SEC Staff Accounting Bulletin No. 121: Crypto Custody Accounting Rules

Staff Accounting Bulletin No. 121, issued in March 2022, requires any entity that safeguards crypto assets for platform users to recognize both an asset and a corresponding liability on its balance sheet at fair value. The rule’s impact has been seismic: it effectively triples the capital requirements for banks considering crypto custody services, as the liability recognition triggers regulatory capital charges under Basel III frameworks that were never designed for custodied assets. The SEC Crypto Task Force — launched January 21, 2025, and led by Commissioner Hester Peirce — has signaled SAB 121 reform through multiple 2025 actions: the April 25, 2025 “Know Your Custodian” roundtable specifically addressed custody barriers, and the Task Force issued guidance clarifying that registered investment companies and advisors may use state trust companies for custodying crypto assets, and that broker-dealers may hold crypto and tokenized assets subject to prescribed requirements. The December 11, 2025 DTC no-action letter further signals that traditional custody infrastructure is being integrated with blockchain-native systems.

The SAB 121 Framework

SAB 121 applies to entities that “safeguard crypto-assets held for their platform users.” The staff interprets “safeguard” broadly to include any entity that maintains the cryptographic keys necessary to access digital assets, whether through direct key custody, multi-signature arrangements, or smart contract-based custody mechanisms.

Balance Sheet Treatment

Under SAB 121, an entity must recognize:

1. A safeguarding asset measured at fair value of the crypto assets custodied, representing the entity’s obligation to return those assets.
2. A corresponding safeguarding liability measured at the same fair value, reflecting the obligation to the platform users.

This dual recognition departs from traditional custody accounting, where custodied assets are typically disclosed in footnotes rather than recognized on the balance sheet. For a bank holding $1 billion in custodied crypto assets, SAB 121 requires adding $1 billion to both the asset and liability sides of the balance sheet — significantly impacting capital ratios, leverage ratios, and risk-weighted asset calculations.

Fair Value Measurement

SAB 121 requires fair value measurement at each reporting date, meaning the recognized amounts fluctuate with crypto market prices. For entities holding volatile crypto assets, this creates earnings volatility through the income statement, even though the entity has no economic exposure to price changes — it merely custodies assets for others.

The FASB’s ASU 2023-08, which established fair value accounting for crypto assets held as investments, provides some measurement guidance. However, SAB 121’s application to custodied assets — where the entity does not own the assets — creates a different accounting paradigm that intersects with existing guidance on custodial arrangements under ASC 860 and ASC 405.

Banking Industry Impact

SAB 121’s most significant consequence has been its chilling effect on bank participation in crypto custody. Major custodian banks — BNY Mellon, State Street, Northern Trust — had announced or explored crypto custody services prior to SAB 121. After the bulletin’s issuance, most paused or limited their crypto custody offerings.

The mechanism is straightforward: when custodied crypto assets appear on a bank’s balance sheet as liabilities, they increase the bank’s risk-weighted assets for purposes of Basel III capital calculations. This means the bank must hold additional capital against the custodied assets — capital that generates no return, since the bank earns only custody fees on assets it does not own.

For a bank with a 10% capital requirement, custodying $10 billion in crypto assets under SAB 121 would require approximately $1 billion in additional regulatory capital. At typical bank returns on equity of 10-12%, this creates an implicit cost of $100-120 million annually — far exceeding potential custody fee revenue.

Security Token Implications

SAB 121’s impact on the tokenized securities market is particularly acute. Tokenized securities — whether equity, debt, or fund interests — require custody services from regulated entities. If banks cannot economically provide crypto custody due to SAB 121’s capital requirements, the secondary market infrastructure for security tokens is constrained.

The practical effect has been to channel security token custody toward non-bank entities — including broker-dealers and specialized custodians — that are not subject to the same Basel III capital requirements. This fragmentation creates regulatory arbitrage and potentially concentrates custody risk in less-capitalized entities.

Congressional Override Attempt

In May 2024, both the House and Senate passed a Congressional Review Act resolution (H.J.Res. 109) to overturn SAB 121. President Biden vetoed the resolution in June 2024, marking the first presidential veto of crypto-related legislation and demonstrating the political significance of digital asset regulation.

