Hyliion (HYLN) 10-K 25 Feb 25 2024 FY Annual report Financial data

Cover

Cover - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Feb. 20, 2025	Jun. 30, 2024
Cover [Abstract]
Document Type	10-K
Document Annual Report	true
Current Fiscal Year End Date	--12-31
Document Period End Date	Dec. 31, 2024
Document Transition Report	false
Entity File Number	001-38823
Entity Registrant Name	HYLIION HOLDINGS CORP.
Entity Incorporation, State or Country Code	DE
Entity Tax Identification Number	83-2538002
Entity Address, Address Line One	1202 BMC Drive
Entity Address, Address Line Two	Suite 100
Entity Address, City or Town	Cedar Park
Entity Address, State or Province	TX
Entity Address, Postal Zip Code	78613
City Area Code	833
Local Phone Number	495-4466
Title of 12(b) Security	Common Stock
Trading Symbol	HYLN
Security Exchange Name	NYSEAMER
Entity Well-known Seasoned Issuer	No
Entity Voluntary Filers	No
Entity Current Reporting Status	Yes
Entity Interactive Data Current	Yes
Entity Filer Category	Non-accelerated Filer
Entity Small Business	true
Entity Emerging Growth Company	false
ICFR Auditor Attestation Flag	false
Document Financial Statement Error Correction	false
Entity Shell Company	false
Entity Public Float			$ 224
Entity Common Stock, Shares Outstanding		174,820,174
Documents Incorporated by Reference	Portions of the registrant’s definitive proxy statement for the 2025 Annual Meeting of Stockholders, to be filed no later than 120 days after the end of the fiscal year to which this Annual Report on Form 10-K relates, are incorporated by reference into Part III of this Annual Report on Form 10-K.
Amendment Flag	false
Entity Central Index Key	0001759631
Document Fiscal Year Focus	2024
Document Fiscal Period Focus	FY

Audit Information

Audit Information	12 Months Ended
	Dec. 31, 2024
Audit Information [Abstract]
Auditor Firm ID	248
Auditor Name	GRANT THORNTON LLP
Auditor Location	Dallas, Texas

CONSOLIDATED BALANCE SHEETS

CONSOLIDATED BALANCE SHEETS - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Current assets
Cash and cash equivalents	$ 9,227	$ 12,881
Accounts receivable, net	1,923	40
Prepaid expenses and other current assets	6,401	18,483
Short-term investments	110,918	150,297
Assets held for sale	2,563	0
Total current assets	131,032	181,701
Property and equipment, net	25,920	9,987
Operating lease right-of-use assets	5,431	7,070
Other assets	1,079	1,439
Long-term investments	99,584	128,186
Total assets	263,046	328,383
Current liabilities
Accounts payable	5,243	4,224
Current portion of operating lease liabilities	2,426	847
Accrued expenses and other current liabilities	6,622	10,051
Total current liabilities	14,291	15,122
Operating lease liabilities, net of current portion	4,366	6,792
Other liabilities	0	203
Total liabilities	18,657	22,117
Commitments and contingencies (Note 12)
Stockholders’ equity
Common stock, $0.0001 par value; 250,000,000 shares authorized; 184,428,472 and 183,071,317 shares issued as of December 31, 2024 and 2023, respectively; 173,818,402 and 183,034,255 shares outstanding as of December 31, 2024 and 2023, respectively	18	18
Additional paid-in capital	408,315	404,045
Treasury stock, at cost; 10,610,070 and 37,062 shares as of December 31, 2024 and 2023, respectively	(14,132)	(33)
Accumulated deficit	(149,812)	(97,764)
Total stockholders’ equity	244,389	306,266
Total liabilities and stockholders’ equity	$ 263,046	$ 328,383

CONSOLIDATED BALANCE SHEETS (Pa

CONSOLIDATED BALANCE SHEETS (Parentheticals) - $ / shares	Dec. 31, 2024	Dec. 31, 2023
Statement of Financial Position [Abstract]
Common stock, par value (in dollars per share)	$ 0.0001	$ 0.0001
Common stock, shares authorized (in shares)	250,000,000	250,000,000
Common stock, shares issued (in shares)	184,428,472	183,071,317
Common stock, shares outstanding (in shares)	173,818,402	183,034,255
Treasury stock (in shares)	10,610,070	37,062

CONSOLIDATED STATEMENTS OF OPER

CONSOLIDATED STATEMENTS OF OPERATIONS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Revenues
Revenues	$ 1,509	$ 672
Cost of revenues
Cost of revenues	1,415	1,716
Gross profit (loss)	94	(1,044)
Operating expenses
Research and development	37,004	82,240
Selling, general and administrative	24,382	42,611
Exit and termination costs	3,007	11,474
Total operating expenses	64,393	136,325
Loss from operations	(64,299)	(137,369)
Interest income	12,216	13,808
Gain on disposal of assets	3	1
Other income, net	32	50
Net loss	$ (52,048)	$ (123,510)
Net loss per share, basic (in dollars per share)	$ (0.30)	$ (0.68)
Net loss per share, diluted (in dollars per share)	$ (0.30)	$ (0.68)
Weighted-average shares outstanding, basic (in shares)	174,915,487	181,411,069
Weighted-average shares outstanding, diluted (in shares)	174,915,487	181,411,069
Product sales and other
Revenues
Revenues	$ 0	$ 672
Cost of revenues
Cost of revenues	0	1,716
Research and development services
Revenues
Revenues	1,509	0
Cost of revenues
Cost of revenues	$ 1,415	$ 0

CONSOLIDATED STATEMENTS OF CHAN

CONSOLIDATED STATEMENTS OF CHANGES IN STOCKHOLDERS’ EQUITY - USD ($) $ in Thousands	Total	Common Stock	Treasury Stock	Additional Paid-In Capital	(Accumulated Deficit) Retained Earnings
Balance at beginning (in Shares) at Dec. 31, 2022		179,826,309
Balance at beginning at Dec. 31, 2022	$ 423,574	$ 18	$ 0	$ 397,810	$ 25,746
Balance at beginning of treasury stock (in shares) at Dec. 31, 2022			0
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options and vesting of restricted stock units, net (in shares)		3,245,008
Exercise of common stock options and vesting of restricted stock units, net	18			18
Share-based compensation	6,217			6,217
Repurchase of treasury stock (in shares)			(37,062)
Repurchase of treasury stock	(33)		$ (33)
Net loss	$ (123,510)				(123,510)
Balance at ending (in Shares) at Dec. 31, 2023	183,034,255	183,071,317
Balance at ending at Dec. 31, 2023	$ 306,266	$ 18	$ (33)	404,045	(97,764)
Balance at ending of treasury stock (in shares) at Dec. 31, 2023	(37,062)		(37,062)
Increase (Decrease) in Stockholders' Equity [Roll Forward]
Exercise of common stock options and vesting of restricted stock units, net (in shares)		1,357,155
Exercise of common stock options and vesting of restricted stock units, net	$ (345)			(345)
Share-based compensation	4,615			4,615
Repurchase of treasury stock (in shares)			(10,573,008)
Repurchase of treasury stock	(14,099)		$ (14,099)
Net loss	$ (52,048)				(52,048)
Balance at ending (in Shares) at Dec. 31, 2024	173,818,402	184,428,472
Balance at ending at Dec. 31, 2024	$ 244,389	$ 18	$ (14,132)	$ 408,315	$ (149,812)
Balance at ending of treasury stock (in shares) at Dec. 31, 2024	(10,610,070)		(10,610,070)

CONSOLIDATED STATEMENTS OF CASH

CONSOLIDATED STATEMENTS OF CASH FLOWS - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Cash flows from operating activities
Net loss	$ (52,048)	$ (123,510)
Adjustments to reconcile net loss to net cash used in operating activities:
Depreciation and amortization	3,147	3,511
Amortization and accretion of investments, net	(3,078)	(2,868)
Noncash lease expense	1,639	1,496
Inventory write-down	0	1,139
Gain on disposal of assets, including assets held for sale	(2,850)	(1)
Share-based compensation	4,615	6,217
Carrying value adjustment to assets held for sale	6,464	0
Change in operating assets and liabilities:
Accounts receivable	(1,883)	1,096
Inventory	0	(1,065)
Prepaid expenses and other assets	(5,444)	463
Accounts payable	(2,865)	1,356
Accrued expenses and other liabilities	(3,588)	(3,020)
Operating lease liabilities	(847)	(1,776)
Net cash used in operating activities	(56,738)	(116,962)
Cash flows from investing activities
Purchase of property and equipment	(16,525)	(7,401)
Proceeds from sale of property and equipment	5,385	2
Payments for security deposit	0	(45)
Purchase of investments	(96,253)	(189,670)
Proceeds from sale and maturity of investments	166,886	215,422
Net cash provided by investing activities	59,493	18,308
Cash flows from financing activities
Proceeds from exercise of common stock options	67	257
Taxes paid related to net share settlement of equity awards	(412)	(239)
Repurchase of treasury stock	(13,982)	(33)
Net cash used in financing activities	(14,327)	(15)
Net decrease in cash and cash equivalents and restricted cash	(11,572)	(98,669)
Cash and cash equivalents and restricted cash, beginning of period	21,464	120,133
Cash and cash equivalents and restricted cash, end of period	$ 9,892	$ 21,464

Description of Organization and

Description of Organization and Business Operations and Basis of Presentation	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Description of Organization and Business Operations and Basis of Presentation	Note 1. Description of Organization and Business Operations and Basis of Presentation Overview Hyliion Holdings Corp. is a Delaware corporation headquartered in Cedar Park, Texas, that designs and develops power generators for stationary and mobile applications and provides research and development (“R&D”) services. References to the “Company,” “Hyliion,” “we,” or “us” in this report refer to Hyliion Holdings Corp. and its wholly owned subsidiary, unless expressly indicated or the context otherwise requires. The Company plans to develop and commercialize a fuel-agnostic generator (the “KARNO generator”) to be used in stationary power applications. The Company believes the KARNO generator is well positioned to address the rising strain on electrical infrastructure, notably from electric vehicles. Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements include the accounts of Hyliion Holdings Corp. and its wholly owned subsidiary. Intercompany transactions and balances have been eliminated upon consolidation. The consolidated financial statements and accompanying notes have been prepared in a ccordance with accounting principles generally accepted in the United States of America (“GAAP”) and in accordance with the rules and regulations of the Unites States Securities and Exchange Commission (“SEC”). Any reference in these footnotes to the applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”). These consolidated financial statements have been prepared on a going concern basis, which contemplates the realization of assets and settlement of liabilities in the normal course of business. The Company is an early-stage growth company and has generated negative cash flows from operating activities since inception. At December 31, 2024, the Company had total equity of $244.4 million, inclusive of cash and cash equivalents of $9.2 million and total investments of $210.5 million. Based on this, the Company has sufficient funds to continue to execute its business strategy for the next twelve months from the issuance date of the financial statements included in this Annual Report on Form 10-K.

Disposals

Disposals	12 Months Ended
	Dec. 31, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Disposals	Note 2. Disposals On November 7, 2023, the Board of the Company approved a strategic plan to wind down its powertrain business and preserve the related intellectual property (the “Plan”). As part of the Plan, the Company will continue to focus on commercialization of its KARNO generator technology. We have not accounted for the impacts of the Plan as a discontinued operation through December 31, 2024 as we have not abandoned or sold the underlying intellectual property and continue wind down activities. We expect to complete wind down activities in the fourth quarter of fiscal year 2025. Total charges and expenses related to the Plan of $3.0 million and $11.5 million for the years ended December 31, 2024 and 2023, respectively , inclusive of recoveries from assets sold and charges to assets held for sale discussed below, are included in exit and termination costs Note 10 , and accounts payable, and is summarized as follows (in millions): December 31, 2023 Charged to Expense (Benefit) Costs Paid or Settled December 31, 2024 Employee severance and retention $ 1.1 $ — $ (1.0) $ 0.1 Contract terminations 6.5 (0.8) (5.1) 0.6 Warranty obligations 0.4 (0.3) — 0.1 $ 8.0 $ (1.1) $ (6.1) $ 0.8 December 31, 2022 Charged to Expense Costs Paid or Settled December 31, 2023 Employee severance and retention $ — $ 1.2 $ (0.1) $ 1.1 Contract terminations — 8.2 (1.7) 6.5 Warranty obligations 0.5 0.1 (0.2) 0.4 $ 0.5 $ 9.5 $ (2.0) $ 8.0 The above estimates of the cash expenditures and charges that the Company expects to incur in connection with the Plan, and the timing thereof, are subject to a number of assumptions and actual amounts may differ materially from estimates. In addition, the Company may incur other cash expenditures or charges not currently contemplated due to unanticipated events. Assets Held for Sale Through the quarter ended December 31, 2024, certain assets of our powertrain business, including Class 8 semi-trucks and capital equipment, were being actively marketed for sale, and we were actively locating buyers for these assets at prices that were reasonable in relation to their current fair value and the assets were available for immediate sale in their present condition. At the time of initial classification as held for sale, we estimated that the sale of these assets was expected to be completed within one year and it was unlikely that significant changes to the plan of sale would be made. We review assets held for sale each reporting period to determine whether the existing carrying amounts are fully recoverable in comparison to their estimated fair values less costs to sell. We had assets held for sale of $2.6 million and nil consisting of property and equipment in connection with the Plan at their fair value less costs to sell at December 31, 2024 and 2023, respectively. We used fair value hierarchy Level III inputs including comparable assets, adjusted for condition, and recorded charges of $6.5 million and nil included in exit and termination costs in the consolidated statements of operations f or the years ended December 31, 2024 and 2023, respectively. The estimates of fair value less costs to sell are subject to a number of assumptions and actual amoun ts may differ materially from estimates. We recorded net benefits for recoveries related to asset sales of $2.8 million and nil included in exit and termination costs in the consolidated statements of operations f or the years ended December 31, 2024 and 2023, respectively and included in gain on disposal of assets in the consolidated statements of cash flows for the years ended December 31, 2024 and 2023, respectively.

