minimum Payments Receivable from Operating Leases	Future minimum payments receivable from operating and sales-type leases as of September 30, 2021 for each of the next five years are as follows: Operating leases Sales-type leases Remainder of 2021 $ — $ 99 2022 — 395 2023 — 469 2024 — 485 2025 — 758 Thereafter — 3,592 Total minimum lease payments $ — $ 5,798
Future Minimum Payments Receivable from Sales-Type Leases	Future minimum payments receivable from operating and sales-type leases as of September 30, 2021 for each of the next five years are as follows: Operating leases Sales-type leases Remainder of 2021 $ — $ 99 2022 — 395 2023 — 469 2024 — 485 2025 — 758 Thereafter — 3,592 Total minimum lease payments $ — $ 5,798
Maturities of Operating Lease Liabilities	Maturities of operating lease liabilities as of September 30, 2021 were as follows (in thousands): Remainder of 2021 $ 1,036 2022 3,650 2023 2,808 2024 1,685 2025 1,039 Thereafter 443 Total undiscounted lease payment 10,661 Less: imputed interest (775) Total operating lease liabilities $ 9,886
Supplemental Cash Flow Information	Supplemental cash flow information related to leases were as follows (in thousands): Nine Months Ended September 30, 2021 2020 Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows for operating leases $ (3,050) $ (1,901)
Operating Lease Right-Of-Use Assets and Liabilities	Operating lease right-of-use assets and liabilities consist of the following (in thousands): September 30, 2021 December 31, 2020 Operating leases Operating lease right-of-use assets $ 9,234 $ 10,310 Operating lease liabilities, current 3,583 3,153 Operating lease liabilities, non-current 6,303 7,891 Total operating lease liabilities $ 9,886 $ 11,044

Stockholders' Equity (Tables)

Stockholders' Equity (Tables)	9 Months Ended
	Sep. 30, 2021
Equity [Abstract]
Reserved Shares of Common Stock	The Company had reserved shares of common stock for issuance as follows (in thousands): September 30, 2021 2010 Equity Incentive Plan 21,654 2021 Equity Incentive Plan 10,591 2021 Employee Stock Purchase Plan 1,630 Warrants 24,862 Earnout Stock 18,009 Total 76,746

Warrants (Tables)

Warrants (Tables)	9 Months Ended
	Sep. 30, 2021
Other Liabilities Disclosure [Abstract]
Activity of Warrants	Activity of warrants in the nine months period ended September 30, 2021 is as follows: Public warrants Private placement warrants Other warrants Total warrants Outstanding as of December 31, 2020 — — 5,104,030 5,104,030 Issued as part of the Merger 13,874,994 7,550,000 — 21,424,994 Exercised 1 — — (1,681,236) (1,681,236) Outstanding as of September 30, 2021 13,874,994 7,550,000 3,422,794 24,847,788 __________________ 1. Certain warrant holders elected to net exercise their warrants, and as a result, an aggregate of 1,564,958 shares of common stock were issued.

Equity Plans and Stock-based _2

Equity Plans and Stock-based Compensation (Tables)	9 Months Ended
	Sep. 30, 2021
Share-based Payment Arrangement [Abstract]
Stock Option Activity	A summary of the Company’s stock option activity and related information was as follows: Options Outstanding Number of Stock Options Outstanding Weighted- Average Exercise Price Weighted-Average Remaining Contractual Life Aggregate Intrinsic Value (in thousands) Balance as of December 31, 2020 (1) 20,178,784 3.81 7.4 $ 65,056 Granted 674,643 9.86 Exercised (1,676,533) 3.24 Cancelled/forfeited/expired (513,463) 5.09 Balance as of September 30, 2021 (2) 18,663,431 4.04 6.9 $ 113,302 Exercisable as of September 30, 2021 (3) 12,592,271 3.35 6.0 $ 85,124 __________________ (1) Excluding Equity Awards of 2,677,500 shares and Milestone Options of 669,375 shares outstanding, of which 502,031 shares vested and exercisable as of December 31, 2020. Refer to section below for further details. (2) Excluding Equity Awards of 2,677,500 shares and Milestone Options of 669,375 shares outstanding as of September 30, 2021. (3) Excluding 1,004,064 shares exercisable under the Equity Awards with weighted average exercise price of $19.61 per share as of September 30, 2021.
Assumptions for Fair Value of Stock Options	The fair value of stock options granted is estimated on the date of grant using the following assumptions: Nine Months Ended September 30, 2021 2020 Expected term (in years) 6.2 6.0 Risk-free interest rate 1.0 % 0.5 % Expected volatility 53.9 % 73.1 % Expected dividend rate — —
RSU Activity	A summary of the Company's RSU activity and related information is as follows: Number of RSUs Weighted Average Grant Date Fair Value Aggregate Intrinsic Value Balance as of December 31, 2020 — $ — $ — Granted 857,199 11.33 Vested — — Forfeited (9,441) 11.33 Balance as of September 30, 2021 847,758 $ 11.33 $ 8,571
Stock-Based Compensation Expense	Stock-based compensation expense included in operating results was as follows (in thousands): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Cost of goods sold $ 319 $ 235 $ 865 $ 688 Research and development 567 461 1,625 1,183 Selling, general and administrative 2,292 1,984 8,775 5,680 Total stock-based compensation expense $ 3,178 $ 2,680 $ 11,265 $ 7,551