The veto preserved SAB 121 but generated bipartisan criticism of the SEC’s approach. Senators Cynthia Lummis and Kirsten Gillibrand — co-sponsors of the Responsible Financial Innovation Act — argued that SAB 121 exceeded the SEC’s statutory authority by effectively imposing prudential banking requirements through an accounting bulletin.

The SEC’s Office of the Chief Accountant subsequently issued limited relief for certain banking entities, acknowledging that SAB 121’s application to regulated bank custodians may produce “anomalous results.” This partial walk-back addressed the most egregious capital impact but did not resolve the fundamental accounting framework.

SAB 121 and the Special Purpose Broker-Dealer Framework

The SEC’s 2020 special purpose broker-dealer (SPBD) no-action position intersects directly with SAB 121. SPBDs are permitted to custody digital asset securities under specific conditions, including maintaining one-to-one reserves of customer digital assets. Under SAB 121, these custodied assets must appear on the SPBD’s balance sheet, impacting its net capital calculations under SEC Rule 15c3-1.

For SPBDs, the net capital impact is particularly significant because broker-dealer capital requirements are calculated differently than bank capital requirements. A broker-dealer must maintain minimum net capital (ranging from $5,000 to $250,000 depending on activities) plus a ratio-based requirement tied to aggregate indebtedness. SAB 121’s balance sheet recognition of custodied assets inflates aggregate indebtedness, potentially requiring additional capital that SPBDs — typically smaller firms than traditional custodian banks — may struggle to maintain.

Prometheum, which obtained SPBD approval in 2023, has publicly disclosed that SAB 121 compliance represents a significant operational cost. The firm’s custody infrastructure must accommodate both the on-chain asset management and the back-office accounting systems required to track fair value changes on a daily basis.

SAB 121 Reform Under New SEC Leadership

The SEC Crypto Task Force has identified SAB 121 as a priority reform area. Several potential modifications have been discussed:

Bank custodian exemption. The most widely discussed reform would exempt regulated bank custodians from SAB 121’s balance sheet treatment, recognizing that banks already maintain fiduciary obligations and capital adequacy requirements that make the additional balance sheet recognition redundant. The OCC, FDIC, and Federal Reserve have all expressed interest in this approach.

Tiered treatment. A tiered approach would distinguish between different types of crypto asset custody arrangements. Fully segregated custody (where the custodian holds assets in separate wallets per customer) would receive lighter treatment than omnibus custody (where customer assets are commingled in shared wallets). This distinction reflects the different risk profiles of these arrangements.

Footnote disclosure alternative. Some commenters have proposed replacing the balance sheet recognition with enhanced footnote disclosure, returning to the traditional custody accounting model while adding specific disclosures about crypto asset custody risks, cybersecurity measures, and key management procedures.

The SAB 121 reform timeline depends on the Office of the Chief Accountant’s review process, which operates independently from the Commission’s rulemaking process. Staff accounting bulletins can be modified or withdrawn by the staff without a formal Commission vote, making SAB 121 reform potentially faster than other regulatory changes.

Intersection with Token Compliance

For security token issuers, SAB 121 creates a compliance consideration at the custody layer. Tokens issued under Regulation D or Regulation A+ require that investors have access to qualified custody solutions. If SAB 121 constrains the supply of custody providers, it limits the addressable investor base for security token offerings. The accredited investor pool — already limited to approximately 24.3 million U.S. households — is further narrowed when institutional investors cannot access custody services through their existing banking relationships.

Platforms like Securitize and Prometheum have developed custody solutions that operate within the SAB 121 framework, absorbing the balance sheet impact as a cost of their business model. These specialized providers fill the gap left by traditional bank custodians, though they typically offer narrower service capabilities and higher fees.

tZERO has taken a different approach, partnering with third-party custody providers rather than operating its own custody infrastructure. This model shifts the SAB 121 compliance burden to the custody partner while allowing the ATS to focus on its core trading and market-making functions.

