AI Hallucination Research › Regulators › Major advanced economies › SG › MAS › NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025 › White paper › Detail › Finding
AI Labs · published 2026-05-28 · methodology v2.1

Claude Sonnet 4.6 with web search

What the RLB Specialist Panel found
  • Question (paraphrased to protect IP): In the MAS Notice 637 (Amendment) 2024 PDF, what do the yellow highlights signify, and do they carry through into the final consolidated (untracked) version of MAS Notice 637?
  • AI's response: "Text highlighted in yellow in the MAS Notice 637 (Amendment) 2024 PDF consists of editorial annotations describing the nature or purpose of the changes being made — for example, notes explaining what a particular insertion or deletion achieves."
  • Regulator's text: The yellow-highlighted text in MAS Notice 637 (Amendment) 2024 has a specific, defined function within that amendment instrument that differs from the characterisation of editorial annotation offered by the model.
  • Why the AI went wrong: The model described the yellow highlights as editorial annotations explaining the nature of changes — a characterisation that has no basis in the amendment document's own conventions. The response appears to reflect the model generating a plausible account of what such highlights might mean in a tracked-changes document, rather than what MAS specified them to mean in this particular instrument. The resulting characterisation is coherent as a general description of a drafting aid but is wrong as a description of this document's formatting convention.
  • Cited source(s):
Impact for this audience

This finding, parallel to the Opus 4.7 finding on the same question, implicates the same RAG-to-generation failure mode in Claude Sonnet 4.6 with web search: the model generated a characterisation of yellow highlights as editorial annotations rather than retrieving or deferring on the document-specific convention. The fact that both models produce different but equally wrong characterisations of the same formatting element suggests this is a systematic failure mode for this content type rather than model-specific. The training data is unlikely to contain the specific MAS amendment convention, and neither model's retrieval layer surfaced the relevant passage — pointing to both a training data gap and a retrieval coverage gap for recent MAS amendment instruments.

References — raw findings (per AI model)
This finding also affects
← Previous finding Finding 2. Claude Opus 4.7 with web search Next finding → Finding 4. Claude Sonnet 4.6 with web search
Cite this finding

Each finding has a stable Citation ID (RLB-F-… for aggregated case-study findings, RLB-H-… for raw per-model hallucinations) — like a DOI, the ID always resolves to the canonical finding even if URLs change.

Plain text 
RegLeg Specialist Panel (2026). "Claude Sonnet 4.6 with web search — AI Labs." Citation ID: . RegLegBrief AI Hallucination Research, published 2026-05-28. https://reglegbrief.com/regulators/j3/sg/mas/notice-637-capital-adequacy-banks-2025/whitepaper/finding/q-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-v1-012--sonnet-46-websearch/
APA 7th edition 
RegLeg Specialist Panel. (2026). Claude Sonnet 4.6 with web search [Hallucination finding ]. RegLegBrief AI Hallucination Research. https://reglegbrief.com/regulators/j3/sg/mas/notice-637-capital-adequacy-banks-2025/whitepaper/finding/q-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-v1-012--sonnet-46-websearch/
Bluebook / OSCOLA (US + UK legal) 
RegLeg Specialist Panel, Claude Sonnet 4.6 with web search [], RegLegBrief AI Hallucination Research (May 28, 2026), https://reglegbrief.com/regulators/j3/sg/mas/notice-637-capital-adequacy-banks-2025/whitepaper/finding/q-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-v1-012--sonnet-46-websearch/.
BibTeX 
@misc{reglegbrief_,
  author    = {RegLeg Specialist Panel},
  title     = {Claude Sonnet 4.6 with web search},
  year      = {2026},
  publisher = {RegLegBrief AI Hallucination Research},
  note      = {Hallucination finding Citation ID: },
  url       = {https://reglegbrief.com/regulators/j3/sg/mas/notice-637-capital-adequacy-banks-2025/whitepaper/finding/q-NOTICE-637-CAPITAL-ADEQUACY-BANKS-2025-v1-012--sonnet-46-websearch/}
}
← Back to case study summary Case study detail →
About Citation IDs →