Net Income (Loss) Per Share (Ta

Net Income (Loss) Per Share (Tables)	9 Months Ended
	Sep. 30, 2021
Earnings Per Share [Abstract]
Computation of Basic and Diluted Net Loss Per Share	The computation of the Company’s basic and diluted net income (loss) per share of common stock attributable to common stockholders was as follows (in thousands, except for per share data): Three Months Ended September 30, Nine Months Ended September 30, 2021 2020 2021 2020 Numerator: Net income (loss) $ 36,321 $ (46,860) $ (204,868) $ (94,384) Effect of dilutive securities: Gain on valuation of warrant liabilities (73,197) — — — Interest expense to be recognized upon conversion of Convertible Notes (1) (61,774) — — — Numerator for diluted EPS - Net loss after the effect of dilutive securities $ (98,650) $ (46,860) $ (204,868) $ (94,384) Denominator: Basic weighted average shares (2) 212,071 4,406 89,233 4,139 Dilutive impact of public and private placement warrants 594 — — — Convertible Notes (1) 24,300 — — — Diluted weighted average shares 236,965 4,406 89,233 4,139 Net income (loss) per share of common stock: Basic $ 0.17 $ (10.64) $ (2.30) $ (22.80) Diluted $ (0.42) $ (10.64) $ (2.30) $ (22.80) _____________ (1) Adjustment is under the “if-converted” method, and includes write-off of $68.8 million unamortized debt discount of the Convertible Notes as of June 30, 2021, offset by the $7.0 million interest expense recorded in net income of the third quarter of 2021. (2) Includes the remaining outstanding warrants issued in connection with the Convertible Notes with an exercise price of $0.02 per share as of the Closing Date. The exercise of these warrants is virtually assured based on common stock trading price since the Closing Date. Therefore, the outstanding shares are included in the denominator of both the basic and diluted EPS calculation. In addition, prior to the Closing Date, such warrants were liability classified, and accordingly excluded from EPS calculation.
Potentially Dilutive Securities Excluded from the Diluted Per Share Calculation	The potentially dilutive securities were as follows (in thousands): September 30, 2021 Stock options and RSUs 22,858 Other warrants to purchase common stock 1 22,859

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)business_unitsegmentbusiness_line	Oct. 29, 2021$ / shares	Sep. 27, 2021$ / shares	Jun. 14, 2021	Dec. 31, 2020USD ($)
Accounting Policies [Abstract]
Common stock exchange ratio				0.8925
Subsequent Event [Line Items]
Redemption price (in dollars per share) | $ / shares			$ 0.10
Number of business units | business_unit	2
Number of business lines | business_line	3
Accumulated deficit	$ 813,087				$ 608,219
Cash and cash equivalents and short-term investments	$ 727,500
Number of reportable segments | segment	1
Restricted cash	$ 12,565				$ 12,978
Subsequent event
Subsequent Event [Line Items]
Redemption price (in dollars per share) | $ / shares		$ 0.10

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Revenue Disaggregated by Geography (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 61,941	$ 47,537	$ 174,449	$ 142,796
United States
Disaggregation of Revenue [Line Items]
Total revenue	59,482	42,709	163,972	104,612
Rest of World
Disaggregation of Revenue [Line Items]
Total revenue	$ 2,459	$ 4,828	$ 10,477	$ 38,184

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Credit Risk and Concentration (Details) - Customer Concentration Risk - customer	3 Months Ended		9 Months Ended		12 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Revenue Benchmark
Concentration Risk [Line Items]
Number of customers accounted for 10% or more	2	4	0	4
Accounts Receivable
Concentration Risk [Line Items]
Number of customers accounted for 10% or more			2		2
Accounts Receivable | One Customer
Concentration Risk [Line Items]
Concentration risk percentage					33.00%

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Fair Value of Financial Instruments (Details)	1 Months Ended
	Sep. 30, 2020USD ($)
ArcLight Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)	$ 21,425,000
ArcLight Public Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)	13,875,000
ArcLight Private Placement Warrants
Class of Warrant or Right [Line Items]
Warrants issued (in shares)	$ 7,550,000

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Deferred Revenue (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Change In Contract With Customer, Asset and Liability [Roll Forward]
Deferred revenue	$ 28,221
Revenue recognized from beginning balance during the nine months ended September 30, 2021	(11,774)
Deferred revenue added during the nine months ended September 30, 2021	11,101
Deferred revenue	$ 27,548

Summary of Significant Accoun_9

Summary of Significant Accounting Policies - Revenue Recognition (Details) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021USD ($)	Sep. 30, 2020USD ($)	Sep. 30, 2021USD ($)business_unitbusiness_line	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Disaggregation of Revenue [Line Items]
Leasing revenue	$ 500	$ 500	$ 1,600	$ 1,800
Total revenue	61,941	47,537	174,449	142,796
Contract assets	1,300		1,300		$ 2,800
Remaining performance obligation	$ 305,900		$ 305,900
Number of business units | business_unit			2
Number of business lines | business_line			3
Revenue, Remaining Performance Obligation, Expected Timing of Satisfaction, Start Date [Axis]: 2021-10-01
Disaggregation of Revenue [Line Items]
Remaining performance obligation, percentage	80.00%		80.00%
Remaining performance obligation, term	12 months		12 months
Charging systems and installation
Disaggregation of Revenue [Line Items]
Total revenue	$ 200	$ 1,100	$ 5,300	$ 2,300

Summary of Significant Accou_10

Summary of Significant Accounting Policies - Revenue of Business Units (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Disaggregation of Revenue [Line Items]
Total revenue	$ 61,941	$ 47,537	$ 174,449	$ 142,796
Proterra Transit
Disaggregation of Revenue [Line Items]
Total revenue	50,175	30,026	140,187	112,870
Proterra Powered & Energy
Disaggregation of Revenue [Line Items]
Total revenue	$ 11,766	$ 17,511	$ 34,262	$ 29,926

Summary of Significant Accou_11

Summary of Significant Accounting Policies - Product Warranties (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Movement in Standard Product Warranty Accrual [Roll Forward]
Warranty reserve - beginning of period	$ 18,582
Warranty costs incurred	(5,650)
Net changes in liability for pre-existing warranties, including expirations	(1,663)
Provision for warranty	10,243
Warranty reserve - end of period	$ 21,512
Minimum
Product Warranty Liability [Line Items]
Product warranty term	1 year
Maximum
Product Warranty Liability [Line Items]
Product warranty term	12 years