Summary of Significant Accounti

Summary of Significant Accounting Policies	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Summary of Significant Accounting Policies	Note 3. Summary of Significant Accounting Policies Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the balance sheet date, as well as reported amounts of expenses during the reporting period. The Company’s most significant estimates and judgments involve revenue, assets held for sale, income taxes and valuation of share-based compensation. Management bases its estimates on historical experience and on various other assumptions believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results could differ from those estimates, and such differences could be material to the Company’s consolidated financial statements. Segment Information ASC 280, Segment Reporting , defines operating segments as components of an enterprise where discrete financial information is available that is evaluated regularly by the chief operating decision-maker (“CODM”) in deciding how to allocate resources and in assessing performance. The Company operates as a single operating segment from which all revenue and net income (loss) is derived and for which all assets are attributed. The Company’s CODM is the chief executive officer, who has ultimate responsibility for the operating performance of the Company and the allocation of resources. The CODM uses net income (loss) to manage the business and does not segment the business for internal reporting or decision making. The significant expense categories and amounts that are regularly provided to the CODM and included in the reported measure of segment loss for the years ended December 31, 2024 and 2023 are summarized as follows (in millions): Year Ended December 31, 2024 2023 Total revenues $ 1.5 $ 0.7 Total cost of revenues 1.4 1.7 Gross profit (loss) 0.1 (1.0) Administrative and office 7.7 12.4 Depreciation and amortization 3.1 2.4 Facilities 5.1 5.0 Personnel 24.3 46.7 Product development, exclusive of other costs presented 15.0 34.0 Professional services 5.2 21.7 Exit and termination costs 3.0 11.5 Other operating expense 1.0 2.6 Total operating expenses 64.4 136.3 Other income, net 12.3 13.8 Net loss $ (52.0) $ (123.5) Concentration of Supplier Risk The Company is dependent on certain suppliers, the majority of which are single source suppliers, and the inability of these suppliers to deliver necessary components of the Company’s products in a timely manner at prices, quality levels and volumes that are acceptable, or the Company’s inability to efficiently manage these components from these suppliers, could have a material adverse effect on the Company’s business, prospects, financial condition and operating results. Cash and Cash Equivalents The Company considers all highly liquid investments with a maturity date of 90 days or less at the time of purchase to be cash and cash equivalents only if in checking, savings or money market accounts. Cash and cash equivalents include cash held in banks and money market accounts and are carried at cost, which approximates fair value. The Company maintains cash in excess of federally insured limits at financial institutions which it believes are of high credit quality and has not incurred any losses related to these balances to date. The Company believes its credit risk, with respect to these financial institutions to be minimal. Restricted Cash The Company provided a supplier with a letter of credit for $7.9 million in the fourth quarter of 2023 to secure the performance of the Company, backed by a restricted cash deposit to pay any draws on the letter of credit by the supplier. The Company was released from this letter of credit in the first quarter of 2024. The Company has provided its corporate headquarters lessor with a letter of credit for $0.7 million to secure the performance of the Company’s lease obligations, backed by a restricted cash deposit to pay any draws on the letter of credit by the lessor. Total cash and cash equivalents and restricted cash as presented in the consolidated statements of cash flows is summarized as follows: December 31, 2024 December 31, 2023 December 31, 2022 Cash and cash equivalents $ 9,227 $ 12,881 $ 119,468 Restricted cash included in prepaid expenses and other current assets — 7,918 — Restricted cash included in other assets 665 665 665 $ 9,892 $ 21,464 $ 120,133 Accounts Receivable Accounts receivable are stated at a gross invoice amount, net of an allowance for doubtful accounts. The allowance for doubtful accounts is maintained at a level considered adequate to provide for potential account losses on the balance based on the Company’s evaluation of the anticipated impact of current economic conditions, changes in the character and size of the balance, past and expected future loss experience and other pertinent factors. At December 31, 2024 and 2023, accounts receivable included amounts receivable from customers of $1.5 million and nil, respectively. At December 31, 2024 and 2023 there was no allowance for doubtful accounts on customer receivables. Investments The Company’s investments consist of corporate bonds, U.S. treasury and agency securities, state and local municipal bonds and commercial paper, all of which are classified as held-to-maturity, with a maturity date of 36-months or less at the time of purchase. The Company determines the appropriate classification of investments at the time of purchase and re-evaluates such designation as of each balance sheet date. Investments are classified as held-to-maturity when the Company has the positive intent and ability to hold the securities to maturity. Held-to-maturity securities are stated at amortized cost, adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization, along with interest, is included in interest income. The Company uses the specific identification method to determine the cost basis of securities sold. Investments are impaired when a decline in fair value is judged to be other-than-temporary. The Company evaluates investments for impairment by considering the length of time and extent to which market value has been less than cost or amortized cost, the financial condition and near-term prospects of the issuer as well as specific events or circumstances that may influence the operations of the issuer and the Company’s intent to sell the security or the likelihood that it will be required to sell the security before recovery of the entire amortized cost. Once a decline in fair value is determined to be other-than-temporary, an impairment charge is recorded to other income (expense) and a new cost basis in the investment is established. Fair Value Measurements ASC 820, Fair Value Measurements , clarifies that fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based upon assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, ASC 820 establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level I : Quoted prices (unadjusted) for identical assets or liabilities in active markets that the Company can access at the measurement date; Level II : Significant other observable inputs other than level I prices such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data; and Level III : Significant unobservable inputs that reflect the Company’s own assumptions about the assumptions that market participants would use in pricing an asset or liability. An asset’s or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques used need to maximize the use of observable inputs and minimize the use of unobservable inputs. The Company believes its valuation methods are appropriate and consistent with other market participants, however the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. The Company’s financial instruments consist of cash and cash equivalents and restricted cash, accounts receivable, investments, accounts payable and accrued expenses. The carrying value of cash and cash equivalents and restricted cash, accounts receivable, accounts payable and accrued expenses approximate fair value because of the short-term nature of those instruments. The fair value of investments is based on quoted prices for identical or similar instruments in markets that are not active. As a result, investments are classified within Level II of the fair value hierarchy. Inventories Through December 31, 2024, we have not yet commercialized the KARNO generator. Costs incurred for components acquired prior to our determination of reaching a commercial stage are expensed as R&D costs, resulting in zero cost basis for those components. As a result, moving-average prices for inventory that is capitalized in future periods may be significantly affected by those zero cost items. Inventory is consumed in the performance of contracts for R&D services in the quarter in which it is purchased, including certain allocations of overhead costs, and we therefore do not record inventory at each reporting period pertaining to these contracts. Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets include prepaid insurance, rent and supplies, which are expected to be recognized, received or realized within the next 12 months. Property and Equipment, Net Property and equipment, net is stated at cost less accumulated depreciation, or if acquired in a business combination, at allocated fair value at the date of acquisition. Depreciation is calculated using the straight-line method, based upon the following estimated useful lives: Production machinery and equipment 2 to 12 years Vehicles 3 to 7 years Leasehold improvements shorter of lease term or 7 years Furniture and fixtures 3 years Computers and related equipment 3 to 7 years Major renewals and improvements are capitalized, while replacements, maintenance and repairs, which do not improve or extend the lives of the respective assets, are expensed as incurred. When property and equipment is retired or otherwise disposed of, the related cost and accumulated depreciation are removed from the accounts, and any gain or loss on the disposition is recorded in the consolidated statement of operations as a component of other income (expense). All long-lived assets are located in the U.S. Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment and intangible assets with definite lives, for impairment whenever events or changes in circumstances indicate that an asset group’s carrying amount may not be recoverable. The Company conducts its long-lived asset impairment analysis in accordance with ASC 360-10, Impairment or Disposal of Long-Lived Assets , which requires the Company to group assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and evaluate the asset group against the sum of the undiscounted future cash flows. If the undiscounted cash flows do not indicate the carrying amount of the asset group is recoverable, an impairment charge is measured as the amount by which the carrying amount of the asset group exceeds its fair value. Revenue The Company follows five steps to recognize revenue from contracts with customers under ASC 606, Revenue from Contracts with Customers, which are: • Step 1: Identify the contract(s) with a customer; • Step 2: Identify the performance obligations in the contract; • Step 3: Determine the transaction price; • Step 4: Allocate the transaction price to the performance obligations in the contract; and • Step 5: Recognize revenue when (or as) a performance obligation is satisfied. Product Sales The Company has historically generated revenues from sales of hybrid systems for Class 8 semi-trucks and limited quantities of Class 8 semi-trucks outfitted with the hybrid system. We recognized revenue on Hybrid system sales and Class 8 semi-trucks outfitted with Hybrid systems upon delivery to, and acceptance of the vehicle by, the customer, which is when control transferred. Contracts were reviewed for significant financing components and payments were typically received within 30 days of delivery. The sale of a Hybrid system to an end-use fleet customer consisted of a completed modification to the customer vehicle and the installation services involved significant integration of the Hybrid system with the customer’s vehicle. Installation services were not distinct within the context of the contract and together with the sale of the Hybrid system represented a single performance obligation. We did not offer any sales returns. Amounts billed to customers related to shipping and handling were classified as revenue, and we elected to recognize the cost for freight and shipping when control transferred to the customer as a cost of revenue. Our policy was to exclude taxes collected from customers from the transaction price of contracts. The Company has discontinued the electrified powertrain systems business and shifted to focus on the development and commercialization of the fuel-agnostic KARNO generator technology. U.S. Government Contracts The Company was performing under two contracts as both a prime and subcontractor to the United States government to provide R&D services. The larger of these two contracts was modified and accounted for as a new contract in the quarter ending December 31, 2024. These contracts were not accounted for as revenue prior to September 30, 2024 as they were not in the ordinary course of business and the counterparties were not customers under GAAP. In September 2024, the Company was awarded a best effort cost-plus-fixed fee contract up to $16.0 million by the United States Department of the Navy’s Office of Naval Research (“ONR”) to research the suitability of its KARNO generator for Navy ships and stationary power applications. Under the agreement, the Company will provide R&D services through September 2026, including delivery of up to seven KARNO generators. The ONR contract represented a significant change in business strategy toward providing R&D activities in the ordinary course of business in addition to developing power generators for stationary and mobile applications. The Company now accounts for all three contracts under ASC 606 beginning in the quarter ending December 31, 2024. The remaining amounts of revenue that we may recognize under these contracts was up to $15.7 million as of December 31, 2024, which is expected to be recognized in 2025 and 2026. There is a single research and development services performance obligation in each of these contracts that is measured over time as the services are performed. The Company generally invoices monthly which corresponds directly with the value to the customers of the performance completed to date, and recognizes revenue in the amount that it has a right to invoice. Payment is ordinarily due within 90 days of invoice submission. Cost of R&D services revenue includes labor, allocated fringe and overhead, and inventory. All revenue in the year ended December 31, 2024 was recognized over time and all revenue in the year ended December 31, 2023 was recognized at a point in time. The portion of our revenues from significant customers is summarized as follows and is attributable to the U.S.: Year Ended December 31, 2024 2023 Customer A 88 % — % Customer B 12 — Customer C — 65 Customer D — 25 100 % 90 % Leases We determine if an arrangement is a lease at inception of the contract. Operating leases are included in operating lease right-of-use (“ROU”) assets, current portion of operating lease liabilities, and operating lease liabilities, net of current portion in the accompanying consolidated balance sheets. We have lease agreements with lease and non-lease components, and have elected to utilize the practical expedient to account for lease and non-lease components together as a single combined lease component. Variable lease costs consist primarily of common area maintenance. ROU assets represent the Company’s right to use underlying assets for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the leases. ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The discount rate used to calculate the present value for lease payments is the Company’s incremental borrowing rate, which is determined based on information available at lease commencement and is equal to the rate of interest that the Company would have to pay to borrow on a collateralized basis over a similar term in an amount equal to the lease payments in a similar economic environment. The Company uses the implicit rate when readily determinable. The Company’s real estate leases may include one or more options to renew, with the renewal extending the lease term for an additional one Marketing, Promotional and Advertising Costs Marketing, promotional and advertising costs are expensed as incurred and are included as an element of selling, general and administrative expense in the consolidated statement of operations. Marketing, promotional and advertising costs were $0.1 million and $1.3 million for the years ended December 31, 2024 and 2023, respectively. Research and Development Expense R&D costs did not meet the requirements to be recognized as an asset as the associated future benefits were at best uncertain and there was no alternative future use at the time the costs were incurred. R&D costs include, but are not limited to, outsourced engineering services, allocated facilities costs, depreciation on equipment utilized in R&D activities, internal engineering and development expenses, materials, internally-developed software and employee related expenses (including salaries, benefits, travel, and share-based compensation) related to development of the Company’s products and services. Share-Based Compensation The Company accounts for share-based compensation in accordance with ASC 718, Compensation – Stock Compensation , under which shared based payments that involve the issuance of common stock to employees and nonemployees and meet the criteria for equity-classified awards are recognized in the financial statements as share-based compensation expense based on the fair value on the date of grant. The Company issues restricted stock awards to employees and nonemployees, utilizing new shares. The Company has elected to recognize the adjustment to share-based compensation expense in the period in which forfeitures occur. We recognize compensation expense for awards with only service conditions on a straight-line basis over the requisite service period for the entire award. If factors change, and we utilize different assumptions including the probability of achieving performance conditions, share-based compensation cost on future award grants may differ significantly from share-based compensation cost recognized on past award grants. If there are any modifications or cancellations of the underlying unvested securities, we may be required to accelerate any remaining unearned share-based compensation cost or incur incremental cost. Share-based compensation cost primarily affects our R&D and selling, general and administrative expenses. Income Taxes The Company accounts for income taxes in accordance with ASC 740, Income Taxes , under which deferred tax liabilities and assets are recognized for the expected future tax consequences of temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities and net operating loss and tax credit carryforwards. Valuation allowances are established when necessary to reduce deferred tax assets to the amount expected to be realized. Due to the Company’s history of losses since inception, the net deferred tax assets have been fully offset by a valuation allowance at December 31, 2024 and 2023. Uncertain tax positions taken or expected to be taken in a tax return are accounted for using the more likely than not threshold for financial statement recognition and measurement. For the years ended December 31, 2024 and 2023, there were no uncertain tax positions taken or expected to be taken in the Company’s tax returns. Net Loss Per Share Basic loss per share (“EPS”) is computed by dividing net loss (the numerator) by the weighted average number of common shares outstanding for the period (the denominator). Diluted EPS attributable to common shareholders is computed by adjusting net loss by the weighted average number of common shares and potential common shares outstanding (if dilutive) during each period. Potential common shares include shares issuable upon exercise of stock options and vesting of restricted stock awards (see Note 7). The number of potential common shares outstanding are calculated using the treasury stock or if-converted method. Recent Accounting Pronouncements In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40), and clarified by ASU 2025-01, to enable investors to better understand the major components of an entity’s income statement. The pronouncement is effective for fiscal years beginning after December 15, 2026 and interim periods beginning after December 15, 2027 and we expect a material impact to our disclosures as a result of adoption. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) , to enhance transparency and decision usefulness of income tax disclosures. The pronouncement is effective for fiscal years beginning after December 15, 2024 and we expect a material impact to our disclosures as a result of adoption. In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures , to improve the disclosures about a public entity’s reportable segments. The pronouncement is effective for fiscal years beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024. The Company adopted ASU 2023-07 for the year ended December 31, 2024 and updated its related disclosures.

