SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)	6 Months Ended
Jun. 30, 2024
Accounting Policies [Abstract]
Principles of Consolidation	The accompanying unaudited condensed consolidated financial statements represent the historical operations of the standalone GRAIL legal entity and include purchase accounting adjustments and certain tax adjustments as if the Company filed a separate income tax return and was not included in Illumina’s consolidated return for the period of time the Company was owned by Illumina. All revenues and costs as well as assets and liabilities directly associated with the business activity of the Company are included in the unaudited condensed consolidated financial statements. Certain assets and liabilities were reflected at fair value under the new basis of accounting established at the closing of Illumina’s acquisition of the Company in August 2021 (“the Acquisition”). Management considered the need to allocate any historical shared costs incurred by the parent, Illumina, to the accompanying condensed consolidated financial statements. As previously discussed, the European Commission adopted an order requiring Illumina and GRAIL to be held and operated as distinct and separate entities. As no integration ever occurred, management concluded that no material allocations were required. As of December 31, 2023, the Company had generated net operating loss carryforwards for federal and state tax purposes of $3.5 billion and $2.3 billion, respectively. As a single member LLC disregarded for tax purposes, these tax attributes are the sole property of Illumina and remained the assets of Illumina following the Spin-off in accordance with the Internal Revenue Code. However, amounts recognized by the Company are not necessarily representative of the amounts that would have been reflected in the financial statements had the Company operated independently of the parent. Related party transactions with Illumina are discussed further in Note 6 — Related Party Transactions.
Basis of Presentation	These unaudited condensed consolidated financial statements are prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”), reflect all normal recurring adjustments that are necessary to present the results fairly, and include the accounts of the Company and its wholly owned subsidiaries for the interim periods presented. All intercompany balances have been eliminated in consolidation.
Stock-Based Compensation Expense	Stock-Based Compensation Expense The Company’s stock-based compensation expense includes expenses related to cash-based equity incentive awards, restricted stock units (“RSUs”), and performance stock options. Forfeitures are accounted for as incurred. In connection with the Spin-Off, GRAIL and Illumina entered into an Employee Matters Agreement pursuant to which the Company’s equity awards were modified (the “Award Modification”). A cash-based equity incentive award (the “Cash-Based Equity Award”) program was adopted following Illumina’s acquisition of GRAIL in 2021 to provide GRAIL employees with dollar-denominated long-term incentive awards. The cash-settled, liability-classified awards were modified to become RSUs that will be settled in shares of the Company’s common stock upon vesting. Unvested performance stock options that were previously held by certain GRAIL employees to purchase Illumina common stock were also converted to options to purchase GRAIL common stock in connection with the Spin-Off. See Note 5 — Stock-Based Compensation for further details of the Award Modification. Prior to the Award Modification, the Cash-Based Equity Awards were liability-classified awards because the Cash-Based Equity Awards could be settled in cash. Until April 30, 2024, GRAIL’s stand-alone value calculation was estimated by the Company based on its analysis and the input from independent valuation advisors. The value of the Cash-Based Equity Awards was recorded over the applicable vesting periods, with recognition of a corresponding liability recorded in incentive plan liabilities in the consolidated balance sheets. The Cash-Based Equity Awards were remeasured at each reporting date until settlement with changes in fair value recognized in stock-based compensation expense. On April 30, 2024, Illumina’s Compensation Committee approved an adjustment of the ordinary course payouts of the Cash-Based Equity Awards providing that the Cash-Based Equity Awards would be paid based on their nominal (face) value without adjustment based on changes in equity value. Subsequent to this adjustment to the Cash-Based Equity Awards and continuing until the Award Modification, the Cash-Based Equity Awards were expensed in accordance with their applicable vesting schedules. The grant date fair value of RSUs are determined based on the closing market price of GRAIL’s common stock on the date of the grant (in the case of RSUs resulting from the Award Modification, the date of the Award Modification). Stock-based compensation expense is recognized based on the fair value on a straight-line basis over the requisite service periods of the RSUs. The fair value of performance stock options with service conditions is determined using the Black-Scholes-Merton option-pricing model. The model assumptions include expected volatility, term, dividends, and the risk-free interest rate. The expected volatility is generally determined by weighing the historical and implied volatility of peer companies’ common stock. The expected term is the Company’s best estimates based on the vesting period and contractual term. Given that cash dividends were never declared or paid on the Illumina nor GRAIL common stock, the expected dividend yield is determined to be 0%. The Company does not anticipate paying cash dividends in the foreseeable future. The risk-free interest rate is based upon U.S. Treasury securities with remaining terms similar to the expected term of the stock-based awards. The fair value of the performance stock options begins to be recognized when it is probable that the performance-based condition will be met.