Reverse Recapitalization - Narr

Reverse Recapitalization - Narrative (Details) $ / shares in Units, $ in Thousands	Jun. 14, 2021USD ($)lease$ / sharesshares	Jul. 31, 2021shares	Sep. 30, 2021USD ($)shares	Sep. 30, 2020USD ($)	Jun. 13, 2021$ / sharesshares	Dec. 31, 2020shares
Schedule Of Reverse Recapitalization [Line Items]
Common stock exchange ratio	0.8925
Stock converted (in shares)	123,752,882
Debt amount converted | $			$ 48,607	$ 0
Conversion of convertible securities (in shares)			1,564,958
Common stock reserved for issuance (in shares)	22,532,619		76,746,000
Stock converted (in shares)	34,671,900
Warrants converted (in shares)	21,424,994
Convertible securities, period from merger closing	5 years
Convertible securities, additional common stock issuable (shares)	22,809,500
Threshold trading days | lease	20
Threshold consecutive trading days | lease	30
Stock price threshold for additional common stock issuable (in dollars per share) | $ / shares	$ 15
Stock price threshold for additional common stock issuable, change of control (in dollars per share) | $ / shares	$ 15
Merger Agreement, sponsor stock minimum percentage	10.00%
Common stock, shares outstanding (in shares)	207,348,000		212,827,249			5,678,000
Additional shares issuable, term	5 years
Capital stock, shares authorized (in shares)	510,000,000				271,920,636
Capital stock, par value (in dollars per share) | $ / shares	$ 0.0001				$ 0.0001
Common stock, shares authorized (in shares)	500,000,000		500,000,000		156,276,750	156,277,000
Preferred stock, shares authorized (in shares)	10,000,000		10,000,000		115,643,886	0
Common stock, shares issued (in shares)	207,300,000		212,827,249			5,678,000
Preferred stock, shares issued (in shares)	0		0			0
Preferred stock, shares outstanding (in shares)	0		0			0
Warrant to purchase shares of convertible preferred stock (in shares)	24,900,000
Aggregate cash proceeds received, net | $	$ 649,300
PIPE investment fees | $	13,800
Transaction costs | $	18,500
Deferred underwriting fees payable | $	9,700
Other accrued expenses | $	1,300
Related party payable | $	$ 100
Deferred transaction costs | $			$ 2,900
Reverse Recapitalization, Additional Common Shares Issuable Scenario One
Schedule Of Reverse Recapitalization [Line Items]
Percentage of additional common stock issuable	21.0526%
Stock price threshold for additional common stock issuable (in dollars per share) | $ / shares	$ 15
Stock price threshold for additional common stock issuable, change of control (in dollars per share) | $ / shares	$ 15
Reverse Recapitalization, Additional Common Shares Issuable Scenario Two
Schedule Of Reverse Recapitalization [Line Items]
Percentage of additional common stock issuable	26.3158%
Stock price threshold for additional common stock issuable (in dollars per share) | $ / shares	$ 20
Stock price threshold for additional common stock issuable, change of control (in dollars per share) | $ / shares	$ 20
Reverse Recapitalization, Additional Common Shares Issuable Scenario Three
Schedule Of Reverse Recapitalization [Line Items]
Percentage of additional common stock issuable	26.3158%
Stock price threshold for additional common stock issuable (in dollars per share) | $ / shares	$ 25
Stock price threshold for additional common stock issuable, change of control (in dollars per share) | $ / shares	$ 25
Reverse Recapitalization, Additional Common Shares Issuable Scenario Four
Schedule Of Reverse Recapitalization [Line Items]
Percentage of additional common stock issuable	26.3158%
Stock price threshold for additional common stock issuable (in dollars per share) | $ / shares	$ 30
Stock price threshold for additional common stock issuable, change of control (in dollars per share) | $ / shares	$ 30
Milestone Options
Schedule Of Reverse Recapitalization [Line Items]
Number of shares that fully vested (in shares)	669,375
Legacy warrants
Schedule Of Reverse Recapitalization [Line Items]
Common stock reserved for issuance (in shares)	3,504,523
Public warrants
Schedule Of Reverse Recapitalization [Line Items]
Warrant to purchase shares of convertible preferred stock (in shares)	13,900,000
Private placement warrants
Schedule Of Reverse Recapitalization [Line Items]
Warrant to purchase shares of convertible preferred stock (in shares)	7,600,000
Proterra warrants
Schedule Of Reverse Recapitalization [Line Items]
Warrant to purchase shares of convertible preferred stock (in shares)	3,500,000
2021 Equity Incentive Plan
Schedule Of Reverse Recapitalization [Line Items]
Common stock reserved for issuance (in shares)	10,400,000		10,591,000
2010 Equity Incentive Plan
Schedule Of Reverse Recapitalization [Line Items]
Common stock reserved for issuance (in shares)	22,500,000		21,654,000
Employee Stock Purchase Plan
Schedule Of Reverse Recapitalization [Line Items]
Common stock reserved for issuance (in shares)	1,600,000
Common Stock
Schedule Of Reverse Recapitalization [Line Items]
Conversion of convertible securities (in shares)	7,400,000
Stock Options, Warrants, and Contingent Shares
Schedule Of Reverse Recapitalization [Line Items]
Common stock reserved for issuance (in shares)	82,300,000
Proterra Common Stock
Schedule Of Reverse Recapitalization [Line Items]
Stock issued, contingent consideration (in shares)		4,800,563
Sponsor Contingent Shares
Schedule Of Reverse Recapitalization [Line Items]
Stock issued, contingent consideration (in shares)		679,750
ArcLight
Schedule Of Reverse Recapitalization [Line Items]
Number of shares redeemed (in shares)	15,172
Value of stocks redeemed | $	$ 200
Common stock, shares outstanding (in shares)					27,750,000
Convertible Notes
Schedule Of Reverse Recapitalization [Line Items]
Debt amount converted | $	$ 46,500
ArcLight board of directors
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)	140,000
PIPE offering
Schedule Of Reverse Recapitalization [Line Items]
Issuance of stock (in shares)	41,500,000
Issuance of stock, price (in dollars per share) | $ / shares	$ 10
Issuance of stock, proceeds | $	$ 415,000

Reverse Recapitalization - Shar

Reverse Recapitalization - Shares Issued in Merger (Details) - shares	Jun. 14, 2021	Jun. 13, 2021	Sep. 30, 2021	Dec. 31, 2020
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)	207,348,000		212,827,249	5,678,000
Sponsor	6,257,000
Sponsor Earnout Stock	680,000
ArcLight Shareholders
Schedule Of Reverse Recapitalization [Line Items]
Issuance of stock (in shares)	34,672,000
PIPE Investors
Schedule Of Reverse Recapitalization [Line Items]
Issuance of stock (in shares)	41,500,000
Legacy Proterra Investors
Schedule Of Reverse Recapitalization [Line Items]
Issuance of stock (in shares)	131,176,000
ArcLight
Schedule Of Reverse Recapitalization [Line Items]
Common stock, shares outstanding (in shares)		27,750,000
Less redemption of ArcLight shares		(15,000)

