Source-Credit Fabrication on MAS Notice 637 (Amendment) 2025. Two frontier AI subjects tested by the RLB Specialist Panel produced confident, lawyer-shaped answers on the MAS Notice 637 risk-based capital adequacy for Reporting Banks that do not reconcile to the regulator-issued source. One invented an FHC-numbered MAS notice that does not exist; the other misread the regulator's own amendment-drafting convention. Both events sit in the same exposed-fabrication class.

The pattern in one line

For In-house legal at Singapore corporate-banking divisions the pattern is clean: leading AI assistants will name a MAS instrument with the wrong number and will read a regulator-stated drafting convention against the cover note, in confident prose, with no flag of low confidence.

How the RLB Specialist Panel tested this

Questions are prepared by the RLB Specialist Panel based on real practical AI usage in the workflows in-house legal at singapore corporate-banking divisions use AI for: regulatory-perimeter mapping for the MAS Notice 637 (Amendment) 2025 amendment cycle, and amendment-package reading where the cover note carries the controlling drafting convention. Each question is recorded against verbatim regulator-issued source text held by the Panel as primary substrate.

The Panel asked two frontier AI subjects to answer in their normal application register, then bound each answer to the corresponding paragraph of MAS Notice 637 and the corresponding cover-note language in the MAS Notice 637 amendment package. Where the AI assertion contradicted the verbatim regulator text the Panel recorded a FABRICATED_FACT finding under exposed_fabrication.

What the models got wrong

Finding 1: Fabricated "Notice FHC-N637" for financial holding companies. Opus 4.7 asserted that financial holding companies incorporated in Singapore are covered by a separate notice typically called "Notice FHC-N637 (Risk Based Capital Adequacy Requirements for Financial Holding Companies)". The MAS Notices and Directives register does not list any such instrument. The actual MAS Notice 637 applies, by paragraph 1.1, to Reporting Banks issued under the Banking Act; FHCs sit under a separate MAS notice issued under the Financial Holding Companies Act.

Claude Opus 4.7 produced the assertion in response to a question about how MAS Notice 637 applies to financial holding companies; Claude Sonnet 4.6 was tested as the comparator subject in the broader Panel run. The AI output reads as a lawyer-shaped citation, but the cited notice number is not on the MAS Notices and Directives register. Citation ID RLB-H-SG-MAS-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-Q010-Opus47.

Finding 2: Misrepresented yellow-highlight meaning in MAS amendment PDFs. Opus 4.7 characterised the yellow highlighting in the MAS Notice 637 amendment PDF as a drafting or visual aid drawing attention to defined terms, cross-references, or items to read carefully. The MAS amendment package itself states on its face that yellow-highlighted text is annotation describing the change, and will not appear in the published untracked Notice. The AI characterisation contradicts the regulator's own cover note. Claude Opus 4.7 produced the yellow-highlight characterisation in response to a Specialist Panel application-style question on how to read the MAS Notice 637 amendment package.

The reading directly contradicts the cover-note convention on the face of the MAS PDF. Citation ID RLB-H-SG-MAS-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-Q012-Opus47.

Why this matters for Legal

In-house legal at a Singapore corporate-banking division handles the group-capital regulatory perimeter for the Reporting Bank and, where applicable, the financial holding company above it. Each MAS instrument reference in a legal opinion, a regulator-facing letter, or a transaction document has to be a real instrument with a correct title, and each drafting-convention claim has to track the regulator's cover-note language.

Both AI hallucinations tested by the RLB Specialist Panel directly threaten those outputs. The fabricated "Notice FHC-N637" would route an opinion on FHC-level capital obligations through an instrument that does not exist. The amendment yellow-highlight misreading would produce a legal characterisation of the amendment that contradicts the MAS cover note. Both errors travel forward into the legal record and surface on external review or supervisor challenge.

For a legal function that relies on AI for drafting velocity, the operational rule is that the AI output enters the opinion only after the cited instrument and the cited drafting convention have been verified against the regulator's source.