Investments

Investments	12 Months Ended
	Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Investments	Note 4. Investments The amortized cost, unrealized gains and losses, and fair value, and maturities of our held-to-maturity investments at December 31, 2024 and 2023 are summarized as follows: Fair Value Measurements at December 31, 2024 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Commercial paper $ 979 $ 3 $ — $ 982 U.S. government agency bonds 17,490 6 (54) 17,442 State and municipal bonds 10,924 10 — 10,934 Corporate bonds and notes 181,109 369 (152) 181,326 $ 210,502 $ 388 $ (206) $ 210,684 Fair Value Measurements at December 31, 2023 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Commercial paper $ 35,218 $ 18 $ (10) $ 35,226 U.S. government agency bonds 27,602 56 (186) 27,472 State and municipal bonds 15,262 1 (48) 15,215 Corporate bonds and notes 200,401 515 (255) 200,661 $ 278,483 $ 590 $ (499) $ 278,574 December 31, 2024 December 31, 2023 Amortized Cost Fair Value Amortized Cost Fair Value Due in one year or less $ 110,918 $ 111,170 $ 150,297 $ 149,934 Due after one year through five years 99,584 99,514 128,186 128,640 $ 210,502 $ 210,684 $ 278,483 $ 278,574

Fair Value Measurements

Fair Value Measurements	12 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Fair Value Measurements	Note 5. Fair Value Measurements The fair value measurements of our financial assets at December 31, 2024 and 2023 are summarized as follows: Fair Value Measurements at December 31, 2024 Level I Level II Level III Total Cash and cash equivalents $ 9,227 $ — $ — $ 9,227 Restricted cash 665 — — 665 Held-to-maturity investments: Commercial paper — 982 — 982 U.S. government agency bonds — 17,442 — 17,442 State and municipal bonds — 10,934 — 10,934 Corporate bonds and notes — 181,326 — 181,326 $ 9,892 $ 210,684 $ — $ 220,576 Fair Value Measurements at December 31, 2023 Level I Level II Level III Total Cash and cash equivalents $ 12,881 $ — $ — $ 12,881 Restricted cash 8,583 — — 8,583 Held-to-maturity investments: Commercial paper — 35,226 — 35,226 U.S. government agency bonds — 27,472 — 27,472 State and municipal bonds — 15,215 — 15,215 Corporate bonds and notes — 200,661 — 200,661 $ 21,464 $ 278,574 $ — $ 300,038

Capital Structure

Capital Structure	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Capital Structure	Note 6. Capital Structure Preferred Stock The Company is authorized to issue 10,000,000 shares of preferred stock with a par value of $0.0001 per share. The Company’s Board is authorized to fix the voting rights, if any, designations, powers, preferences, the relative, participating, option or other special rights and any qualifications, limitations and restrictions thereof, applicable to the shares of each series. At December 31, 2024 and 2023, there were no shares of preferred stock issued and outstanding. Common Stock At December 31, 2024, the following shares of common stock were reserved for future issuance: Unexercised stock options outstanding under 2016 Equity Incentive Plan 188,229 Shares granted and unvested under 2020 Equity Incentive Plan 6,090,445 Authorized for future grant under 2024 Equity Incentive Plan 11,015,317 Authorized for future issuance under the Hyliion Holdings Corp. Employee Stock Purchase Plan 1,800,000 19,093,991 Treasury Stock In December 2023, we announced a share repurchase program which has no expiration date, authorizing the repurchase of up to $20.0 million in shares.

Share-Based Compensation

Share-Based Compensation	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Share-Based Compensation	Note 7. Share-Based Compensation 2024 Equity Incentive Plan On May 21, 2024, the Company’s shareholders approved a new long-term incentive award plan (the “2024 Plan”). The 2024 Plan is administered by the Board and the compensation committee. The selection of participants, allotment of shares, determination of price and other conditions are approved by the Board and the compensation committee at its sole discretion in order to attract and retain personnel instrumental to the success of the Company. Under the 2024 Plan, the Company may grant awards covering up to 8,000,000 shares of common stock, plus the amount of authorized but unissued shares under the 2020 Plan, the number of shares relating to awards under the 2020 Plan that are cancelled, lapsed, or are forfeited, and the number of shares withheld to satisfy a holder’s tax obligations. Grants under the 2024 Plan may be in the form of incentive stock options, nonstatutory stock options, stock appreciation rights, restricted stock awards, restricted stock unit awards, performance awards, and other awards to our employees, directors, and consultants. No stock options have been granted under the 2024 Plan. Employee and director restricted stock units (“RSUs”) for which a grant date has been established generally vest over one Activity in the 2024 Plan for the years ended December 31, 2024 and 2023 is summarized as follows: Number of Units Weighted Average Grant Date Fair Value (in Dollars) Unvested at December 31, 2023 — $ — Granted 232,176 1.81 Unvested at December 31, 2024 232,176 $ 1.81 Share-based compensation expense under the 2024 Plan for the years ended December 31, 2024 and 2023 was nil. The fair value of RSUs that vested during the years ended December 31, 2024 and 2023 was nil. There was $0.4 million of unrecognized compensation expense related to the 2024 Plan at December 31, 2024, which is expected to be recognized over the remaining vesting periods, subject to forfeitures, with a weighted-average period of 2.7 years. 2020 Equity Incentive Plan On October 1, 2020, the Company’s shareholders approved a new long-term incentive award plan (the “2020 Plan”) in connection with the business combination agreement and plan of reorganization, pursuant to which SHLL Merger Sub Inc., a Delaware corporation and wholly owned subsidiary of Tortoise Acquisition Corp., a Delaware corporation, merged with and into the Company on June 18, 2020. The 2020 Plan is administered by the Board and the compensation committee. The selection of participants, allotment of shares, determination of price and other conditions are approved by the Board and the compensation committee at its sole discretion in order to attract and retain personnel instrumental to the success of the Company. Under the 2020 Plan, the Company may grant an aggregate of 12,200,000 shares of common stock in the form of nonstatutory stock options, incentive stock options, SARs, restricted stock awards, performance awards and other awards. No stock options have been granted under the 2020 Plan. No further grants can be made under the 2020 Plan. We granted 2.7 million market-conditioned restricted stock units in 2024 that vested between February 13, 2025 and December 31, 2026 contingent upon achieving underlying closing stock price thresholds. Through December 31, 2024, there was achievement of underlying closing stock price thresholds on 100% of these awards which will vest between August 2025 and December 2026. These awards were valued at $0.83 per unit using fair value hierarchy Level III inputs including an underlying share volatility of 90% and a risk-free rate of 4.35%. Employee and director RSUs generally vest over one Activity in the 2020 Plan for the years ended December 31, 2024 and 2023 is summarized as follows: Number of Units Weighted Average Grant Date Fair Value (in Dollars) Unvested at December 31, 2022 1 2,769,100 $ 5.51 Granted 2 2,192,900 2.57 Vested (1,350,172) 5.28 Forfeited 3 (860,505) 4.53 Unvested at December 31, 2023 4 2,751,323 3.59 Granted 5,878,591 1.05 Vested (1,267,658) 3.87 Forfeited (1,271,811) 2.61 Unvested at December 31, 2024 6,090,445 $ 1.28 1 Excludes 1,336,667 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. 2 Excludes 25,000 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. 3 Excludes 59,584 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. 4 Excludes 633,750 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. These excluded shares were not granted during the year ended December 31, 2024. Share-based compensation expense under the 2020 Plan for the years ended December 31, 2024 and 2023 was $4.6 million and $6.2 million, respectively. The fair value of RSUs that vested during the years ended December 31, 2024 and 2023 was $2.3 million and $2.8 million, respectively. There was $4.6 million of unrecognized compensation expense related to the 2020 Plan at December 31, 2024, which is expected to be recognized over the remaining vesting periods, subject to forfeitures, with a weighted-average period of 1.8 years. 2016 Equity Incentive Plan The Hyliion Inc. 2016 Equity Incentive Plan (the “2016 Plan”), as amended in August 2017 and approved by the Board, permitted the granting of various awards including stock options (including both nonqualified options and incentive options), stock appreciation rights (“SARs”), stock awards, phantom stock units, performance awards and other share-based awards to employees, outside directors and consultants and advisors of the Company. Only stock options have been awarded to employees, consultants and advisors under the 2016 Plan. No further grants can be made under the 2016 Plan. Employee and nonemployee stock options generally vest over four years, with a maximum term of ten years from the date of grant. These awards become available to the recipient upon the satisfaction of a vesting condition based on a period of service. Activity in the 2016 Plan for the years ended December 31, 2024 and 2023 is summarized as follows: Number of Options Weighted Average Weighted Average Outstanding at December 31, 2022 2,541,439 $ 0.15 3.7 years Exercised (1,936,018) 0.13 Forfeited (82,450) 0.22 Outstanding at December 31, 2023 522,971 0.20 4.3 years Exercised (325,175) 0.21 Forfeited (9,567) 0.23 Outstanding at December 31, 2024 188,229 $ 0.20 4.7 years Exercisable at December 31, 2024 188,229 $ 0.20 4.7 years At December 31, 2024, the options outstanding and exercisable had an intrinsic value of $0.5 million and $0.3 million, respectively. There were no options with an exercise price greater than the market price on December 31, 2024 to exclude from the intrinsic value computation. The intrinsic value of options exercised during the years ended December 31, 2024 and 2023 was $0.4 million and $2.4 million, respectively. Share-based compensation expense under the 2016 Plan for the years ended December 31, 2024 and 2023 was nil and there was no unrecognized compensation expense related the 2016 Plan at December 31, 2024. Employee Stock Purchase Plan The Company has an authorized employee stock purchase plan (the “ESPP”) that would enable employees to contribute up to 15% of their base compensation toward the purchase of the Company’s common stock at 85% of its market value on the first or last day of each offering period. The ESPP was not implemented through December 31, 2024.

Leases

Leases	12 Months Ended
	Dec. 31, 2024
Leases [Abstract]
Leases	Note 8. Leases The Company enters into operating leases for its corporate office, temporary offices, vehicles and equipment. In addition, the Company may enter into arrangements whereby portions of the leased premises are subleased to third parties and are classified as operating leases. In December 2021, the Company amended the lease for its corporate office. This amendment increased the amount of space under the original lease, adjusted the monthly lease payments, and decreased the term of the lease to April 2027. The lease amendment includes the option to extend the term for up to two consecutive terms of three years, which was not reasonably certain to be exercised at the modification date. The Company’s corporate office lease has a term through 2027 and includes the option to extend the term for up to two consecutive terms of five years, which was not reasonably certain to be exercised at the commencement date. The following table provides a summary of the components of lease operating costs which are primarily included within R&D and selling, general and administrative expense: Year Ended December 31, 2024 2023 Operating lease costs: Operating lease cost $ 2,476 $ 2,239 Short-term lease cost 42 508 Variable lease cost 658 682 Total operating lease costs $ 3,176 $ 3,429 The following table provides the weighted-average lease terms and discount rates used for the Company’s operating leases: December 31, 2024 2023 Weighted-average remaining lease term: Operating leases 2.6 years 3.6 years Weighted-average discount rate: Operating leases 8.6 % 8.7 % The following table provides a summary of operating lease liability maturities for the next five years and thereafter at December 31, 2024: 2025 $ 2,900 2026 2,988 2027 1,426 2028 306 2029 — Thereafter — Total minimum lease payments 7,620 Less: imputed interest (828) Total lease obligations $ 6,792
Leases	Note 8. Leases The Company enters into operating leases for its corporate office, temporary offices, vehicles and equipment. In addition, the Company may enter into arrangements whereby portions of the leased premises are subleased to third parties and are classified as operating leases. In December 2021, the Company amended the lease for its corporate office. This amendment increased the amount of space under the original lease, adjusted the monthly lease payments, and decreased the term of the lease to April 2027. The lease amendment includes the option to extend the term for up to two consecutive terms of three years, which was not reasonably certain to be exercised at the modification date. The Company’s corporate office lease has a term through 2027 and includes the option to extend the term for up to two consecutive terms of five years, which was not reasonably certain to be exercised at the commencement date. The following table provides a summary of the components of lease operating costs which are primarily included within R&D and selling, general and administrative expense: Year Ended December 31, 2024 2023 Operating lease costs: Operating lease cost $ 2,476 $ 2,239 Short-term lease cost 42 508 Variable lease cost 658 682 Total operating lease costs $ 3,176 $ 3,429 The following table provides the weighted-average lease terms and discount rates used for the Company’s operating leases: December 31, 2024 2023 Weighted-average remaining lease term: Operating leases 2.6 years 3.6 years Weighted-average discount rate: Operating leases 8.6 % 8.7 % The following table provides a summary of operating lease liability maturities for the next five years and thereafter at December 31, 2024: 2025 $ 2,900 2026 2,988 2027 1,426 2028 306 2029 — Thereafter — Total minimum lease payments 7,620 Less: imputed interest (828) Total lease obligations $ 6,792

Property and Equipment, Net

Property and Equipment, Net	12 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Property and Equipment, Net	Note 9. Property and Equipment, Net Property and equipment, net at December 31, 2024 and 2023 is summarized as follows: December 31, 2024 2023 Production machinery and equipment $ 27,846 $ 10,376 Vehicles 379 2,013 Leasehold improvements 4,313 2,236 Office furniture and fixtures 270 223 Computers and related equipment 2,113 1,963 34,921 16,811 Less: accumulated depreciation (9,001) (6,824) Total property and equipment, net $ 25,920 $ 9,987 Depreciation expense for the years ended December 31, 2024 and 2023 totaled approximately $3.1 million and $3.2 million, respectively. For the year ended December 31, 2024, $0.4 million and $2.7 million was included in selling, general and administrative expenses and R&D expenses, respectively, in the consolidated statements of operations. For the year ended December 31, 2023, $0.6 million, $1.7 million, and $0.9 million was included in selling, general and administrative expenses, R&D expenses and exit and termination costs, respectively, in the co nsolidated statements of operations.