Fair Value of Financial Instr_3

Fair Value of Financial Instruments - Schedule of Financial Assets Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Jun. 13, 2021	Dec. 31, 2020
Assets:
Short-term investments	$ 446,951		$ 68,990
Total	659,491		134,731
Other non-current liabilities
Warrant liability	56,133		39,670
Public warrants
Other non-current liabilities
Warrant liability		$ 84,600
Private placement warrants
Other non-current liabilities
Warrant liability		$ 57,600
Fair Value, Recurring
Other non-current liabilities
Total	56,133		110,540
Fair Value, Recurring | Level 1 | U.S. Treasury securities
Assets:
Short-term investments	261,068		68,990
Fair Value, Recurring | Level 1 | Corporate debt securities
Assets:
Short-term investments	185,883		0
Fair Value, Recurring | Level 1 | Public warrants
Other non-current liabilities
Warrant liability	36,352		0
Fair Value, Recurring | Level 3
Other non-current liabilities
Derivative liability	0		70,870
Fair Value, Recurring | Level 3 | Legacy Proterra warrants
Other non-current liabilities
Warrant liability	0		39,670
Fair Value, Recurring | Level 2 | Private placement warrants
Other non-current liabilities
Warrant liability	19,781		0
Money market funds | Fair Value, Recurring | Level 1
Assets:
Cash equivalents and marketable securities	12,620		744
U.S. Treasury securities | Fair Value, Recurring | Level 1
Assets:
Cash equivalents and marketable securities	$ 199,920		$ 64,997

Fair Value of Financial Instr_4

Fair Value of Financial Instruments - Contractual Maturities of Short-Term Investments (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Fair Value Disclosures [Abstract]
Due within one year	$ 296,934	$ 68,990
Due after one year to two years	150,017	0
Total	$ 446,951	$ 68,990

Fair Value of Financial Instr_5

Fair Value of Financial Instruments - Narrative (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Warrant, expiration period, period from qualified IPO	5 years
Convertible Notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Unamortized debt discount and issuance costs	$ 65,598	$ 97,058
Convertible Notes | Fair value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible debt	303,400
Convertible Notes | Carrying value
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Convertible debt	$ 95,900

Fair Value of Financial Instr_6

Fair Value of Financial Instruments - Changes in Fair Value of Derivative and Warrant Liabilities (Details) $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)
Derivative liability
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value	$ 70,870
Warrant liability acquired as part of the reverse recapitalization	0
Change in fair value	111,684
Reclassification of liability upon exercise of warrants	0
Reclassification of liability upon the reverse recapitalization	(182,554)
Fair value	0
Warrant liability | Legacy Proterra warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value	39,670
Warrant liability acquired as part of the reverse recapitalization	0
Change in fair value	47,346
Reclassification of liability upon exercise of warrants	(17,696)
Reclassification of liability upon the reverse recapitalization	(69,320)
Fair value	0
Warrant liability | Private placement warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value	0
Warrant liability acquired as part of the reverse recapitalization	57,610
Change in fair value	(37,829)
Reclassification of liability upon exercise of warrants	0
Reclassification of liability upon the reverse recapitalization	0
Fair value	19,781
Warrant liability | Public warrants
Fair Value, Liabilities Measured on Recurring Basis, Unobservable Input Reconciliation, Calculation [Roll Forward]
Fair value	0
Warrant liability acquired as part of the reverse recapitalization	84,640
Change in fair value	(48,288)
Reclassification of liability upon exercise of warrants	0
Reclassification of liability upon the reverse recapitalization	0
Fair value	$ 36,352

Balance Sheet Components - Cash

Balance Sheet Components - Cash and Cash Equivalents, and Restricted Cash (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020	Sep. 30, 2020	Dec. 31, 2019
Cash and Cash Equivalents
Cash	$ 67,924	$ 44,978
Cash equivalents	212,613	65,741
Total cash and cash equivalents	280,537	110,719
Cash, Cash Equivalents and Restricted Cash
Cash and cash equivalents	280,537	110,719
Restricted cash, current portion	10,890	8,397
Restricted cash, net of current portion	1,675	4,581
Total restricted cash	12,565	12,978
Total cash and cash equivalents, and restricted cash	$ 293,102	$ 123,697	$ 152,036	$ 53,649

Balance Sheet Components - Inve

Balance Sheet Components - Inventories (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Raw materials	$ 49,880		$ 49,880		$ 31,148
Work in progress	27,033		27,033		8,042
Finished goods	19,561		19,561		47,756
Service parts	6,221		6,221		5,384
Total inventories	102,695		102,695		$ 92,330
Write-down of inventories	$ 600	$ 700	$ 1,300	$ 2,500

Balance Sheet Components - Prop

Balance Sheet Components - Property, Plant and Equipment (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Property, Plant and Equipment [Line Items]
Finance lease right-of-use assets	$ 179		$ 179		$ 179
Property, plant and equipment, and finance lease right-of-use asset gross	109,739		109,739		101,624
Less: Accumulated depreciation and amortization	(56,680)		(56,680)		(48,037)
Total	53,059		53,059		53,587
Reimbursable equipment costs			1,400
Depreciation and amortization expense	3,900	$ 3,700	11,675	$ 11,493
Computer hardware
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	5,099		5,099		4,708
Computer software
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	9,445		9,445		8,849
Internally used vehicles and charging systems
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	19,260		19,260		19,136
Leased vehicles and batteries
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	7,027		7,027		7,081
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	10,459		10,459		10,234
Machinery and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	24,995		24,995		26,026
Office furniture and equipment
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	1,859		1,859		1,854
Tooling
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	20,782		20,782		21,727
Construction in progress
Property, Plant and Equipment [Line Items]
Property, plant and equipment, gross	$ 10,634		$ 10,634		$ 1,830

Balance Sheet Components - Accr

Balance Sheet Components - Accrued Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Accrued payroll and related expenses	$ 6,827	$ 6,695
Accrued sales and use tax	1,075	975
Warranty reserve	8,117	6,121
Financing obligation	2,346	3,056
Accrued audit and accounting related expenses	683	428
Accrued charger installation costs	1,020	769
Accrued legal expenses	312	510
Other accrued expenses	2,680	1,182
Total	$ 23,060	$ 19,736