The relationship between SAB 121 and the broader ATS framework creates a layered compliance challenge: trading platforms must ensure that their custody arrangements comply with both the ATS regulatory requirements and SAB 121’s accounting treatment, while maintaining capital adequacy under their broker-dealer or transfer agent registrations.

Impact on Tokenized Fund Structures

SAB 121 has particular implications for tokenized fund structures. When a fund administrator or custodian holds tokenized fund interests on behalf of investors, SAB 121’s balance sheet treatment applies. For fund structures where the custodian holds both the underlying assets and the tokenized interests representing those assets, the accounting creates a double-recognition problem: the underlying assets are recognized on the fund’s balance sheet, and the tokenized interests representing those assets are recognized on the custodian’s balance sheet under SAB 121.

This double-recognition has no economic substance — it is an artifact of the accounting treatment applied to a new technology. The SEC Crypto Task Force roundtable on custody and settlement specifically addressed this issue, with several participants arguing that SAB 121 was designed for speculative crypto assets and should not apply to tokenized representations of traditional financial instruments.

Audit and Compliance Implications

SAB 121 creates significant audit complications for entities custodying crypto assets. External auditors must evaluate the fair value measurement of custodied assets at each reporting date, requiring access to reliable pricing data for tokens that may trade on multiple exchanges with divergent pricing.

Audit evidence challenges. For widely traded crypto assets like Bitcoin and Ethereum, fair value determination is relatively straightforward — auditors can reference pricing data from major exchanges and institutional data providers. For security tokens with limited secondary market activity, fair value determination requires more complex valuation approaches, including discounted cash flow analysis, comparable transaction analysis, or reference to the most recent offering price. The thin trading volumes on most ATS platforms create challenges for auditors seeking independent pricing verification.

Internal control requirements. SAB 121 effectively requires entities to maintain internal controls over both the cryptographic custody infrastructure (wallet management, key security, multi-signature procedures) and the accounting infrastructure (fair value measurement, liability recognition, income statement impact). The intersection of cybersecurity controls and financial reporting controls creates a compliance burden that many traditional custodians are not equipped to manage without significant investment in specialized personnel and systems.

SOC 2 Type II reports. Institutional investors and their auditors increasingly require SOC 2 Type II reports from crypto custody providers, covering the security, availability, and processing integrity of custody operations. These reports — typically costing $100,000-300,000 annually to obtain — add to the compliance cost that SAB 121 imposes on the custody ecosystem.

Comparison with International Accounting Treatment

SAB 121’s approach to custodied crypto assets diverges significantly from international accounting standards and practices in other major financial centers:

IFRS treatment. Under International Financial Reporting Standards, custodied assets are generally disclosed in notes to the financial statements rather than recognized on the balance sheet. The International Accounting Standards Board (IASB) has not issued guidance equivalent to SAB 121, meaning that banks in IFRS-reporting jurisdictions (including the EU, UK, and most of Asia) can provide crypto custody services without the balance sheet impact that constrains U.S. banks.

Swiss approach. FINMA has issued guidance permitting Swiss banks to custody crypto assets under existing banking license frameworks, with disclosure requirements but without mandatory balance sheet recognition. This lighter treatment has contributed to Switzerland’s emergence as a significant hub for institutional crypto custody, with banks like Sygnum and SEBA operating custody services under Swiss banking licenses.

Singapore approach. The Monetary Authority of Singapore (MAS) has adopted a risk-based approach that distinguishes between different types of digital asset custody. Custody of tokenized securities under Singapore’s Securities and Futures Act receives treatment analogous to traditional securities custody, without the additional balance sheet recognition required by SAB 121.

This international divergence creates a competitive disadvantage for U.S.-based custody providers and drives institutional custody activity offshore — a consequence that the SEC Crypto Task Force has acknowledged in its review of SAB 121.

For a comparison of custody approaches across jurisdictions, see our analysis of US vs. EU tokenization frameworks. For the custody frameworks governing digital securities, see our detailed guide. For platform-specific custody analysis, review our entity profiles of major SEC-compliant infrastructure providers. For the SEC’s official SAB 121 text, see the SEC Staff Accounting Bulletin page.