The regulator's actual position

On the FHC perimeter, MAS Notice 637 states on the face of the Notice: "This Notice is issued pursuant to section 55(1) and section 65(2) of the Banking Act and applies to all Reporting Banks. [...] 11.2.2 A Reporting Bank need not comply with the requirements in this Part if it is a subsidiary of (a) another Reporting Bank which is subject to the requirements in this Part; or (b) a financial holding company which is subject to requirements similar to that set out in this Part." The Reporting Bank perimeter is therefore explicit in the Notice itself, and the FHC framework sits under a separate MAS notice issued under the Financial Holding Companies Act, not under a sibling 637-number instrument.

On the amendment yellow-highlight convention, the MAS Notice 637 amendment package states on its cover: "Text which is highlighted in yellow are annotations to describe changes, and will not appear in the published untracked version of MAS Notice 637. For instance, where amendments have been made to a selected paragraph of an Annex, only that paragraph will be reflected in this document, prefaced with the following explanatory text in yellow highlights: [Amendments to paragraph xx]." The convention is regulator-stated and controlling; any reading that treats the yellow text as substantive new Notice content is against the regulator's own cover-note language.

What this tells us about AI for Legal

The lens for in-house legal is exposed fabrication producing written-opinion risk. The Specialist Panel categorised both findings as FABRICATED_FACT, which in a legal-opinion context translates directly into citation-defect risk: a cited MAS instrument that does not exist, or a cited drafting convention that contradicts the regulator's cover note.

For the function the implication is that AI cannot replace the verbatim source check on MAS instrument references or drafting-convention readings. AI tools that integrate frontier models without binding them to verified MAS source text will reproduce this class of error, and the propagation path through opinions, regulator-facing letters, and transaction documents is direct.

What the RLB Specialist Panel is doing about it

The Panel records each error against the verbatim regulator-issued source, names the AI subject, and binds the finding to a specific paragraph of MAS Notice 637 or the specific cover-note language in the amendment package. Findings are released publicly with the Citation IDs, the substrate document reference, and the operational consequence for each affected audience. Where firms want to take the Panel's verified primary substrate inside their own AI workflow, the Panel runs a partnership track that supplies the substrate package, the verification protocol, and a per-finding regression test set.

The partnership track is the operational answer to the class of failure on display in RLB-H-SG-MAS-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-Q010-Opus47 and RLB-H-SG-MAS-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-Q012-Opus47.

What Legal teams should do

Three actions follow for in-house legal.

First, every MAS instrument reference in an AI-drafted legal opinion should be resolved against the MAS Notices and Directives register before the opinion is signed. The fabricated "Notice FHC-N637" would have failed this step; FHC-level obligations sit under MAS's separate notice issued under the Financial Holding Companies Act.

Second, any AI-drafted characterisation of the amendment drafting convention should be checked against the MAS cover note directly, and the opinion should quote the cover note when it relies on the convention. AI gloss that contradicts the cover note should be rejected before the opinion enters the legal record.

Third, legal should hold a short AI-output verification protocol for every regulatory opinion: instrument name verified against MAS register, paragraph cited verified against published Notice, drafting-convention reading verified against cover note, version reconciled against the consolidated Notice. The RLB Specialist Panel can supply the protocol and the verified primary substrate.

Right of Reply

These findings and associated work have been put up in public with a view of the greater good for the development of a safer AI ecosystem. Any party reading this or any finding on reglegbrief.com may contact us and have an unconditional right of reply; the Specialist Panel will publish any factual correction or contextual response alongside the original finding, with no editorial gatekeeping. Researchers, regulators, and compliance teams with questions on methodology or specific findings can reach the Specialist Panel via the same channel.

Source & Methodology Standards

RegLeg Brief is operated by Verdus Technologies Pte. Ltd. (UEN 201616982R), incorporated in Singapore. The RLB Specialist Panel, with an aggregate of over 60 years of public-policy and industry experience, documents only confirmed hallucination findings, under a methodology that requires a verbatim regulator excerpt for every documented claim. All findings, citation IDs, model outputs, regulator excerpts, and methodology notes are open-access.

Primary source verified: MAS Notice 637 (Amendment) 2025, Risk Based Capital Adequacy Requirements for Banks Incorporated in Singapore · Substrate documents: mas-notice-637-amendment-2025.pdf, mas-notice-637-effective-2025-12-31.pdf · MAS portal: mas.gov.sg

Citation IDs referenced:

• RLB-H-SG-MAS-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-Q010-Opus47
• RLB-H-SG-MAS-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-Q012-Opus47