Balance Sheet Components - Othe

Balance Sheet Components - Other Long-Term Liabilities (Details) - USD ($) $ in Thousands	1 Months Ended
	Jul. 31, 2016	Sep. 30, 2021	Dec. 31, 2020
Organization, Consolidation and Presentation of Financial Statements [Abstract]
Warranty reserve		$ 13,395	$ 12,461
Finance lease liabilities, non-current		95	117
Total		13,490	12,578
Financing obligation, term	5 years
Financing obligation	$ 6,000	$ 2,300	$ 3,100

Debt (Details)

Debt (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Total debt	$ 105,896	$ 133,252
Less debt, current	10,000	0
Debt, non-current	95,896	133,252
Senior Credit Facility
Debt Instrument [Line Items]
Total debt	0	16,809
PPP loan
Debt Instrument [Line Items]
Total debt	10,000	10,000
Convertible Notes
Debt Instrument [Line Items]
Total debt	$ 95,896	$ 106,443

Debt - Senior Credit Facility (

Debt - Senior Credit Facility (Details) - USD ($)	1 Months Ended
	Jun. 30, 2021	May 31, 2019	Sep. 30, 2021	Dec. 31, 2020
Debt Instrument [Line Items]
Amount outstanding			$ 105,896,000	$ 133,252,000
Letters of credit outstanding, amount			10,500,000
Senior Credit Facility
Debt Instrument [Line Items]
Amount outstanding			0	16,809,000
Senior Credit Facility
Debt Instrument [Line Items]
Borrowing capacity		$ 75,000,000
Availability, period from maturity of subordinated debt		91 days
Availability, subordinated debt		$ 7,500,000
Commitment potential increase		50,000,000
Commitment potential reduction		$ 25,000,000
Termination notice period		15 days
Fixed Charge Coverage Ratio		1
Amount outstanding			0	$ 17,100,000
Interest rate				3.09%
Repayments of lines of credit	$ 17,100,000
Unamortized debt issuance costs			200,000
Letters of credit outstanding, amount			$ 10,400,000
Senior Credit Facility | Federal Funds Rate | Variable rate component one
Debt Instrument [Line Items]
Spread on variable interest rate		0.50%
Senior Credit Facility | London Interbank Offered Rate (LIBOR) | Variable rate component one
Debt Instrument [Line Items]
Spread on variable interest rate		1.00%
Senior Credit Facility | London Interbank Offered Rate (LIBOR) | Minimum | Variable rate component two
Debt Instrument [Line Items]
Spread on variable interest rate		1.50%
Senior Credit Facility | London Interbank Offered Rate (LIBOR) | Maximum | Variable rate component two
Debt Instrument [Line Items]
Spread on variable interest rate		3.00%
Senior Credit Facility | Base Rate | Minimum | Variable rate component two
Debt Instrument [Line Items]
Spread on variable interest rate		0.00%
Senior Credit Facility | Base Rate | Maximum | Variable rate component two
Debt Instrument [Line Items]
Spread on variable interest rate		1.50%
Letter of credit
Debt Instrument [Line Items]
Borrowing capacity		$ 15,000,000

Debt - Small Business Administr

Debt - Small Business Administration Loan (Details) - USD ($) $ in Thousands	1 Months Ended	9 Months Ended
	May 31, 2020	Sep. 30, 2021	Sep. 30, 2020
Debt Instrument [Line Items]
Loan proceeds		$ 0	$ 224,047
PPP loan
Debt Instrument [Line Items]
Loan proceeds	$ 10,000

Debt - Convertible Notes (Detai

Debt - Convertible Notes (Details)	Jun. 14, 2021USD ($)shares	Aug. 31, 2020USD ($)lease$ / sharesshares	Sep. 30, 2021USD ($)$ / shares	Sep. 30, 2020USD ($)	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)$ / shares	Sep. 30, 2020USD ($)	Dec. 31, 2020USD ($)
Debt Instrument [Line Items]
Warrant to purchase shares of convertible preferred stock (in shares) | shares	24,900,000
Exercise price of warrants (in dollars per share) | $ / shares			$ 11.50			$ 11.50
Warrant liability			$ 56,133,000			$ 56,133,000		$ 39,670,000
Debt amount converted						48,607,000	$ 0
Conversion of Convertible Notes into common stock						48,781,000
Amortization of debt issuance cost and debt discounts						31,519,000	2,342,000
Convertible Debt [Abstract]
Total debt			105,896,000			105,896,000		133,252,000
Additional Paid-in Capital
Debt Instrument [Line Items]
Conversion of Convertible Notes into common stock						48,780,000
Convertible note warrants
Debt Instrument [Line Items]
Warrant to purchase shares of convertible preferred stock (in shares) | shares		4,600,000
Exercise price of warrants (in dollars per share) | $ / shares		$ 0.02
Warrants term		7 years
Warrant liability		$ 29,000,000
Warrants term from issuance date		5 years
Fair value of embedded derivative liability		$ 68,500,000
Convertible Notes
Debt Instrument [Line Items]
Aggregate principal amount		$ 200,000,000
Interest rate		5.00%
Paid-in-kind interest rate		4.50%
Threshold consecutive trading days | lease		20
Conversion terms, threshold percentage of stock price trigger		150.00%
Stock price trigger (in dollars per share) | $ / shares		$ 9.86
Conversion terms, event of liquidation or sale, conversion price percentage		150.00%
Covenant, required minimum liquidity		$ 75,000,000
Covenant, required minimum liquidity, multiple factor of cash burn		4
Debt issuance costs incurred		$ 5,100,000
Debt amount converted	$ 46,500,000
Write off of unamortized debt issuance cost	21,000,000				$ 68,800,000
Amortization of debt issuance cost and debt discounts			3,200,000	$ 1,900,000		31,500,000	$ 1,900,000
Convertible Debt [Abstract]
Principal			153,500,000			153,500,000		200,000,000
PIK interest			7,994,000			7,994,000		3,501,000
Total principal			161,494,000			161,494,000		203,501,000
Less debt discount and issuance costs			(65,598,000)			(65,598,000)		(97,058,000)
Total debt			$ 95,896,000			$ 95,896,000		$ 106,443,000
Convertible Notes | Additional Paid-in Capital
Debt Instrument [Line Items]
Conversion of Convertible Notes into common stock	$ 48,800,000