Provision for (Benefit from) Income Taxes	Provision for (Benefit from) Income Taxes As a standalone entity, the Company files tax returns on its own behalf, and tax balances and the effective income tax rate may differ from the amounts reported in historical periods. As of June 24, 2024 and in connection with the Spin-Off, the Company adjusted its deferred tax balances and computed its related tax provision to reflect operations as a standalone entity. During the period that Illumina held the Company, the Company’s activity generated various tax attributes recognized as deferred tax assets (“DTAs”), due primarily to the generation of net operating losses (“NOLs”), IRC 174 capitalized research and experimental expenditures, and research and development (“R&D”) tax credits that could not be specifically utilized by the Company as it did not generate positive taxable income and it was not a separately regarded tax paying entity from Illumina. Since the Company was not a separately regarded taxable entity from Illumina, these tax attributes were either utilized by or will be utilized by Illumina when filing its consolidated tax return. Historically, the tax attributes were only presented in the Company’s stand-alone financial statements to allow the users to understand the financial position of the Company as a stand-alone taxable entity under the Separate-Return Method. The total tax-effected value of the tax attributes, net of Financial Accounting Standards Board Interpretation No. 48 (“FIN48”) liabilities and valuation allowance that were deemed to be the property of Illumina, was $447.2 million. In connection with the Spin-off, the underlying $447.2 million of tax attributes were adjusted through an entry of $447.2 million to additional paid in capital.
Net Loss Per Share Attributable to Common Stockholders	Net Loss Per Share Attributable to Common Stockholders The Company calculates basic net loss per share attributable to common stockholders by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed based on the sum of the weighted average number of common shares and potentially dilutive common shares outstanding during the period. In loss periods, basic and diluted net loss per share are identical since the effect of potentially dilutive common shares is antidilutive and therefore excluded. Potentially dilutive common shares consist of shares issuable under equity awards. Potentially dilutive common shares from equity awards are determined using the average share price for each period under the treasury stock method. In addition, proceeds from exercise of equity awards and the average amount of unrecognized compensation expense for equity awards are assumed to be used to repurchase shares.
Cash Equivalents	Cash Equivalents As of June 30, 2024 and December 31, 2023, the Company’s cash equivalents were held in money market funds, totaling $955.9 million and $92.6 million, respectively. In connection with the consummation of the Spin-Off, in June 2024, Illumina provided disposal funding of $932.3 million to the Company in accordance with the Separation and Distribution Agreement. Cash equivalents held in money market funds were categorized as Level 1 investments within the fair value hierarchy. Except for the accounting policies described above, there were no changes to the Company’s significant accounting policies during the three months ended June 30, 2024 as described in Note 2 — Summary of Significant Accounting Policies to the Company’s audited Consolidated Financial Statements filed with its Form 10 Registration Statement on June 3, 2024.
Recently Adopted Accounting Pronouncements and Accounting Pronouncements Not Yet Adopted	Recently Adopted Accounting Pronouncements The Company evaluates all Accounting Standards Updates (“ASUs”) issued by the Financial Accounting Standards Board (the "FASB") for consideration of their applicability. ASUs not included in the disclosures in this report were assessed and determined to be either not applicable or are not expected to have a material impact on the Company’s condensed consolidated financial statements. Accounting Pronouncements Not Yet Adopted In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This update improves reportable segment disclosure requirements, primarily through enhanced disclosures of significant segment expenses. This guidance will be effective for the annual reporting periods beginning the year ended December 31, 2024, and for interim reporting periods beginning January 1, 2025, with early adoption permitted, and should be applied retrospectively. The Company is currently evaluating the potential impact of this guidance on its condensed consolidated financial statements. In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvement to Income Tax Disclosures. This update improves income tax disclosure requirements, primarily through enhanced transparency and decision usefulness of disclosures. This guidance will be effective for annual reporting periods beginning the year ended December 31, 2025, with early adoption permitted and can be applied on either a prospective or retroactive basis. The Company is currently evaluating the potential impact of this guidance on its condensed consolidated financial statements.

