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 Singapore counsel 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 singapore counsel 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 Lawyers

Lawyers advising Singapore-incorporated banks and financial holding companies on the MAS Notice 637 amendment package are routinely asked three questions: which entities the Notice binds, what the amendment changes on commencement, and how to read the drafting conventions in the MAS amendment PDF. Each of those questions has a specific, verifiable answer on the face of the regulator's documents.

On the first question, paragraph 1.1 of MAS Notice 637 states that the Notice is issued pursuant to section 55(1) and section 65(2) of the Banking Act and applies to all Reporting Banks; financial holding companies sit under MAS's separate FHC framework issued under the Financial Holding Companies Act, not under any sibling 637-number instrument. On the second question, the MAS amendment package itself states on its cover that yellow-highlighted text is annotation describing the change and will not appear in the published untracked Notice on commencement. Both points are regulator-stated and primary.

If AI-drafted text is being incorporated into legal advice, every MAS instrument reference and every reading of an amendment drafting convention has to be verified against the actual MAS register and the actual cover note. The AI hallucinations tested by the RLB Specialist Panel are exactly the kind of confident-wrong assertion that slides past a first-draft review and shows up only when the client, the regulator, or opposing counsel cross-checks the cited 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 Lawyers

The taxonomy lens that matters most to Singapore counsel here is exposed fabrication under a regulatory-enforcement risk class. The Specialist Panel flagged both findings as FABRICATED_FACT events, meaning the AI assistant produced a clean, lawyer-shaped answer that is wrong at the level of the citation itself, not at the level of legal interpretation.

That is the failure mode lawyers should expect from current frontier AI on Singapore regulatory work: well-formed prose, plausible instrument names, and assured statements about drafting conventions, none of which match the regulator's published source. Legal drafting tools that integrate frontier AI without binding the model to verified MAS source text are likely to reproduce the same class of error. The lens is not about model intelligence; it is about whether the workflow forces a verbatim check against the regulator-issued text before the AI output enters a deliverable.

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 Lawyers teams should do

Three actions follow for any practice incorporating AI into Singapore banking-regulatory work.

First, treat every AI-asserted MAS instrument reference as an unverified working citation. Resolve each notice number against the MAS Notices and Directives register, and reject any notice the register does not list. The fabricated "Notice FHC-N637" would not have survived this step.

Second, when the AI characterises an amendment-PDF drafting convention, require the team to read the actual MAS cover note and footer text and treat the regulator's stated convention as authoritative. The yellow-highlight reading in the MAS amendment package is on the face of the cover note and controls.

Third, capture each AI-assisted memo through a short verification checklist: instrument name verified against register, paragraph reference verified against the published Notice, drafting-convention claims verified against the MAS cover note, and version verified against the consolidated Notice on commencement. The RLB Specialist Panel can supply the checklist template and the verified primary substrate for MAS Notice 637 on request.

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