Debt - Future Principal Repayme

Debt - Future Principal Repayments (Details) $ in Thousands	Sep. 30, 2021USD ($)
Debt Disclosure [Abstract]
2022	$ 10,000
2025	161,494
Total debt	$ 171,494

Leases - Narrative (Details)

Leases - Narrative (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Leases [Abstract]
Cash proceeds from lease payment, operating activity			$ 1.2
Operating lease, product revenue			0.4
Operating lease, expense	$ 1	$ 1	3	$ 3
Operating lease right-of-use assets obtained in exchange for lease liabilities			$ 1.5
Operating lease, weighted average remaining lease term	3 years 3 months 18 days		3 years 3 months 18 days
Operating lease, weighted average discount rate, percent	4.60%		4.60%

Leases - Net Investment In Leas

Leases - Net Investment In Lease (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Net investment in leases, current	$ 411	$ 398
Net investment in leases, non-current	4,838	3,101
Total net investment in leases	$ 5,249	$ 3,499

Leases - Lessor Future Minimum

Leases - Lessor Future Minimum Payments Receivable (Details) $ in Thousands	Sep. 30, 2021USD ($)
Operating leases
Remainder of 2021	$ 0
2022	0
2023	0
2024	0
2025	0
Thereafter	0
Total minimum lease payments	0
Sales-type leases
Remainder of 2021	99
2022	395
2023	469
2024	485
2025	758
Thereafter	3,592
Total minimum lease payments	$ 5,798

Leases - Maturities Of Operatin

Leases - Maturities Of Operating Lease Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Leases [Abstract]
Remainder of 2021	$ 1,036
2022	3,650
2023	2,808
2024	1,685
2025	1,039
Thereafter	443
Total undiscounted lease payment	10,661
Less: imputed interest	(775)
Total operating lease liabilities	$ 9,886	$ 11,044

Leases - Supplemental Cash Flow

Leases - Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows for operating leases	$ (3,050)	$ (1,901)

Leases - Operating Lease Right-

Leases - Operating Lease Right-of-use Assets and Liabilities (Details) - USD ($) $ in Thousands	Sep. 30, 2021	Dec. 31, 2020
Operating leases
Operating lease right-of-use assets	$ 9,234	$ 10,310
Operating lease liabilities, current	3,583	3,153
Operating lease liabilities, non-current	6,303	7,891
Total operating lease liabilities	$ 9,886	$ 11,044

Commitments and Contingencies (

Commitments and Contingencies (Details) $ in Millions	Sep. 30, 2021USD ($)
Commitments and Contingencies Disclosure [Abstract]
Purchase commitment, outstanding inventory and other	$ 623.7
Letters of credit outstanding, amount	$ 10.5

Stockholders' Equity - Narrativ

Stockholders' Equity - Narrative (Details)	1 Months Ended
	Aug. 31, 2021USD ($)shares	Sep. 30, 2021shares	Jun. 14, 2021$ / sharesshares	Jun. 13, 2021$ / sharesshares	Dec. 31, 2020shares
Equity [Abstract]
Capital stock, shares authorized (in shares)			510,000,000	271,920,636
Capital stock, par value (in dollars per share) | $ / shares			$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)		500,000,000	500,000,000	156,276,750	156,277,000
Preferred stock, shares authorized (in shares)		10,000,000	10,000,000	115,643,886	0
Common stock, shares issued (in shares)		212,827,249	207,300,000		5,678,000
Common stock, shares outstanding (in shares)		212,827,249	207,348,000		5,678,000
Preferred stock, shares issued (in shares)		0	0		0
Preferred stock, shares outstanding (in shares)		0	0		0
Common stock exchange ratio			0.8925
Common stock repurchased for employee withholding tax liability (in shares)	64,304
Common stock repurchased for employee withholding tax liability | $	$ 634,037

Stockholders' Equity - Reserved

Stockholders' Equity - Reserved Shares (Details) - shares	Sep. 30, 2021	Jun. 14, 2021
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	76,746,000	22,532,619
2021 Employee Stock Purchase Plan
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	1,630,000
Warrants
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	24,862,000
Earnout Stock
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	18,009,000
2010 Equity Incentive Plan
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	21,654,000	22,500,000
2021 Equity Incentive Plan
Class of Stock [Line Items]
Common stock reserved for issuance (in shares)	10,591,000	10,400,000

Warrants - Narrative (Details)

Warrants - Narrative (Details) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021USD ($)day$ / sharesshares	Sep. 27, 2021$ / shares	Jun. 13, 2021USD ($)	Dec. 31, 2020USD ($)shares	Aug. 31, 2020USD ($)$ / shares
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share)	$ 11.50
Warrant liability | $	$ 56,133			$ 39,670
Redemption price (in dollars per share)		$ 0.10
Redemption ratio		0.255
Warrants outstanding (in shares) | shares	24,847,788			5,104,030
Warrant Redemption Scenario One
Class of Warrant or Right [Line Items]
Share price redemption trigger (in usd per share)	$ 18
Public warrants
Class of Warrant or Right [Line Items]
Warrant liability | $			$ 84,600
Warrants outstanding (in shares) | shares	13,874,994			0
Public warrants | Warrant Redemption Scenario One
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share)	$ 0.01
Share price redemption trigger (in usd per share)	$ 18
Redemption notice period	30 days
Share price threshold trading days | day	20
Share price threshold consecutive trading days	30 days
Redemption period	30 days
Public warrants | Warrant Redemption Scenario Two
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share)	$ 0.10
Share price redemption trigger (in usd per share)	$ 10
Redemption notice period	30 days
Share price threshold trading days | day	20
Share price threshold consecutive trading days	30 days
Share price (in dollars per share)	$ 18
Private placement warrants
Class of Warrant or Right [Line Items]
Warrant liability | $			$ 57,600
Percentage vote of holders required for amendment	65.00%
Warrants outstanding (in shares) | shares	7,550,000			0
Private placement warrants | Warrant Redemption Scenario Two
Class of Warrant or Right [Line Items]
Share price redemption trigger (in usd per share)	$ 10
Other warrants
Class of Warrant or Right [Line Items]
Warrants outstanding (in shares) | shares	3,422,794			5,104,030
Convertible note warrants
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share)					$ 0.02
Warrant liability | $					$ 29,000
Warrants outstanding (in shares) | shares	3,421,902