Accrued Expenses and Other Curr

Accrued Expenses and Other Current Liabilities	12 Months Ended
	Dec. 31, 2024
Accrued Liabilities and Other Liabilities [Abstract]
Accrued Expenses and Other Current Liabilities	Note 10. Accrued Expenses and Other Current Liabilities Accrued expenses and other current liabilities at December 31, 2024 and 2023 are summarized as follows: December 31, 2024 2023 Accrued professional services and other $ 1,823 $ 2,606 Accrued compensation and related benefits 3,280 1,510 Other accrued liabilities 746 1,922 Accrued severance, contract termination, and other charges 773 4,013 $ 6,622 $ 10,051

Income Taxes

Income Taxes	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Income Taxes	Note 11. Income Taxes The income tax provision for the years ended December 31, 2024 and 2023 is summarized as follows: Year Ended December 31, 2024 2023 Current tax expense: Federal $ — $ — State — — Total current tax expense $ — $ — Deferred tax (benefit) expense: Federal $ (10,493) $ (25,328) State — — Valuation allowance 10,493 25,328 Total deferred tax expense $ — $ — The components of deferred taxes at December 31, 2024 and 2023 are summarized as follows: December 31, 2024 2023 Deferred tax assets: Federal net operating loss carryforwards $ 72,697 $ 62,561 State net operating loss carryforwards 491 491 Operating lease obligation 1,426 1,604 Section 174 expenditures 28,445 26,444 R&D tax credit 4,714 4,714 Other 1,676 3,235 Intangible assets, net 5,159 5,522 Total deferred tax assets 114,608 104,571 Less: valuation allowance (113,296) (102,803) Deferred tax assets, net of valuation allowance 1,312 1,768 Deferred tax liabilities: Operating lease right of use asset, net 1,140 1,485 Property and equipment, net 172 283 Total deferred tax liabilities 1,312 1,768 Net deferred tax assets $ — $ — The reconciliation of taxes at the federal statutory rate to the Company’s provision for income taxes for the years ended December 31, 2024 and 2023 is summarized as follows: Year Ended December 31, 2024 2023 Provision at statutory rate of 21% $ (10,930) $ (25,937) Other 437 609 Change in valuation allowance 10,493 25,328 $ — $ — In assessing the realizability of deferred tax assets, management considered whether it is more likely than not that some portion or all of the deferred tax assets will not be realized. The ultimate realization of deferred tax assets is dependent upon the generation of future taxable income during the periods in which those temporary differences become deductible. Management considere d the scheduled reversal of deferred tax liabilities, projected future taxable income and tax planning strategies in making this assessment. Based upon the level of historical taxable income and projections for future taxable income over the periods in which the deferred tax assets are deductible, management believes it is more likely than not that the Company will not realize the benefits of these deductible differences at December 31, 2024. The Company had federal net operating loss carryforwards of $346.2 million and $297.9 million at December 31, 2024 and 2023, respectively. At December 31, 2024, $10.5 million of this amount will begin to expire in 2036 and the remaining $335.7 million has an indefinite carryforward period. The Company had state net operating loss carryforwards of $12.5 million and $12.5 million at December 31, 2024 and 2023, respectively, that will begin to expire beginning in 2036. The Company had federal and state R&D credits of $4.7 million that will begin to expire in 2037. The Company’s ability to utilize a portion of net operating loss carryforwards and credits to offset future taxable income, and tax, respectively, is subject to certain limitations under Section 382 of the Internal Revenue Code upon changes in equity ownership of the Company. Due to such limitation, $2.0 million of the Company’s net operating loss and less than $0.1 million of the Company’s R&D credits will expire unused, regardless of taxable income in future years. The Company files a United States federal income tax return, as well as income tax returns in various states. The tax returns for years 2021 and thereafter remain open for examination. However, the taxing authorities have the ability to review the propriety of tax losses created in closed tax years to the extent such losses are utilized in an open tax year.

Commitments and Contingencies

Commitments and Contingencies	12 Months Ended
	Dec. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Commitments and Contingencies	Note 12. Commitments and Contingencies Economic Incentive Agreement During the quarter ended March 31, 2024, in connection with our operations in Cedar Park, Texas, the Company entered into an agreement with the Cedar Park Economic Development Corporation (“EDC”) that superseded prior agreements, whereby the Company would receive cash grants up to $1.1 million from the EDC at various measurement dates during the term of the agreement contingent upon the Company fulfilling and maintaining certain occupancy, investment, and employment requirements. The requirements must be met on or be fore specific measurement dates and maintained throughout the term of the agreement, which expires effective December 31, 2029. The Company has received payments to date of $0.4 million which are refundable as applicable performance requirements were not met and are included within accrued expenses and other current liabilities e EDC has the right to file a security interest to all assets of the Company. Legal Proceedings The Company is periodically involved in legal proceedings, legal actions and claims arising in the nor mal course of business, including proceedings relating to product liability, intellectual property, safety and health, employment and other matters. The Company believes that the outcome of such legal proceedings, legal actions and claims will not have a significant adverse effect on the Company’s financial position, results of operations or cash flows.

Net Loss Per Share

Net Loss Per Share	12 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Net Loss Per Share	Note 13. Net Loss Per Share The computation of basic and diluted net loss per share for the years ended December 31, 2024 and 2023 is summarized as follows (in thousands, except share and per share data): Year Ended December 31, 2024 2023 Numerator: Net loss attributable to common stockholders $ (52,048) $ (123,510) Denominator: Weighted average shares outstanding, basic and diluted 174,915,487 181,411,069 Net loss per share, basic and diluted $ (0.30) $ (0.68) Potential common shares excluded from the computation of diluted net loss per share because including them would have had an anti-dilutive effect for the years ended December 31, 2024 and 2023 are summarized as follows: Year Ended December 31, 2024 2023 Unexercised stock options 188,229 522,971 Unvested restricted stock units 6,322,621 3,385,073 6,510,850 3,908,044

Supplemental Cash Flow Informat

Supplemental Cash Flow Information	12 Months Ended
	Dec. 31, 2024
Supplemental Cash Flow Elements [Abstract]
Supplemental Cash Flow Information	Note 14. Supplemental Cash Flow Information Supplemental cash flow information for the years ended December 31, 2024 and 2023 is summarized as follows: Year Ended December 31, 2024 2023 Cash paid for interest $ — $ — Cash paid for taxes $ — $ — Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases, net $ (1,687) $ (2,470) Right-of-use assets obtained in exchange for lease obligations $ — $ 2,096 Year Ended December 31, 2024 2023 Supplemental disclosure of noncash investing and financing activities: Repurchase of treasury stock included in accrued expenses and other current liabilities $ 117 $ — Acquisitions of property and equipment and intangible assets included in accounts payable and accrued expenses and other current liabilities $ 3,884 $ 292

Retirement Plan

Retirement Plan	12 Months Ended
	Dec. 31, 2024
Retirement Benefits [Abstract]
Retirement Plan	Note 15. Retirement Plan The Company has adopted a 401(k) plan to provide all eligible employees a means to accumulate retirement savings on a tax-advantaged or post-tax basis. The 401(k) plan eligibility conditions require participants are at least 21 years old to participate. Eligibility entry date is the first of the month following date of hire, or the first of the month following the date the employee turns 21 years old. Plan participants may make elective contributions up to the maximum percentage of compensation and dollar amount allowed under the Internal Revenue Code and are always 100% vested in their elective contributions. The Company has also established a Profit Sharing plan in which the employer may make contributions on the employee’s behalf (“discretionary employer contributions”). The Company did not make any Profit Sharing contributions during the years ended December 31, 2024 and 2023.

Pay vs Performance Disclosure

Pay vs Performance Disclosure - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Pay vs Performance Disclosure
Net Income (Loss)	$ (52,048)	$ (123,510)

Insider Trading Arrangements

Insider Trading Arrangements	3 Months Ended
	Dec. 31, 2024
Trading Arrangements, by Individual
Rule 10b5-1 Arrangement Adopted	false
Non-Rule 10b5-1 Arrangement Adopted	false
Rule 10b5-1 Arrangement Terminated	false
Non-Rule 10b5-1 Arrangement Terminated	false

Insider Trading Policies and Pr

Insider Trading Policies and Procedures	12 Months Ended
	Dec. 31, 2024
Insider Trading Policies and Procedures [Line Items]
Insider Trading Policies and Procedures Adopted	true

Cybersecurity Risk Management a

Cybersecurity Risk Management and Strategy Disclosure	12 Months Ended
	Dec. 31, 2024
Cybersecurity Risk Management, Strategy, and Governance [Line Items]
Cybersecurity Risk Management Processes for Assessing, Identifying, and Managing Threats [Text Block]	Our cybersecurity risk management program leverages the National Institute of Standards and Technology (“NIST”) 800-37 framework as a foundation, customized to align with our entity size, risk profile, and industry best practices. We believe that leveraging the NIST framework as a foundation ensures a balanced approach for mitigating vulnerabilities while maintaining operational efficiency. We maintain a comprehensive incident response plan with clearly defined roles and responsibilities. In the event of an incident, the plan outlines notification procedures, containment measures, eradication steps, and recovery processes. We also conduct annual reviews to ensure the plan’s effectiveness. We conduct annual cybersecurity assessments and implement controls around any deficiencies in security that are identified, engaging third-party consultants to assist which include tabletop exercises to ensure that our incident management processes function as intended. This assessment covers entity-level controls, threat management, and reviews of critical third-party security measures. Materiality of individual cybersecurity incidents is determined by a comprehensive assessment framework considering, but not limited to, the following factors: • Impact on Business Operations: Potential disruptions to critical systems, services, or financial transactions. • Data Sensitivity: The nature and sensitivity of the data involved, with incidents concerning personally identifiable information or highly confidential data deemed more material. • Regulatory Compliance: Potential violations of cybersecurity laws, regulations, or industry standards. • Reputational Risk: Harm to the Company’s reputation, customer trust, and brand value. • Legal Obligations: Legal requirements for reporting incidents and potential consequences of non-compliance. Identification, Assessment, and Reporting of Cybersecurity Threats We employ a multi-layered approach to identify, assess, and report potential cybersecurity threats: • Threat intelligence tracking: We actively monitor relevant-threat intelligence feeds and industry best practices to stay informed about emerging threats and vulnerabilities. • Managed Detection and Response (“MDR”) partnership: We have partnered with a reputable third-party MDR provider to enhance our threat detection and response capabilities. This service provides continuous monitoring, analysis, and proactive response to potential threats, ensuring timely identification and mitigation of cybersecurity incidents. • Metrics and Measurements: We capture telemetry from our IT infrastructure in order to measure the effectiveness of our security controls and identify areas for improvement.
Cybersecurity Risk Management Processes Integrated [Flag]	true
Cybersecurity Risk Management Processes Integrated [Text Block]	We maintain a comprehensive incident response plan with clearly defined roles and responsibilities. In the event of an incident, the plan outlines notification procedures, containment measures, eradication steps, and recovery processes. We also conduct annual reviews to ensure the plan’s effectiveness. We conduct annual cybersecurity assessments and implement controls around any deficiencies in security that are identified, engaging third-party consultants to assist which include tabletop exercises to ensure that our incident management processes function as intended. This assessment covers entity-level controls, threat management, and reviews of critical third-party security measures. Materiality of individual cybersecurity incidents is determined by a comprehensive assessment framework considering, but not limited to, the following factors: • Impact on Business Operations: Potential disruptions to critical systems, services, or financial transactions. • Data Sensitivity: The nature and sensitivity of the data involved, with incidents concerning personally identifiable information or highly confidential data deemed more material. • Regulatory Compliance: Potential violations of cybersecurity laws, regulations, or industry standards. • Reputational Risk: Harm to the Company’s reputation, customer trust, and brand value. • Legal Obligations: Legal requirements for reporting incidents and potential consequences of non-compliance. Identification, Assessment, and Reporting of Cybersecurity Threats We employ a multi-layered approach to identify, assess, and report potential cybersecurity threats: • Threat intelligence tracking: We actively monitor relevant-threat intelligence feeds and industry best practices to stay informed about emerging threats and vulnerabilities. • Managed Detection and Response (“MDR”) partnership: We have partnered with a reputable third-party MDR provider to enhance our threat detection and response capabilities. This service provides continuous monitoring, analysis, and proactive response to potential threats, ensuring timely identification and mitigation of cybersecurity incidents. • Metrics and Measurements: We capture telemetry from our IT infrastructure in order to measure the effectiveness of our security controls and identify areas for improvement.
Cybersecurity Risk Management Third Party Engaged [Flag]	true
Cybersecurity Risk Third Party Oversight and Identification Processes [Flag]	true
Cybersecurity Risk Materially Affected or Reasonably Likely to Materially Affect Registrant [Flag]	false
Cybersecurity Risk Board of Directors Oversight [Text Block]	The Company’s Chief Financial Officer (“CFO”) and the audit committee of the board of directors of the Company (the “Board”) has responsibility for the oversight of cybersecurity threats and incidents. The audit committee conducts periodic reviews of the Company’s cybersecurity programs, policies, and risk management strategies to ensure alignment with industry best practices. Additionally, our CFO, leveraging extensive experience in managing technology infrastructure and cybersecurity risk, performs internal reviews with operational teams to assess cybersecurity readiness and enhance incident response strategies. The Board’s oversight is further strengthened by the presence of a director with over 30 years of experience advising global companies on technology and operations, including cybersecurity risk management. Our internal IT team, with over 40 years combined experience in cybersecurity, plays a critical role in implementing security controls, threat monitoring, and incident response. This multi-tiered governance structure ensures that cybersecurity remains a top priority at both the executive and operational levels.
Cybersecurity Risk Board Committee or Subcommittee Responsible for Oversight [Text Block]	The Company’s Chief Financial Officer (“CFO”) and the audit committee of the board of directors of the Company (the “Board”) has responsibility for the oversight of cybersecurity threats and incidents. The audit committee conducts periodic reviews of the Company’s cybersecurity programs, policies, and risk management strategies to ensure alignment with industry best practices.
Cybersecurity Risk Process for Informing Board Committee or Subcommittee Responsible for Oversight [Text Block]	We have a communication process for incidents based on their severity as outlined in our incident response plan. When a major incident is detected, executive leadership is informed within 24 hours. The audit committee and Chief Financial Officer are notified, and a detailed report is submitted, within 24-48 hours. For moderate incidents, the notification timeframe is 72 hours, and the detailed report is submitted to the audit committee within five to seven days. If a cybersecurity incident is deemed material, it will be reported promptly under SEC guidance.
Cybersecurity Risk Role of Management [Text Block]	The Company’s Chief Financial Officer (“CFO”) and the audit committee of the board of directors of the Company (the “Board”) has responsibility for the oversight of cybersecurity threats and incidents. The audit committee conducts periodic reviews of the Company’s cybersecurity programs, policies, and risk management strategies to ensure alignment with industry best practices. Additionally, our CFO, leveraging extensive experience in managing technology infrastructure and cybersecurity risk, performs internal reviews with operational teams to assess cybersecurity readiness and enhance incident response strategies. The Board’s oversight is further strengthened by the presence of a director with over 30 years of experience advising global companies on technology and operations, including cybersecurity risk management. Our internal IT team, with over 40 years combined experience in cybersecurity, plays a critical role in implementing security controls, threat monitoring, and incident response. This multi-tiered governance structure ensures that cybersecurity remains a top priority at both the executive and operational levels.
Cybersecurity Risk Management Positions or Committees Responsible [Flag]	true
Cybersecurity Risk Management Positions or Committees Responsible [Text Block]	The Company’s Chief Financial Officer (“CFO”) and the audit committee of the board of directors of the Company (the “Board”) has responsibility for the oversight of cybersecurity threats and incidents. The audit committee conducts periodic reviews of the Company’s cybersecurity programs, policies, and risk management strategies to ensure alignment with industry best practices. Additionally, our CFO, leveraging extensive experience in managing technology infrastructure and cybersecurity risk, performs internal reviews with operational teams to assess cybersecurity readiness and enhance incident response strategies. The Board’s oversight is further strengthened by the presence of a director with over 30 years of experience advising global companies on technology and operations, including cybersecurity risk management. Our internal IT team, with over 40 years combined experience in cybersecurity, plays a critical role in implementing security controls, threat monitoring, and incident response. This multi-tiered governance structure ensures that cybersecurity remains a top priority at both the executive and operational levels.
Cybersecurity Risk Management Expertise of Management Responsible [Text Block]	Additionally, our CFO, leveraging extensive experience in managing technology infrastructure and cybersecurity risk, performs internal reviews with operational teams to assess cybersecurity readiness and enhance incident response strategies. The Board’s oversight is further strengthened by the presence of a director with over 30 years of experience advising global companies on technology and operations, including cybersecurity risk management. Our internal IT team, with over 40 years combined experience in cybersecurity, plays a critical role in implementing security controls, threat monitoring, and incident response.
Cybersecurity Risk Process for Informing Management or Committees Responsible [Text Block]	We have a communication process for incidents based on their severity as outlined in our incident response plan. When a major incident is detected, executive leadership is informed within 24 hours. The audit committee and Chief Financial Officer are notified, and a detailed report is submitted, within 24-48 hours. For moderate incidents, the notification timeframe is 72 hours, and the detailed report is submitted to the audit committee within five to seven days.
Cybersecurity Risk Management Positions or Committees Responsible Report to Board [Flag]	true