SUMMARY OF SIGNIFICANT ACCOUNTING POLICIES (Policies)

6 Months Ended

Jun. 30, 2024

The accompanying unaudited condensed consolidated financial statements represent the historical operations of the standalone GRAIL legal entity and include purchase accounting adjustments and certain tax adjustments as if the Company filed a separate income tax return and was not included in Illumina’s consolidated return for the period of time the Company was owned by Illumina. All revenues and costs as well as assets and liabilities directly associated with the business activity of the Company are included in the unaudited condensed consolidated financial statements. Certain assets and liabilities were reflected at fair value under the new basis of accounting established at the closing of Illumina’s acquisition of the Company in August 2021 (“the Acquisition”).

Management considered the need to allocate any historical shared costs incurred by the parent, Illumina, to the accompanying condensed consolidated financial statements. As previously discussed, the European Commission adopted an order requiring Illumina and GRAIL to be held and operated as distinct and separate entities. As no integration ever occurred, management concluded that no material allocations were required. As of December 31, 2023, the Company had generated net operating loss carryforwards for federal and state tax purposes of $3.5 billion and $2.3 billion, respectively. As a single member LLC disregarded for tax purposes, these tax attributes are the sole property of Illumina and remained the assets of Illumina following the Spin-off in accordance with the Internal Revenue Code. However, amounts recognized by the Company are not necessarily representative of the amounts that would have been reflected in the financial statements had the Company

operated independently of the parent. Related party transactions with Illumina are discussed further in Note 6 — Related Party Transactions.

Basis of Presentation

These unaudited condensed consolidated financial statements are prepared in accordance with United States Generally Accepted Accounting Principles (“U.S. GAAP”), reflect all normal recurring adjustments that are necessary to present the results fairly, and include the accounts of the Company and its wholly owned subsidiaries for the interim periods presented. All intercompany balances have been eliminated in consolidation.

Stock-Based Compensation Expense

The Company’s stock-based compensation expense includes expenses related to cash-based equity incentive awards, restricted stock units (“RSUs”), and performance stock options. Forfeitures are accounted for as incurred.

In connection with the Spin-Off, GRAIL and Illumina entered into an Employee Matters Agreement pursuant to which the Company’s equity awards were modified (the “Award Modification”). A cash-based equity incentive award (the “Cash-Based Equity Award”) program was adopted following Illumina’s acquisition of GRAIL in 2021 to provide GRAIL employees with dollar-denominated long-term incentive awards. The cash-settled, liability-classified awards were modified to become RSUs that will be settled in shares of the Company’s common stock upon vesting. Unvested performance stock options that were previously held by certain GRAIL employees to purchase Illumina common stock were also converted to options to purchase GRAIL common stock in connection with the Spin-Off. See Note 5 — Stock-Based Compensation for further details of the Award Modification.

Prior to the Award Modification, the Cash-Based Equity Awards were liability-classified awards because the Cash-Based Equity Awards could be settled in cash. Until April 30, 2024, GRAIL’s stand-alone value calculation was estimated by the Company based on its analysis and the input from independent valuation advisors. The value of the Cash-Based Equity Awards was recorded over the applicable vesting periods, with recognition of a corresponding liability recorded in incentive plan liabilities in the consolidated balance sheets. The Cash-Based Equity Awards were remeasured at each reporting date until settlement with changes in fair value recognized in stock-based compensation expense. On April 30, 2024, Illumina’s Compensation Committee approved an adjustment of the ordinary course payouts of the Cash-Based Equity Awards providing that the Cash-Based Equity Awards would be paid based on their nominal (face) value without adjustment based on changes in equity value. Subsequent to this adjustment to the Cash-Based Equity Awards and continuing until the Award Modification, the Cash-Based Equity Awards were expensed in accordance with their applicable vesting schedules.

The grant date fair value of RSUs are determined based on the closing market price of GRAIL’s common stock on the date of the grant (in the case of RSUs resulting from the Award Modification, the date of the Award Modification). Stock-based compensation expense is recognized based on the fair value on a straight-line basis over the requisite service periods of the RSUs.

The fair value of performance stock options with service conditions is determined using the Black-Scholes-Merton option-pricing model. The model assumptions include expected volatility, term, dividends, and the risk-free interest rate. The expected volatility is generally determined by weighing the historical and implied volatility of peer companies’ common stock. The expected term is the Company’s best estimates based on the vesting period and contractual term. Given that cash dividends were never declared or paid on the Illumina nor GRAIL common stock, the expected dividend yield is determined to be 0%. The Company does not anticipate paying cash dividends in the foreseeable future. The risk-free interest rate is based upon U.S. Treasury securities with

remaining terms similar to the expected term of the stock-based awards. The fair value of the performance stock options begins to be recognized when it is probable that the performance-based condition will be met.