Warrants - Activity (Details)

Warrants - Activity (Details)	9 Months Ended
	Sep. 30, 2021shares
Class of Warrant or Right [Line Items]
Outstanding (in shares)	5,104,030
Issued as part of the Merger (in shares)	21,424,994
Exercised (in shares)	(1,681,236)
Outstanding (in shares)	24,847,788
Number of shares issued during period resulting from conversion (in shares)	1,564,958
Public warrants
Class of Warrant or Right [Line Items]
Outstanding (in shares)	0
Issued as part of the Merger (in shares)	13,874,994
Exercised (in shares)	0
Outstanding (in shares)	13,874,994
Private placement warrants
Class of Warrant or Right [Line Items]
Outstanding (in shares)	0
Issued as part of the Merger (in shares)	7,550,000
Exercised (in shares)	0
Outstanding (in shares)	7,550,000
Other warrants
Class of Warrant or Right [Line Items]
Outstanding (in shares)	5,104,030
Issued as part of the Merger (in shares)	0
Exercised (in shares)	(1,681,236)
Outstanding (in shares)	3,422,794

Equity Plans and Stock-based _3

Equity Plans and Stock-based Compensation - Narrative (Details) - USD ($) $ / shares in Units, $ in Thousands	Jun. 14, 2021	Jun. 30, 2021	Mar. 31, 2020	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable, Number of options (in shares)				12,592,271		12,592,271
Awards granted (in shares)						674,643
Awards outstanding (in shares)				18,663,431		18,663,431		20,178,784
Stock-based compensation expense				$ 3,178	$ 2,680	$ 11,265	$ 7,551
Total intrinsic value of stock options exercised						10,300
Total estimated grant date fair value of stock options vested						10,200
Unrecognized stock-based compensation expense, stock options				$ 27,300		$ 27,300
2010 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Options exercisable, Number of options (in shares)	22,532,619			21,653,662		21,653,662
Common stock reserved for the Plan (in shares)				387,513		387,513
2021 Plan
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for the Plan (in shares)				10,000,000		10,000,000
Annual percentage increase in shares reserved						4.00%
Exercise price, percent of fair market value for greater than ten percent shareholders						110.00%
Number of shares that may be issued (in shares)						30,000,000
ESPP
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Common stock reserved for the Plan (in shares)				1,630,000		1,630,000
Annual percentage increase in shares reserved						1.00%
Number of shares that may be issued (in shares)						16,300,000
Stock options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period						10 years
Award vesting period						4 years
Unrecognized stock-based compensation expense, period for recognition						2 years 6 months
Stock options | Greater than 10% stockholder
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award expiration period						5 years
Restricted stock units (RSUs)
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period						4 years
Unrecognized stock-based compensation expense, period for recognition						3 years 7 months 6 days
Unrecognized stock-based compensation expense, RSUs				$ 9,300		$ 9,300
CEO Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Awards granted (in shares)			4,685,624
CEO Time-Based Awards at $4.75
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			4 years
Awards granted (in shares)			1,338,749
Award exercise price (in dollars per share)			$ 5.33
CEO Time-Based Awards at $10 to $25
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award vesting period			4 years
Awards outstanding (in shares)			2,677,500	2,677,500		2,677,500		2,677,500
CEO Time-Based Awards at $10 to $25 | Tranche One
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award exercise price (in dollars per share)			$ 11.21
CEO Time-Based Awards at $10 to $25 | Tranche Two
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award exercise price (in dollars per share)			16.81
CEO Time-Based Awards at $10 to $25 | Tranche Three
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award exercise price (in dollars per share)			22.41
CEO Time-Based Awards at $10 to $25 | Tranche Four
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award exercise price (in dollars per share)			28.02
Milestone Options
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Award exercise price (in dollars per share)			$ 5.33
Awards outstanding (in shares)			669,375					669,375
Number of shares that fully vested (in shares)	669,375
Stock-based compensation expense		$ 2,100

Equity Plans and Stock-based _4

Equity Plans and Stock-based Compensation - Outstanding Option Activity (Details) - USD ($) $ / shares in Units, $ in Thousands	1 Months Ended	9 Months Ended	12 Months Ended
	Mar. 31, 2020	Sep. 30, 2021	Dec. 31, 2020
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance at beginning of period (in shares)		20,178,784
Granted (in shares)		674,643
Exercised (in shares)		(1,676,533)
Cancelled/forfeited/expired (in shares)		(513,463)
Balance at end of period (in shares)		18,663,431	20,178,784
Options exercisable, Number of options (in shares)		12,592,271
Stock Options Weighted Average Exercise Price
Balance at beginning of period (in dollars per share)		$ 3.81
Granted (in dollars per share)		9.86
Exercised (in dollars per share)		3.24
Cancelled/forfeited/expired (in dollars per share)		5.09
Balance at end of period (in dollars per share)		4.04	$ 3.81
Options exercisable, Weighted average exercise price per share (in dollars per share)		$ 3.35
Stock Option Activity, Additional Disclosures
Options outstanding, Weighted average remaining contractual term		6 years 10 months 24 days	7 years 4 months 24 days
Options exercisable, Weighted average remaining contractual term		6 years
Options outstanding, Aggregate intrinsic value		$ 113,302	$ 65,056
Options exercisable, Aggregate intrinsic value		$ 85,124
CEO Time-Based Awards at $10 to $25
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance at beginning of period (in shares)		2,677,500
Balance at end of period (in shares)	2,677,500	2,677,500	2,677,500
Milestone Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance at beginning of period (in shares)		669,375
Balance at end of period (in shares)	669,375		669,375
CEO Equity Awards and Milestone Options
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Options exercisable, Number of options (in shares)		669,375	502,031
Equity Awards
Share-based Compensation Arrangement by Share-based Payment Award, Options, Outstanding [Roll Forward]
Balance at end of period (in shares)		1,004,064
Stock Options Weighted Average Exercise Price
Options exercisable, Weighted average exercise price per share (in dollars per share)		$ 19.61