Summary of Significant Accoun_2

Summary of Significant Accounting Policies (Policies)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Basis of Presentation and Principles of Consolidation	Basis of Presentation and Principles of Consolidation The accompanying consolidated financial statements include the accounts of Hyliion Holdings Corp. and its wholly owned subsidiary. Intercompany transactions and balances have been eliminated upon consolidation. The consolidated financial statements and accompanying notes have been prepared in a ccordance with accounting principles generally accepted in the United States of America (“GAAP”) and in accordance with the rules and regulations of the Unites States Securities and Exchange Commission (“SEC”). Any reference in these footnotes to the applicable guidance is meant to refer to the authoritative GAAP as found in the Accounting Standards Codification and Accounting Standards Updates (“ASU”) of the Financial Accounting Standards Board (“FASB”).
Use of Estimates	Use of Estimates The preparation of financial statements in conformity with GAAP requires management to make certain estimates and assumptions that affect the reported amounts of assets and liabilities and disclosure of contingent assets and liabilities as of the balance sheet date, as well as reported amounts of expenses during the reporting period. The Company’s most significant estimates and judgments involve revenue, assets held for sale, income taxes and valuation of share-based compensation. Management bases its estimates on historical experience and on various other assumptions believed to be reasonable, the results of which form the basis for making judgments about the carrying values of assets and liabilities. Actual results could differ from those estimates, and such differences could be material to the Company’s consolidated financial statements.
Segment Information	Segment Information ASC 280, Segment Reporting , defines operating segments as components of an enterprise where discrete financial information is available that is evaluated regularly by the chief operating decision-maker (“CODM”) in deciding how to allocate resources and in assessing performance. The Company operates as a single operating segment from which all revenue and net income (loss) is derived and for which all assets are attributed. The Company’s CODM is the chief executive officer, who has ultimate responsibility for the operating performance of the Company and the allocation of resources. The CODM uses net income (loss) to manage the business and does not segment the business for internal reporting or decision making.
Concentration of Supplier Risk	Concentration of Supplier Risk The Company is dependent on certain suppliers, the majority of which are single source suppliers, and the inability of these suppliers to deliver necessary components of the Company’s products in a timely manner at prices, quality levels and volumes that are acceptable, or the Company’s inability to efficiently manage these components from these suppliers, could have a material adverse effect on the Company’s business, prospects, financial condition and operating results.
Cash and Cash Equivalents	Cash and Cash Equivalents The Company considers all highly liquid investments with a maturity date of 90 days or less at the time of purchase to be cash and cash equivalents only if in checking, savings or money market accounts. Cash and cash equivalents include cash held in banks and money market accounts and are carried at cost, which approximates fair value. The Company maintains cash in excess of federally insured limits at financial institutions which it believes are of high credit quality and has not incurred any losses related to these balances to date. The Company believes its credit risk, with respect to these financial institutions to be minimal.
Accounts Receivable	Accounts Receivable
Investments	Investments The Company’s investments consist of corporate bonds, U.S. treasury and agency securities, state and local municipal bonds and commercial paper, all of which are classified as held-to-maturity, with a maturity date of 36-months or less at the time of purchase. The Company determines the appropriate classification of investments at the time of purchase and re-evaluates such designation as of each balance sheet date. Investments are classified as held-to-maturity when the Company has the positive intent and ability to hold the securities to maturity. Held-to-maturity securities are stated at amortized cost, adjusted for amortization of premiums and accretion of discounts to maturity. Such amortization, along with interest, is included in interest income. The Company uses the specific identification method to determine the cost basis of securities sold. Investments are impaired when a decline in fair value is judged to be other-than-temporary. The Company evaluates investments for impairment by considering the length of time and extent to which market value has been less than cost or amortized cost, the financial condition and near-term prospects of the issuer as well as specific events or circumstances that may influence the operations of the issuer and the Company’s intent to sell the security or the likelihood that it will be required to sell the security before recovery of the entire amortized cost. Once a decline in fair value is determined to be other-than-temporary, an impairment charge is recorded to other income (expense) and a new cost basis in the investment is established.
Fair Value Measurements	Fair Value Measurements ASC 820, Fair Value Measurements , clarifies that fair value is an exit price, representing the amount that would be received to sell an asset or paid to transfer a liability in an orderly transaction between market participants. As such, fair value is a market-based measurement that should be determined based upon assumptions that market participants would use in pricing an asset or liability. As a basis for considering such assumptions, ASC 820 establishes a three-tier fair value hierarchy, which prioritizes the inputs used in measuring fair value as follows: Level I : Quoted prices (unadjusted) for identical assets or liabilities in active markets that the Company can access at the measurement date; Level II : Significant other observable inputs other than level I prices such as quoted prices for similar assets or liabilities, quoted prices in markets that are not active or other inputs that are observable or can be corroborated by observable market data; and Level III : Significant unobservable inputs that reflect the Company’s own assumptions about the assumptions that market participants would use in pricing an asset or liability. An asset’s or liability’s fair value measurement level within the fair value hierarchy is based on the lowest level of any input that is significant to the fair value measurement. Valuation techniques used need to maximize the use of observable inputs and minimize the use of unobservable inputs. The Company believes its valuation methods are appropriate and consistent with other market participants, however the use of different methodologies or assumptions to determine the fair value of certain financial instruments could result in a different fair value measurement at the reporting date. The Company’s financial instruments consist of cash and cash equivalents and restricted cash, accounts receivable, investments, accounts payable and accrued expenses. The carrying value of cash and cash equivalents and restricted cash, accounts receivable, accounts payable and accrued expenses approximate fair value because of the short-term nature of those instruments. The fair value of investments is based on quoted prices for identical or similar instruments in markets that are not active. As a result, investments are classified within Level II of the fair value hierarchy.
Inventories	Inventories Through December 31, 2024, we have not yet commercialized the KARNO generator. Costs incurred for components acquired prior to our determination of reaching a commercial stage are expensed as R&D costs, resulting in zero cost basis for those components. As a result, moving-average prices for inventory that is capitalized in future periods may be significantly affected by those zero cost items. Inventory is consumed in the performance of contracts for R&D services in the quarter in which it is purchased, including certain allocations of overhead costs, and we therefore do not record inventory at each reporting period pertaining to these contracts.
Prepaid Expenses and Other Current Assets	Prepaid Expenses and Other Current Assets Prepaid expenses and other current assets include prepaid insurance, rent and supplies, which are expected to be recognized, received or realized within the next 12 months.
Property and Equipment, Net	Property and Equipment, Net Property and equipment, net is stated at cost less accumulated depreciation, or if acquired in a business combination, at allocated fair value at the date of acquisition. Depreciation is calculated using the straight-line method, based upon the following estimated useful lives: Production machinery and equipment 2 to 12 years Vehicles 3 to 7 years Leasehold improvements shorter of lease term or 7 years Furniture and fixtures 3 years Computers and related equipment 3 to 7 years Major renewals and improvements are capitalized, while replacements, maintenance and repairs, which do not improve or extend the lives of the respective assets, are expensed as incurred. When property and equipment is retired or otherwise disposed of, the related cost and accumulated depreciation are removed from the accounts, and any gain or loss on the disposition is recorded in the consolidated statement of operations as a component of other income (expense). All long-lived assets are located in the U.S.
Impairment of Long-Lived Assets	Impairment of Long-Lived Assets The Company reviews long-lived assets, including property and equipment and intangible assets with definite lives, for impairment whenever events or changes in circumstances indicate that an asset group’s carrying amount may not be recoverable. The Company conducts its long-lived asset impairment analysis in accordance with ASC 360-10, Impairment or Disposal of Long-Lived Assets , which requires the Company to group assets and liabilities at the lowest level for which identifiable cash flows are largely independent of the cash flows of other assets and liabilities and evaluate the asset group against the sum of the undiscounted future cash flows. If the undiscounted cash flows do not indicate the carrying amount of the asset group is recoverable, an impairment charge is measured as the amount by which the carrying amount of the asset group exceeds its fair value.
Revenue	Revenue The Company follows five steps to recognize revenue from contracts with customers under ASC 606, Revenue from Contracts with Customers, which are: • Step 1: Identify the contract(s) with a customer; • Step 2: Identify the performance obligations in the contract; • Step 3: Determine the transaction price; • Step 4: Allocate the transaction price to the performance obligations in the contract; and • Step 5: Recognize revenue when (or as) a performance obligation is satisfied. Product Sales The Company has historically generated revenues from sales of hybrid systems for Class 8 semi-trucks and limited quantities of Class 8 semi-trucks outfitted with the hybrid system. We recognized revenue on Hybrid system sales and Class 8 semi-trucks outfitted with Hybrid systems upon delivery to, and acceptance of the vehicle by, the customer, which is when control transferred. Contracts were reviewed for significant financing components and payments were typically received within 30 days of delivery. The sale of a Hybrid system to an end-use fleet customer consisted of a completed modification to the customer vehicle and the installation services involved significant integration of the Hybrid system with the customer’s vehicle. Installation services were not distinct within the context of the contract and together with the sale of the Hybrid system represented a single performance obligation. We did not offer any sales returns. Amounts billed to customers related to shipping and handling were classified as revenue, and we elected to recognize the cost for freight and shipping when control transferred to the customer as a cost of revenue. Our policy was to exclude taxes collected from customers from the transaction price of contracts. The Company has discontinued the electrified powertrain systems business and shifted to focus on the development and commercialization of the fuel-agnostic KARNO generator technology. U.S. Government Contracts The Company was performing under two contracts as both a prime and subcontractor to the United States government to provide R&D services. The larger of these two contracts was modified and accounted for as a new contract in the quarter ending December 31, 2024. These contracts were not accounted for as revenue prior to September 30, 2024 as they were not in the ordinary course of business and the counterparties were not customers under GAAP. In September 2024, the Company was awarded a best effort cost-plus-fixed fee contract up to $16.0 million by the United States Department of the Navy’s Office of Naval Research (“ONR”) to research the suitability of its KARNO generator for Navy ships and stationary power applications. Under the agreement, the Company will provide R&D services through September 2026, including delivery of up to seven KARNO generators. The ONR contract represented a significant change in business strategy toward providing R&D activities in the ordinary course of business in addition to developing power generators for stationary and mobile applications. The Company now accounts for all three contracts under ASC 606 beginning in the quarter ending December 31, 2024. The remaining amounts of revenue that we may recognize under these contracts was up to $15.7 million as of December 31, 2024, which is expected to be recognized in 2025 and 2026. There is a single research and development services performance obligation in each of these contracts that is measured over time as the services are performed. The Company generally invoices monthly which corresponds directly with the value to the customers of the performance completed to date, and recognizes revenue in the amount that it has a right to invoice. Payment is ordinarily due within 90 days of invoice submission. Cost of R&D services revenue includes labor, allocated fringe and overhead, and inventory.
Leases	Leases We determine if an arrangement is a lease at inception of the contract. Operating leases are included in operating lease right-of-use (“ROU”) assets, current portion of operating lease liabilities, and operating lease liabilities, net of current portion in the accompanying consolidated balance sheets. We have lease agreements with lease and non-lease components, and have elected to utilize the practical expedient to account for lease and non-lease components together as a single combined lease component. Variable lease costs consist primarily of common area maintenance. ROU assets represent the Company’s right to use underlying assets for the lease term, and lease liabilities represent the Company’s obligation to make lease payments arising from the leases. ROU assets and lease liabilities are recognized at the commencement date based on the present value of lease payments over the lease term. The discount rate used to calculate the present value for lease payments is the Company’s incremental borrowing rate, which is determined based on information available at lease commencement and is equal to the rate of interest that the Company would have to pay to borrow on a collateralized basis over a similar term in an amount equal to the lease payments in a similar economic environment. The Company uses the implicit rate when readily determinable. The Company’s real estate leases may include one or more options to renew, with the renewal extending the lease term for an additional one
Marketing, Promotional and Advertising Costs	Marketing, Promotional and Advertising Costs
Research and Development Expense	Research and Development Expense R&D costs did not meet the requirements to be recognized as an asset as the associated future benefits were at best uncertain and there was no alternative future use at the time the costs were incurred. R&D costs include, but are not limited to, outsourced engineering services, allocated facilities costs, depreciation on equipment utilized in R&D activities, internal engineering and development expenses, materials, internally-developed software and employee related expenses (including salaries, benefits, travel, and share-based compensation) related to development of the Company’s products and services.
Share-Based Compensation	Share-Based Compensation The Company accounts for share-based compensation in accordance with ASC 718, Compensation – Stock Compensation , under which shared based payments that involve the issuance of common stock to employees and nonemployees and meet the criteria for equity-classified awards are recognized in the financial statements as share-based compensation expense based on the fair value on the date of grant. The Company issues restricted stock awards to employees and nonemployees, utilizing new shares. The Company has elected to recognize the adjustment to share-based compensation expense in the period in which forfeitures occur. We recognize compensation expense for awards with only service conditions on a straight-line basis over the requisite service period for the entire award. If factors change, and we utilize different assumptions including the probability of achieving performance conditions, share-based compensation cost on future award grants may differ significantly from share-based compensation cost recognized on past award grants. If there are any modifications or cancellations of the underlying unvested securities, we may be required to accelerate any remaining unearned share-based compensation cost or incur incremental cost. Share-based compensation cost primarily affects our R&D and selling, general and administrative expenses.
Income Taxes	Income Taxes The Company accounts for income taxes in accordance with ASC 740, Income Taxes , under which deferred tax liabilities and assets are recognized for the expected future tax consequences of temporary differences between financial statement carrying amounts and the tax basis of assets and liabilities and net operating loss and tax credit carryforwards. Valuation allowances are established when necessary to reduce deferred tax assets to the amount expected to be realized. Due to the Company’s history of losses since inception, the net deferred tax assets have been fully offset by a valuation allowance at December 31, 2024 and 2023. Uncertain tax positions taken or expected to be taken in a tax return are accounted for using the more likely than not threshold for financial statement recognition and measurement. For the years ended December 31, 2024 and 2023, there were no uncertain tax positions taken or expected to be taken in the Company’s tax returns.
Net Loss Per Share	Net Loss Per Share Basic loss per share (“EPS”) is computed by dividing net loss (the numerator) by the weighted average number of common shares outstanding for the period (the denominator). Diluted EPS attributable to common shareholders is computed by adjusting net loss by the weighted average number of common shares and potential common shares outstanding (if dilutive) during each period. Potential common shares include shares issuable upon exercise of stock options and vesting of restricted stock awards (see Note 7). The number of potential common shares outstanding are calculated using the treasury stock or if-converted method.
Recent Accounting Pronouncements	Recent Accounting Pronouncements In November 2024, the FASB issued ASU 2024-03, Income Statement—Reporting Comprehensive Income—Expense Disaggregation Disclosures (Subtopic 220-40), and clarified by ASU 2025-01, to enable investors to better understand the major components of an entity’s income statement. The pronouncement is effective for fiscal years beginning after December 15, 2026 and interim periods beginning after December 15, 2027 and we expect a material impact to our disclosures as a result of adoption. In December 2023, the FASB issued ASU 2023-09, Income Taxes (Topic 740) , to enhance transparency and decision usefulness of income tax disclosures. The pronouncement is effective for fiscal years beginning after December 15, 2024 and we expect a material impact to our disclosures as a result of adoption. In November 2023, the FASB issued ASU 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures , to improve the disclosures about a public entity’s reportable segments. The pronouncement is effective for fiscal years beginning after December 15, 2023 and interim periods within fiscal years beginning after December 15, 2024. The Company adopted ASU 2023-07 for the year ended December 31, 2024 and updated its related disclosures.