Provision for (Benefit from) Income Taxes

As a standalone entity, the Company files tax returns on its own behalf, and tax balances and the effective income tax rate may differ from the amounts reported in historical periods. As of June 24, 2024 and in connection with the Spin-Off, the Company adjusted its deferred tax balances and computed its related tax provision to reflect operations as a standalone entity. During the period that Illumina held the Company, the Company’s activity generated various tax attributes recognized as deferred tax assets (“DTAs”), due primarily to the generation of net operating losses (“NOLs”), IRC 174 capitalized research and experimental expenditures, and research and development (“R&D”) tax credits that could not be specifically utilized by the Company as it did not generate positive taxable income and it was not a separately regarded tax paying entity from Illumina. Since the Company was not a separately regarded taxable entity from Illumina, these tax attributes were either utilized by or will be utilized by Illumina when filing its consolidated tax return. Historically, the tax attributes were only presented in the Company’s stand-alone financial statements to allow the users to understand the financial position of the Company as a stand-alone taxable entity under the Separate-Return Method. The total tax-effected value of the tax attributes, net of Financial Accounting Standards Board Interpretation No. 48 (“FIN48”) liabilities and valuation allowance that were deemed to be the property of Illumina, was $447.2 million. In connection with the Spin-off, the underlying $447.2 million of tax attributes were adjusted through an entry of $447.2 million to additional paid in capital.

Net Loss Per Share Attributable to Common Stockholders

The Company calculates basic net loss per share attributable to common stockholders by dividing the net loss attributable to common stockholders by the weighted-average number of shares of common stock outstanding for the period. Diluted net loss per share is computed based on the sum of the weighted average number of common shares and potentially dilutive common shares outstanding during the period. In loss periods, basic and diluted net loss per share are identical since the effect of potentially dilutive common shares is antidilutive and therefore excluded. Potentially dilutive common shares consist of shares issuable under equity awards. Potentially dilutive common shares from equity awards are determined using the average share price for each period under the treasury stock method. In addition, proceeds from exercise of equity awards and the average amount of unrecognized compensation expense for equity awards are assumed to be used to repurchase shares.

Cash Equivalents

As of June 30, 2024 and December 31, 2023, the Company’s cash equivalents were held in money market funds, totaling $955.9 million and $92.6 million, respectively. In connection with the consummation of the Spin-Off, in June 2024, Illumina provided disposal funding of $932.3 million to the Company in accordance with the Separation and Distribution Agreement. Cash equivalents held in money market funds were categorized as Level 1 investments within the fair value hierarchy.

Except for the accounting policies described above, there were no changes to the Company’s significant accounting policies during the three months ended June 30, 2024 as described in Note 2 — Summary of Significant Accounting Policies to the Company’s audited Consolidated Financial Statements filed with its Form 10 Registration Statement on June 3, 2024.

Recently Adopted Accounting Pronouncements and Accounting Pronouncements Not Yet Adopted

Recently Adopted Accounting Pronouncements

The Company evaluates all Accounting Standards Updates (“ASUs”) issued by the Financial Accounting Standards Board (the "FASB") for consideration of their applicability. ASUs not included in the disclosures in this report were assessed and determined to be either not applicable or are not expected to have a material impact on the Company’s condensed consolidated financial statements.

Accounting Pronouncements Not Yet Adopted

In November 2023, the FASB issued ASU No. 2023-07, Segment Reporting (Topic 280): Improvements to Reportable Segment Disclosures. This update improves reportable segment disclosure requirements, primarily through enhanced disclosures of significant segment expenses. This guidance will be effective for the annual reporting periods beginning the year ended December 31, 2024, and for interim reporting periods beginning January 1, 2025, with early adoption permitted, and should be applied retrospectively. The Company is currently evaluating the potential impact of this guidance on its condensed consolidated financial statements.

In December 2023, the FASB issued ASU No. 2023-09, Income Taxes (Topic 740): Improvement to Income Tax Disclosures. This update improves income tax disclosure requirements, primarily through enhanced transparency and decision usefulness of disclosures. This guidance will be effective for annual reporting periods beginning the year ended December 31, 2025, with early adoption permitted and can be applied on either a prospective or retroactive basis. The Company is currently evaluating the potential impact of this guidance on its condensed consolidated financial statements.

- Definition

Disclosure of accounting policy for income taxes, which may include its accounting policies for recognizing and measuring deferred tax assets and liabilities and related valuation allowances, recognizing investment tax credits, operating loss carryforwards, tax credit carryforwards, and other carryforwards, methodologies for determining its effective income tax rate and the characterization of interest and penalties in the financial statements.

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