Equity Plans and Stock-based _5

Equity Plans and Stock-based Compensation - Assumptions Used in Fair Value Measurement (Details) - Stock options	9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020
Share-based Compensation Arrangement by Share-based Payment Award [Line Items]
Expected term	6 years 2 months 12 days	6 years
Risk-free interest rate	1.00%	0.50%
Expected volatility	53.90%	73.10%
Expected dividend rate	0.00%	0.00%

Equity Plans and Stock-based _6

Equity Plans and Stock-based Compensation - Stock-based Compensation Expense (Details) - USD ($) $ in Thousands	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 3,178	$ 2,680	$ 11,265	$ 7,551
Cost of goods sold
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	319	235	865	688
Research and development
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	567	461	1,625	1,183
Selling, general and administrative
Share-based Payment Arrangement, Expensed and Capitalized, Amount [Line Items]
Stock-based compensation expense	$ 2,292	$ 1,984	$ 8,775	$ 5,680

Equity Plans and Stock-based _7

Equity Plans and Stock-based Compensation - RSU Activity (Details) - Restricted stock units (RSUs) - USD ($) $ / shares in Units, $ in Thousands	9 Months Ended
	Sep. 30, 2021	Dec. 31, 2020
Number of RSUs
Balance (in shares)	0
Granted (in shares)	857,199
Vested (in shares)	0
Cancelled/forfeited (in shares)	(9,441)
Balance (in shares)	847,758
Weighted Average Grant Date Fair Value
Balance (in dollars per share)	$ 0
Granted (in dollars per share)	11.33
Vested (in dollars per share)	0
Cancelled/forfeited (in dollars per share)	11.33
Balance (in dollars per share)	$ 11.33
Aggregate intrinsic value	$ 8,571	$ 0

Net Income (Loss) Per Share - C

Net Income (Loss) Per Share - Calculation (Details) $ / shares in Units, shares in Thousands, $ in Thousands	Jun. 14, 2021USD ($)	Sep. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares	Jun. 30, 2021USD ($)	Sep. 30, 2021USD ($)$ / sharesshares	Sep. 30, 2020USD ($)$ / sharesshares
Numerator:
Net income (loss)		$ 36,321	$ (46,860)		$ (204,868)	$ (94,384)
Gain on valuation of warrant liabilities		(73,197)	0		0	0
Interest expense to be recognized upon conversion of Convertible Notes		(61,774)	0		0	0
Numerator for diluted EPS - Net loss after the effect of dilutive securities		$ (98,650)	$ (46,860)		$ (204,868)	$ (94,384)
Denominator:
Basic weighted average shares (in shares) | shares		212,071	4,406		89,233	4,139
Dilutive impact of public and private placement warrants (in shares) | shares		594	0		0	0
Convertible Notes (in shares) | shares		24,300	0		0	0
Diluted weighted average shares (in shares) | shares		236,965	4,406		89,233	4,139
Net income (loss) per share of common stock:
Basic (in dollars per share) | $ / shares		$ 0.17	$ (10.64)		$ (2.30)	$ (22.80)
Diluted (in dollars per share) | $ / shares		(0.42)	$ (10.64)		(2.30)	$ (22.80)
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share) | $ / shares		$ 11.50			11.50
Common stock exchange ratio	0.8925
Convertible Notes
Class of Warrant or Right [Line Items]
Write off of unamortized debt discount	$ 21,000			$ 68,800
Interest expense		$ 7,000
Convertible note warrants, $0.02 per share
Class of Warrant or Right [Line Items]
Exercise price of warrants (in dollars per share) | $ / shares		$ 0.02			$ 0.02

Net Income (Loss) Per Share - N

Net Income (Loss) Per Share - Narrative (Details)	Jun. 14, 2021
Earnings Per Share [Abstract]
Common stock exchange ratio	0.8925

Net Income (Loss) Per Share - P

Net Income (Loss) Per Share - Potentially Dilutive Securities (Details) shares in Thousands	3 Months Ended
	Sep. 30, 2021shares
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities (in shares)	22,859
Stock options and RSUs
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities (in shares)	22,858
Other warrants
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Potentially dilutive securities (in shares)	1

401(k) Plan (Details)

401(k) Plan (Details) - USD ($) $ in Millions	3 Months Ended		9 Months Ended
	Sep. 30, 2021	Sep. 30, 2020	Sep. 30, 2021	Sep. 30, 2020
Retirement Benefits [Abstract]
Employer matching contribution, percent of match			4.00%
Employer matching contribution, cost	$ 0.6	$ 0.5	$ 1.8	$ 1.4

Subsequent Events (Details)

Subsequent Events (Details) - USD ($)	1 Months Ended	9 Months Ended
	Oct. 31, 2021	Sep. 30, 2021
Subsequent Event [Line Items]
Warrants exercised (in shares)		1,681,236
Issuance of common stock upon exercise of warrant (in shares)		1,564,958
Public warrants
Subsequent Event [Line Items]
Warrants exercised (in shares)		0
Private placement warrants
Subsequent Event [Line Items]
Warrants exercised (in shares)		0
Subsequent event
Subsequent Event [Line Items]
Gain on change in fair value of warrants	$ 2,700,000
Reclassification of warrant liability to equity	$ 53,400,000
Subsequent event | Exercised for cash
Subsequent Event [Line Items]
Issuance of common stock upon exercise of warrant (in shares)	10,599
Proceeds from exercise of warrants	$ 121,889
Subsequent event | Cashless exercise
Subsequent Event [Line Items]
Issuance of common stock upon exercise of warrant (in shares)	5,351,231
Subsequent event | Public warrants
Subsequent Event [Line Items]
Warrants redeemed (in shares)	428,145
Proceeds from redemption of warrants	$ 42,815
Subsequent event | Public warrants | Exercised for cash
Subsequent Event [Line Items]
Warrants exercised (in shares)	10,599
Subsequent event | Public warrants | Cashless exercise
Subsequent Event [Line Items]
Warrants exercised (in shares)	13,436,250
Subsequent event | Private placement warrants | Cashless exercise
Subsequent Event [Line Items]
Warrants exercised (in shares)	7,550,000