Disposals (Tables)

Disposals (Tables)	12 Months Ended
	Dec. 31, 2024
Business Combination, Asset Acquisition, and Joint Venture Formation [Abstract]
Schedule of Changes in Plan Liabilities	The change in total liabilities associated with the Plan is included within accrued expenses and other current liabilities as presented in Note 10 , and accounts payable, and is summarized as follows (in millions): December 31, 2023 Charged to Expense (Benefit) Costs Paid or Settled December 31, 2024 Employee severance and retention $ 1.1 $ — $ (1.0) $ 0.1 Contract terminations 6.5 (0.8) (5.1) 0.6 Warranty obligations 0.4 (0.3) — 0.1 $ 8.0 $ (1.1) $ (6.1) $ 0.8 December 31, 2022 Charged to Expense Costs Paid or Settled December 31, 2023 Employee severance and retention $ — $ 1.2 $ (0.1) $ 1.1 Contract terminations — 8.2 (1.7) 6.5 Warranty obligations 0.5 0.1 (0.2) 0.4 $ 0.5 $ 9.5 $ (2.0) $ 8.0

Summary of Significant Accoun_3

Summary of Significant Accounting Policies (Tables)	12 Months Ended
	Dec. 31, 2024
Accounting Policies [Abstract]
Schedule of Restrictions on Cash and Cash Equivalents	Total cash and cash equivalents and restricted cash as presented in the consolidated statements of cash flows is summarized as follows: December 31, 2024 December 31, 2023 December 31, 2022 Cash and cash equivalents $ 9,227 $ 12,881 $ 119,468 Restricted cash included in prepaid expenses and other current assets — 7,918 — Restricted cash included in other assets 665 665 665 $ 9,892 $ 21,464 $ 120,133
Schedule of Significant Customers	The portion of our revenues from significant customers is summarized as follows and is attributable to the U.S.: Year Ended December 31, 2024 2023 Customer A 88 % — % Customer B 12 — Customer C — 65 Customer D — 25 100 % 90 %
Schedule of Estimated Useful Lives	Depreciation is calculated using the straight-line method, based upon the following estimated useful lives: Production machinery and equipment 2 to 12 years Vehicles 3 to 7 years Leasehold improvements shorter of lease term or 7 years Furniture and fixtures 3 years Computers and related equipment 3 to 7 years
Schedule of Significant Expense Categories	The significant expense categories and amounts that are regularly provided to the CODM and included in the reported measure of segment loss for the years ended December 31, 2024 and 2023 are summarized as follows (in millions): Year Ended December 31, 2024 2023 Total revenues $ 1.5 $ 0.7 Total cost of revenues 1.4 1.7 Gross profit (loss) 0.1 (1.0) Administrative and office 7.7 12.4 Depreciation and amortization 3.1 2.4 Facilities 5.1 5.0 Personnel 24.3 46.7 Product development, exclusive of other costs presented 15.0 34.0 Professional services 5.2 21.7 Exit and termination costs 3.0 11.5 Other operating expense 1.0 2.6 Total operating expenses 64.4 136.3 Other income, net 12.3 13.8 Net loss $ (52.0) $ (123.5)

Investments (Tables)

Investments (Tables)	12 Months Ended
	Dec. 31, 2024
Investments, Debt and Equity Securities [Abstract]
Schedule of Amortized Cost, Unrealized Gains and Losses, and Fair Value	The amortized cost, unrealized gains and losses, and fair value, and maturities of our held-to-maturity investments at December 31, 2024 and 2023 are summarized as follows: Fair Value Measurements at December 31, 2024 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Commercial paper $ 979 $ 3 $ — $ 982 U.S. government agency bonds 17,490 6 (54) 17,442 State and municipal bonds 10,924 10 — 10,934 Corporate bonds and notes 181,109 369 (152) 181,326 $ 210,502 $ 388 $ (206) $ 210,684 Fair Value Measurements at December 31, 2023 Amortized Cost Gross Unrealized Gross Unrealized Fair Value Commercial paper $ 35,218 $ 18 $ (10) $ 35,226 U.S. government agency bonds 27,602 56 (186) 27,472 State and municipal bonds 15,262 1 (48) 15,215 Corporate bonds and notes 200,401 515 (255) 200,661 $ 278,483 $ 590 $ (499) $ 278,574
Schedule of Investment Maturity	December 31, 2024 December 31, 2023 Amortized Cost Fair Value Amortized Cost Fair Value Due in one year or less $ 110,918 $ 111,170 $ 150,297 $ 149,934 Due after one year through five years 99,584 99,514 128,186 128,640 $ 210,502 $ 210,684 $ 278,483 $ 278,574

Fair Value Measurements (Tables

Fair Value Measurements (Tables)	12 Months Ended
	Dec. 31, 2024
Fair Value Disclosures [Abstract]
Schedule of Assets and Liabilities That Are Measured at Fair Value on a Recurring Basis	The fair value measurements of our financial assets at December 31, 2024 and 2023 are summarized as follows: Fair Value Measurements at December 31, 2024 Level I Level II Level III Total Cash and cash equivalents $ 9,227 $ — $ — $ 9,227 Restricted cash 665 — — 665 Held-to-maturity investments: Commercial paper — 982 — 982 U.S. government agency bonds — 17,442 — 17,442 State and municipal bonds — 10,934 — 10,934 Corporate bonds and notes — 181,326 — 181,326 $ 9,892 $ 210,684 $ — $ 220,576 Fair Value Measurements at December 31, 2023 Level I Level II Level III Total Cash and cash equivalents $ 12,881 $ — $ — $ 12,881 Restricted cash 8,583 — — 8,583 Held-to-maturity investments: Commercial paper — 35,226 — 35,226 U.S. government agency bonds — 27,472 — 27,472 State and municipal bonds — 15,215 — 15,215 Corporate bonds and notes — 200,661 — 200,661 $ 21,464 $ 278,574 $ — $ 300,038

Capital Structure (Tables)

Capital Structure (Tables)	12 Months Ended
	Dec. 31, 2024
Equity [Abstract]
Schedule of Common Stock Reserved	At December 31, 2024, the following shares of common stock were reserved for future issuance: Unexercised stock options outstanding under 2016 Equity Incentive Plan 188,229 Shares granted and unvested under 2020 Equity Incentive Plan 6,090,445 Authorized for future grant under 2024 Equity Incentive Plan 11,015,317 Authorized for future issuance under the Hyliion Holdings Corp. Employee Stock Purchase Plan 1,800,000 19,093,991

Share-Based Compensation (Table

Share-Based Compensation (Tables)	12 Months Ended
	Dec. 31, 2024
Share-Based Payment Arrangement [Abstract]
Schedule of Share Option Activity	Activity in the 2020 Plan for the years ended December 31, 2024 and 2023 is summarized as follows: Number of Units Weighted Average Grant Date Fair Value (in Dollars) Unvested at December 31, 2022 1 2,769,100 $ 5.51 Granted 2 2,192,900 2.57 Vested (1,350,172) 5.28 Forfeited 3 (860,505) 4.53 Unvested at December 31, 2023 4 2,751,323 3.59 Granted 5,878,591 1.05 Vested (1,267,658) 3.87 Forfeited (1,271,811) 2.61 Unvested at December 31, 2024 6,090,445 $ 1.28 1 Excludes 1,336,667 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. 2 Excludes 25,000 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. 3 Excludes 59,584 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. 4 Excludes 633,750 shares underlying RSU awards with performance conditions, which have not been accounted for because no accounting grant date has been established. These excluded shares were not granted during the year ended December 31, 2024. Activity in the 2016 Plan for the years ended December 31, 2024 and 2023 is summarized as follows: Number of Options Weighted Average Weighted Average Outstanding at December 31, 2022 2,541,439 $ 0.15 3.7 years Exercised (1,936,018) 0.13 Forfeited (82,450) 0.22 Outstanding at December 31, 2023 522,971 0.20 4.3 years Exercised (325,175) 0.21 Forfeited (9,567) 0.23 Outstanding at December 31, 2024 188,229 $ 0.20 4.7 years Exercisable at December 31, 2024 188,229 $ 0.20 4.7 years

Leases (Tables)

Leases (Tables)	12 Months Ended
	Dec. 31, 2024
Leases [Abstract]
Schedule of Operating Lease Costs and Finance Lease Costs	The following table provides a summary of the components of lease operating costs which are primarily included within R&D and selling, general and administrative expense: Year Ended December 31, 2024 2023 Operating lease costs: Operating lease cost $ 2,476 $ 2,239 Short-term lease cost 42 508 Variable lease cost 658 682 Total operating lease costs $ 3,176 $ 3,429
Schedule of Weighted-average Lease Terms and Discount Rates	The following table provides the weighted-average lease terms and discount rates used for the Company’s operating leases: December 31, 2024 2023 Weighted-average remaining lease term: Operating leases 2.6 years 3.6 years Weighted-average discount rate: Operating leases 8.6 % 8.7 %
Schedule of Lease Liability Maturities for the Next Five Years	The following table provides a summary of operating lease liability maturities for the next five years and thereafter at December 31, 2024: 2025 $ 2,900 2026 2,988 2027 1,426 2028 306 2029 — Thereafter — Total minimum lease payments 7,620 Less: imputed interest (828) Total lease obligations $ 6,792

Property and Equipment, Net (Ta

Property and Equipment, Net (Tables)	12 Months Ended
	Dec. 31, 2024
Property, Plant and Equipment [Abstract]
Schedule of Property and Equipment, Net	Property and equipment, net at December 31, 2024 and 2023 is summarized as follows: December 31, 2024 2023 Production machinery and equipment $ 27,846 $ 10,376 Vehicles 379 2,013 Leasehold improvements 4,313 2,236 Office furniture and fixtures 270 223 Computers and related equipment 2,113 1,963 34,921 16,811 Less: accumulated depreciation (9,001) (6,824) Total property and equipment, net $ 25,920 $ 9,987

Accrued Expenses and Other Cu_2

Accrued Expenses and Other Current Liabilities (Tables)	12 Months Ended
	Dec. 31, 2024
Accrued Liabilities and Other Liabilities [Abstract]
Schedule of Accrued Expenses and Other Current Liabilities	Accrued expenses and other current liabilities at December 31, 2024 and 2023 are summarized as follows: December 31, 2024 2023 Accrued professional services and other $ 1,823 $ 2,606 Accrued compensation and related benefits 3,280 1,510 Other accrued liabilities 746 1,922 Accrued severance, contract termination, and other charges 773 4,013 $ 6,622 $ 10,051

Income Taxes (Tables)

Income Taxes (Tables)	12 Months Ended
	Dec. 31, 2024
Income Tax Disclosure [Abstract]
Schedule of Provision for Income Taxes	The income tax provision for the years ended December 31, 2024 and 2023 is summarized as follows: Year Ended December 31, 2024 2023 Current tax expense: Federal $ — $ — State — — Total current tax expense $ — $ — Deferred tax (benefit) expense: Federal $ (10,493) $ (25,328) State — — Valuation allowance 10,493 25,328 Total deferred tax expense $ — $ —
Schedule of Deferred Taxes	The components of deferred taxes at December 31, 2024 and 2023 are summarized as follows: December 31, 2024 2023 Deferred tax assets: Federal net operating loss carryforwards $ 72,697 $ 62,561 State net operating loss carryforwards 491 491 Operating lease obligation 1,426 1,604 Section 174 expenditures 28,445 26,444 R&D tax credit 4,714 4,714 Other 1,676 3,235 Intangible assets, net 5,159 5,522 Total deferred tax assets 114,608 104,571 Less: valuation allowance (113,296) (102,803) Deferred tax assets, net of valuation allowance 1,312 1,768 Deferred tax liabilities: Operating lease right of use asset, net 1,140 1,485 Property and equipment, net 172 283 Total deferred tax liabilities 1,312 1,768 Net deferred tax assets $ — $ —
Schedule of Reconciliation of Taxes at Federal Statutory Rate to Provision for Income Taxes	The reconciliation of taxes at the federal statutory rate to the Company’s provision for income taxes for the years ended December 31, 2024 and 2023 is summarized as follows: Year Ended December 31, 2024 2023 Provision at statutory rate of 21% $ (10,930) $ (25,937) Other 437 609 Change in valuation allowance 10,493 25,328 $ — $ —

Net Loss Per Share (Tables)

Net Loss Per Share (Tables)	12 Months Ended
	Dec. 31, 2024
Earnings Per Share [Abstract]
Schedule of Basic and Diluted Net Loss Per Share	The computation of basic and diluted net loss per share for the years ended December 31, 2024 and 2023 is summarized as follows (in thousands, except share and per share data): Year Ended December 31, 2024 2023 Numerator: Net loss attributable to common stockholders $ (52,048) $ (123,510) Denominator: Weighted average shares outstanding, basic and diluted 174,915,487 181,411,069 Net loss per share, basic and diluted $ (0.30) $ (0.68)
Schedule of Potential Common Shares	Potential common shares excluded from the computation of diluted net loss per share because including them would have had an anti-dilutive effect for the years ended December 31, 2024 and 2023 are summarized as follows: Year Ended December 31, 2024 2023 Unexercised stock options 188,229 522,971 Unvested restricted stock units 6,322,621 3,385,073 6,510,850 3,908,044

Supplemental Cash Flow Inform_2

Supplemental Cash Flow Information (Tables)	12 Months Ended
	Dec. 31, 2024
Supplemental Cash Flow Elements [Abstract]
Schedule of Supplemental Cash Flow Information	Supplemental cash flow information for the years ended December 31, 2024 and 2023 is summarized as follows: Year Ended December 31, 2024 2023 Cash paid for interest $ — $ — Cash paid for taxes $ — $ — Cash paid for amounts included in the measurement of lease liabilities: Operating cash flows from operating leases, net $ (1,687) $ (2,470) Right-of-use assets obtained in exchange for lease obligations $ — $ 2,096
Schedule of Supplemental Disclosures of Noncash Financing Activities	Year Ended December 31, 2024 2023 Supplemental disclosure of noncash investing and financing activities: Repurchase of treasury stock included in accrued expenses and other current liabilities $ 117 $ — Acquisitions of property and equipment and intangible assets included in accounts payable and accrued expenses and other current liabilities $ 3,884 $ 292

Description of Organization a_2

Description of Organization and Business Operations and Basis of Presentation (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Total equity	$ 244,389	$ 306,266	$ 423,574
Cash and cash equivalents	9,227	$ 12,881	$ 119,468
Investments	$ 210,500

Disposals - Narrative (Details)

Disposals - Narrative (Details) - USD ($)	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Business Acquisition [Line Items]
Restructuring Charges, Statement of Income or Comprehensive Income [Extensible Enumeration]	Charged to Expense (Benefit)	Charged to Expense (Benefit)
Gain on disposal of assets	$ 3,000	$ 1,000
Strategic Plan
Business Acquisition [Line Items]
Charges and expenses incurred	3,000,000	11,500,000
Assets held for sale	2,600,000	0
Fair value charges	6,500,000	0
Gain on disposal of assets	$ 2,800,000	$ 0

Disposals - Schedule of Changes

Disposals - Schedule of Changes in Plan Liabilities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Restructuring Reserve [Roll Forward]
Charged to Expense (Benefit)	$ 3,007	$ 11,474
Strategic Plan
Restructuring Reserve [Roll Forward]
Beginning balance	8,000	500
Charged to Expense (Benefit)	(1,100)	9,500
Costs Paid or Settled	(6,100)	(2,000)
Ending balance	800	8,000
Strategic Plan | Employee severance and retention
Restructuring Reserve [Roll Forward]
Beginning balance	1,100	0
Charged to Expense (Benefit)	0	1,200
Costs Paid or Settled	(1,000)	(100)
Ending balance	100	1,100
Strategic Plan | Contract terminations
Restructuring Reserve [Roll Forward]
Beginning balance	6,500	0
Charged to Expense (Benefit)	(800)	8,200
Costs Paid or Settled	(5,100)	(1,700)
Ending balance	600	6,500
Strategic Plan | Warranty obligations
Restructuring Reserve [Roll Forward]
Beginning balance	400	500
Charged to Expense (Benefit)	(300)	100
Costs Paid or Settled	0	(200)
Ending balance	$ 100	$ 400

Summary of Significant Accoun_4

Summary of Significant Accounting Policies - Narrative (Details)	3 Months Ended	9 Months Ended	12 Months Ended
	Dec. 31, 2024 USD ($) renewal_option contract	Sep. 30, 2024 USD ($) contract	Dec. 31, 2024 USD ($) renewal_option generator	Dec. 31, 2023 USD ($)	Mar. 31, 2024 USD ($)	Dec. 31, 2021
Lessee, Lease, Description [Line Items]
Accounts receivable from customers	$ 1,500,000		$ 1,500,000	$ 0
Maturity date (or less)	36 months		36 months
Government assistance, number of contracts | contract	3	2
Received cash grants					$ 1,100,000
Options to renew (at least) | renewal_option	1		1
Lease extension	5 years		5 years			3 years
Marketing and advertising expense			$ 100,000	$ 1,300,000
Research and Development Service
Lessee, Lease, Description [Line Items]
Payment due (in days)	90 days		90 days
Government assistance, number of generators | generator			7
Supplier
Lessee, Lease, Description [Line Items]
Letter of credit	$ 7,900,000		$ 7,900,000
Corporate Headquarters Lessor
Lessee, Lease, Description [Line Items]
Letter of credit	$ 700,000		$ 700,000
Minimum
Lessee, Lease, Description [Line Items]
Lease extension	1 year		1 year
Maximum
Lessee, Lease, Description [Line Items]
Lease extension	5 years		5 years
Maximum | Research and Development Service
Lessee, Lease, Description [Line Items]
Received cash grants	$ 15,700,000	$ 16,000,000	$ 15,700,000

Summary of Significant Accoun_5

Summary of Significant Accounting Policies - Schedule of Significant Expense Categories (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Disaggregation of Revenue [Line Items]
Revenues	$ 1,509	$ 672
Cost of revenues	1,415	1,716
Gross profit (loss)	94	(1,044)
Depreciation and amortization	3,147	3,511
Product development, exclusive of other costs presented	37,004	82,240
Exit and termination costs	3,007	11,474
Total operating expenses	64,393	136,325
Net loss	(52,048)	(123,510)
Reportable Segment
Disaggregation of Revenue [Line Items]
Revenues	1,500	700
Cost of revenues	1,400	1,700
Gross profit (loss)	100	(1,000)
Administrative and office	7,700	12,400
Depreciation and amortization	3,100	2,400
Facilities	5,100	5,000
Personnel	24,300	46,700
Product development, exclusive of other costs presented	15,000	34,000
Professional services	5,200	21,700
Exit and termination costs	3,000	11,500
Other operating expense	1,000	2,600
Total operating expenses	64,400	136,300
Other income, net	12,300	13,800
Net loss	$ (52,000)	$ (123,500)

Summary of Significant Accoun_6

Summary of Significant Accounting Policies - Restricted Cash (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Accounting Policies [Abstract]
Cash and cash equivalents	$ 9,227	$ 12,881	$ 119,468
Restricted cash included in prepaid expenses and other current assets	0	7,918	0
Restricted cash included in other assets	665	665	665
Total cash and cash equivalents	$ 9,892	$ 21,464	$ 120,133

Summary of Significant Accoun_7

Summary of Significant Accounting Policies - Schedule of Estimated Useful Lives (Details)	Dec. 31, 2024
Production machinery and equipment | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	2 years
Production machinery and equipment | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	12 years
Vehicles | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Vehicles | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Leasehold improvements
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	7 years
Furniture and fixtures
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Computers and related equipment | Minimum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	3 years
Computers and related equipment | Maximum
Public Utility, Property, Plant and Equipment [Line Items]
Estimated useful life	7 years

Summary of Significant Accoun_8

Summary of Significant Accounting Policies - Schedule of Significant Customers (Details) - Revenues - Significant Customers	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Customer A
Disaggregation of Revenue [Line Items]
Concentration risk	88%	0%
Customer B
Disaggregation of Revenue [Line Items]
Concentration risk	12%	0%
Customer C
Disaggregation of Revenue [Line Items]
Concentration risk	0%	65%
Customer D
Disaggregation of Revenue [Line Items]
Concentration risk	0%	25%
Customers
Disaggregation of Revenue [Line Items]
Concentration risk	100%	90%

Investments - Schedule of Amort

Investments - Schedule of Amortized Cost, Unrealized Gains and Losses, and Fair Value (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Held-to-maturity investments
Amortized Cost	$ 210,502	$ 278,483
Gross Unrealized Gains	388	590
Gross Unrealized Losses	(206)	(499)
Fair Value	210,684	278,574
Commercial paper
Held-to-maturity investments
Amortized Cost	979	35,218
Gross Unrealized Gains	3	18
Gross Unrealized Losses	0	(10)
Fair Value	982	35,226
U.S. government agency bonds
Held-to-maturity investments
Amortized Cost	17,490	27,602
Gross Unrealized Gains	6	56
Gross Unrealized Losses	(54)	(186)
Fair Value	17,442	27,472
State and municipal bonds
Held-to-maturity investments
Amortized Cost	10,924	15,262
Gross Unrealized Gains	10	1
Gross Unrealized Losses	0	(48)
Fair Value	10,934	15,215
Corporate bonds and notes
Held-to-maturity investments
Amortized Cost	181,109	200,401
Gross Unrealized Gains	369	515
Gross Unrealized Losses	(152)	(255)
Fair Value	$ 181,326	$ 200,661

Investments - Schedule of Inves

Investments - Schedule of Investment Maturity (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Amortized Cost
Due in one year or less	$ 110,918	$ 150,297
Due after one year through five years	99,584	128,186
Amortized cost	210,502	278,483
Fair Value
Due in one year or less	111,170	149,934
Due after one year through five years	99,514	128,640
Fair Value, Total held-to-maturity securities	$ 210,684	$ 278,574

Fair Value Measurements - Sched

Fair Value Measurements - Schedule of Assets and Liabilities That Are Measured at Fair Value on a Recurring Basis (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	$ 9,227	$ 12,881
Restricted cash	665	8,583
Held-to-maturity investments:	210,684	278,574
Total assets	220,576	300,038
Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	982	35,226
U.S. government agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	17,442	27,472
State and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	10,934	15,215
Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	181,326	200,661
Level I
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	9,227	12,881
Restricted cash	665	8,583
Total assets	9,892	21,464
Level I | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level I | U.S. government agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level I | State and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level I | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level II
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash	0	0
Total assets	210,684	278,574
Level II | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	982	35,226
Level II | U.S. government agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	17,442	27,472
Level II | State and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	10,934	15,215
Level II | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	181,326	200,661
Level III
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Cash and cash equivalents	0	0
Restricted cash	0	0
Total assets	0	0
Level III | Commercial paper
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level III | U.S. government agency bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level III | State and municipal bonds
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	0	0
Level III | Corporate bonds and notes
Fair Value, Assets and Liabilities Measured on Recurring and Nonrecurring Basis [Line Items]
Held-to-maturity investments:	$ 0	$ 0

Capital Structure - Narrative (

Capital Structure - Narrative (Details) - USD ($)	Dec. 31, 2024	Dec. 31, 2023
Equity [Abstract]
Preferred stock, shares authorized	10,000,000
Preferred stock, par value (in dollars per share)	$ 0.0001
Preferred stock, shares issued (in shares)	0	0
Preferred stock outstanding (in shares)	0	0
Share repurchase authorized		$ 20,000,000

Capital Structure - Schedule of

Capital Structure - Schedule of Common Stock Reserved (Details)	Dec. 31, 2024 shares
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Unexercised stock options outstanding under 2016 Equity Incentive Plan	188,229
Shares granted and unvested under 2020 Equity Incentive Plan	6,090,445
Total	19,093,991
Authorized for future grant under 2024 Equity Incentive Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Authorized for future grant and issuance	11,015,317
Authorized for future issuance under the Hyliion Holdings Corp. Employee Stock Purchase Plan
Share-Based Compensation Arrangement by Share-Based Payment Award [Line Items]
Authorized for future grant and issuance	1,800,000

Share-Based Compensation - Narr

Share-Based Compensation - Narrative (Details)	12 Months Ended
	Dec. 31, 2024 USD ($) $ / shares shares	Dec. 31, 2023 USD ($)	May 21, 2024 shares	Oct. 01, 2020 shares
Share-based Compensation (Details) [Line Items]
Employee and nonemployee award vesting period	4 years
Maximum term	10 years
Options outstanding intrinsic value	$ 500,000
Exercisable intrinsic value	300,000
Intrinsic value of options exercised	$ 400,000	$ 2,400,000
RSUs
Share-based Compensation (Details) [Line Items]
Awards granted (in shares) | shares	2,700,000
Closing stock price percentage	1
Grants intrinsic value, amount (in USD per share) | $ / shares	$ 0.83
Volatility rate	90%
Risk free interest rate	4.35%
Employee Stock
Share-based Compensation (Details) [Line Items]
Contribution percent of base compensation	15%
Purchase percent of market value	85%
2016 Equity Incentive Plan
Share-based Compensation (Details) [Line Items]
Authorized for granted (in shares) | shares	0
Share-based compensation expense	$ 0
Unrecognized compensation cost related to share-based payments	$ 0
Weighted average remaining contractual term, exercisable	4 years 8 months 12 days
2020 Equity Incentive Plan
Share-based Compensation (Details) [Line Items]
Authorized for granted (in shares) | shares				12,200,000
Share-based compensation expense	$ 4,600,000	6,200,000
Unrecognized compensation cost related to share-based payments	$ 4,600,000
Weighted average remaining contractual term, exercisable	1 year 9 months 18 days
2020 Equity Incentive Plan | RSUs
Share-based Compensation (Details) [Line Items]
Fair value of RSUs that vested in period	$ 2,300,000	2,800,000
2020 Equity Incentive Plan | RSUs | Minimum
Share-based Compensation (Details) [Line Items]
Employee and nonemployee award vesting period	1 year
2020 Equity Incentive Plan | RSUs | Maximum
Share-based Compensation (Details) [Line Items]
Employee and nonemployee award vesting period	3 years
2024 Equity Incentive Plan
Share-based Compensation (Details) [Line Items]
Authorized for granted (in shares) | shares			8,000,000
Share-based compensation expense	$ 0	0
Unrecognized compensation cost related to share-based payments	$ 400,000
Weighted average remaining contractual term, exercisable	2 years 8 months 12 days
2024 Equity Incentive Plan | RSUs
Share-based Compensation (Details) [Line Items]
Fair value of RSUs that vested in period	$ 0	$ 0

Share-Based Compensation - Sche

Share-Based Compensation - Schedule of Share Option Activity 2024 (Details)	12 Months Ended
	Dec. 31, 2024 $ / shares shares
Number of Options
Shares, Balance at end (in shares)	188,229
2024 Equity Incentive Plan
Number of Options
Shares, Balance at beginning (in shares)	0
Granted (in shares)	232,176
Shares, Balance at end (in shares)	232,176
Weighted Average Exercise Price (in Dollars)
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 0
Granted (in dollars per share) | $ / shares	1.81
Weighted average grant date fair value (in dollars per share) | $ / shares	$ 1.81

Share-Based Compensation - Sc_2

Share-Based Compensation - Schedule of Share Option Activity 2020 (Details) - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Number of Options
Shares, Balance at end (in shares)	188,229
2020 Equity Incentive Plan
Number of Options
Shares, Balance at beginning (in shares)	2,751,323	2,769,100
Granted (in shares)	5,878,591	2,192,900
Vested (in shares)	(1,267,658)	(1,350,172)
Forfeited (in shares)	(1,271,811)	(860,505)
Shares, Balance at end (in shares)	6,090,445	2,751,323
Weighted Average Exercise Price (in Dollars)
Weighted average grant date fair value (in dollars per share)	$ 3.59	$ 5.51
Granted (in dollars per share)	1.05	2.57
Vested (in dollars per share)	3.87	5.28
Forfeited (in dollars per share)	2.61	4.53
Weighted average grant date fair value (in dollars per share)	$ 1.28	$ 3.59
Forfeited (in shares)	1,271,811	860,505
2020 Equity Incentive Plan | No established accounting grant date
Number of Options
Shares, Balance at beginning (in shares)	633,750	1,336,667
Granted (in shares)		25,000
Forfeited (in shares)		(59,584)
Shares, Balance at end (in shares)		633,750
Weighted Average Exercise Price (in Dollars)
Forfeited (in shares)		59,584

Share-Based Compensation - Sc_3

Share-Based Compensation - Schedule of Share Option Activity 2016 (Details) - $ / shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023	Dec. 31, 2022
Number of Options
Shares, Balance at end (in shares)	188,229
2016 Equity Incentive Plan
Number of Options
Shares, Balance at beginning (in shares)	522,971	2,541,439
Exercised (in shares)	(325,175)	(1,936,018)
Forfeited (in shares)	(9,567)	(82,450)
Shares, Balance at end (in shares)	188,229	522,971	2,541,439
Shares, Exercisable	188,229
Weighted Average Exercise Price (in Dollars)
Weighted average grant date fair value (in dollars per share)	$ 0.20	$ 0.15
Exercised (in dollars per share)	0.21	0.13
Forfeited (in dollars per share)	0.23	0.22
Weighted average grant date fair value (in dollars per share)	0.20	$ 0.20	$ 0.15
Weighted Average Exercise Price, Exercisable (in dollars per share)	$ 0.20
Weighted Average Remaining Contractual Term
Weighted Average Remaining Contractual Term, Balance			3 years 8 months 12 days
Weighted Average Remaining Contractual Term, Balance	4 years 8 months 12 days	4 years 3 months 18 days
Weighted average remaining contractual term, exercisable	4 years 8 months 12 days

Leases - Narrative (Details)

Leases - Narrative (Details) - extension	Dec. 31, 2024	Dec. 31, 2021
Leases [Abstract]
Number of consecutive term extensions	2	2
Lease extension	5 years	3 years

Leases - Schedule of Operating

Leases - Schedule of Operating Lease Costs and Finance Lease Costs (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Operating lease costs:
Operating lease cost	$ 2,476	$ 2,239
Short-term lease cost	42	508
Variable lease cost	658	682
Total operating lease costs	$ 3,176	$ 3,429

Leases - Schedule of Weighted-a

Leases - Schedule of Weighted-average Lease Terms and Discount Rates (Details)	Dec. 31, 2024	Dec. 31, 2023
Weighted-average remaining lease term:
Operating leases	2 years 7 months 6 days	3 years 7 months 6 days
Weighted-average discount rate:
Operating leases	8.60%	8.70%

Leases - Schedule of Lease Liab

Leases - Schedule of Lease Liability Maturities for the Next Five Years (Details) $ in Thousands	Dec. 31, 2024 USD ($)
Operating Leases
2025	$ 2,900
2026	2,988
2027	1,426
2028	306
2029	0
Thereafter	0
Total minimum lease payments	7,620
Less: imputed interest	(828)
Total lease obligations	$ 6,792

Property and Equipment, Net - S

Property and Equipment, Net - Schedule of Property and Equipment, Net (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 34,921	$ 16,811
Less: accumulated depreciation	(9,001)	(6,824)
Total property and equipment, net	25,920	9,987
Production machinery and equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	27,846	10,376
Vehicles
Property, Plant and Equipment [Line Items]
Property and equipment, gross	379	2,013
Leasehold improvements
Property, Plant and Equipment [Line Items]
Property and equipment, gross	4,313	2,236
Office furniture and fixtures
Property, Plant and Equipment [Line Items]
Property and equipment, gross	270	223
Computers and related equipment
Property, Plant and Equipment [Line Items]
Property and equipment, gross	$ 2,113	$ 1,963

Property and Equipment, Net - N

Property and Equipment, Net - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 3.1	$ 3.2
Selling, General and Administrative Expenses
Property, Plant and Equipment [Line Items]
Depreciation expense	0.4	0.6
Research and Development Expense
Property, Plant and Equipment [Line Items]
Depreciation expense	$ 2.7	1.7
Exit And Termination Costs
Property, Plant and Equipment [Line Items]
Depreciation expense		$ 0.9

Accrued Expenses and Other Cu_3

Accrued Expenses and Other Current Liabilities - Schedule of accrued expenses and other current liabilities (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Accrued Liabilities and Other Liabilities [Abstract]
Accrued professional services and other	$ 1,823	$ 2,606
Accrued compensation and related benefits	3,280	1,510
Other accrued liabilities	746	1,922
Accrued severance, contract termination, and other charges	773	4,013
Total	$ 6,622	$ 10,051

Income Taxes - Schedule of Prov

Income Taxes - Schedule of Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Current tax expense:
Federal	$ 0	$ 0
State	0	0
Total current tax expense	0	0
Deferred tax (benefit) expense:
Federal	(10,493)	(25,328)
State	0	0
Valuation allowance	10,493	25,328
Total deferred tax expense	$ 0	$ 0

Income Taxes - Schedule of Defe

Income Taxes - Schedule of Deferred Taxes (Details) - USD ($) $ in Thousands	Dec. 31, 2024	Dec. 31, 2023
Deferred tax assets:
Federal net operating loss carryforwards	$ 72,697	$ 62,561
State net operating loss carryforwards	491	491
Operating lease obligation	1,426	1,604
Section 174 expenditures	28,445	26,444
R&D tax credit	4,714	4,714
Other	1,676	3,235
Intangible assets, net	5,159	5,522
Total deferred tax assets	114,608	104,571
Less: valuation allowance	(113,296)	(102,803)
Deferred tax assets, net of valuation allowance	1,312	1,768
Deferred tax liabilities:
Operating lease right of use asset, net	1,140	1,485
Property and equipment, net	172	283
Total deferred tax liabilities	1,312	1,768
Net deferred tax assets	$ 0	$ 0

Income Taxes - Schedule of Reco

Income Taxes - Schedule of Reconciliation of Taxes at Federal Statutory Rate to Provision for Income Taxes (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Tax Disclosure [Abstract]
Provision at statutory rate of 21%	$ (10,930)	$ (25,937)
Other	437	609
Change in valuation allowance	10,493	25,328
Total	$ 0	$ 0

Income Taxes - Narrative (Detai

Income Taxes - Narrative (Details) - USD ($) $ in Millions	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Income Taxes [Line Items]
R&D tax credit	$ 0.1
Net operating loss	2
2037
Income Taxes [Line Items]
R&D tax credit	4.7
Federal
Income Taxes [Line Items]
Net operating loss carryforwards	346.2	$ 297.9
Federal | 2036
Income Taxes [Line Items]
Net operating loss carryforwards	10.5
Federal | Indefinite
Income Taxes [Line Items]
Net operating loss carryforwards	335.7
State and Local Jurisdiction
Income Taxes [Line Items]
Net operating loss carryforwards	$ 12.5	$ 12.5

Commitments and Contingencies (

Commitments and Contingencies (Details) - USD ($) $ in Millions	Dec. 31, 2024	Mar. 31, 2024
Commitments and Contingencies Disclosure [Abstract]
Received cash grants		$ 1.1
Refundable payments received	$ 0.4
Government Assistance, Liability, Noncurrent, Statement of Financial Position [Extensible Enumeration]	Accrued expenses and other current liabilities

Net Loss Per Share - Schedule o

Net Loss Per Share - Schedule of Basic and Diluted Net Loss Per Share (Details) - USD ($) $ / shares in Units, $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Numerator:
Net loss attributable to common stockholders	$ (52,048)	$ (123,510)
Denominator:
Weighted-average shares outstanding, basic (in shares)	174,915,487	181,411,069
Weighted-average shares outstanding, diluted (in shares)	174,915,487	181,411,069
Net loss per share, basic (in dollars per share)	$ (0.30)	$ (0.68)
Net loss per share, diluted (in dollars per share)	$ (0.30)	$ (0.68)

Net Loss Per Share - Schedule_2

Net Loss Per Share - Schedule of Potential Common Shares (Details) - shares	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common shares excluded from computation of diluted Net (loss) income per share	6,510,850	3,908,044
Unexercised stock options
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common shares excluded from computation of diluted Net (loss) income per share	188,229	522,971
Unvested restricted stock units
Antidilutive Securities Excluded from Computation of Earnings Per Share [Line Items]
Common shares excluded from computation of diluted Net (loss) income per share	6,322,621	3,385,073

Supplemental Cash Flow Inform_3

Supplemental Cash Flow Information - Schedule of Supplemental Cash Flow Information (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Supplemental Cash Flow Elements [Abstract]
Cash paid for interest	$ 0	$ 0
Cash paid for taxes	0	0
Cash paid for amounts included in the measurement of lease liabilities:
Operating cash flows from operating leases, net	(1,687)	(2,470)
Right-of-use assets obtained in exchange for lease obligations	$ 0	$ 2,096

Supplemental Cash Flow Inform_4

Supplemental Cash Flow Information - Schedule of Supplemental Disclosures of Noncash Financing Activities (Details) - USD ($) $ in Thousands	12 Months Ended
	Dec. 31, 2024	Dec. 31, 2023
Supplemental Cash Flow Elements [Abstract]
Repurchase of treasury stock included in accrued expenses and other current liabilities	$ 117	$ 0
Acquisitions of property and equipment and intangible assets included in accounts payable and accrued expenses and other current liabilities	$ 3,884	$ 292

Retirement Plan (Details)

Retirement Plan (Details)	12 Months Ended
	Dec. 31, 2024
Retirement Benefits [Abstract]
Participants minimum required age limit of plan	21 years