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AI Labs · updated 2026-06-04 · methodology v2.1

Finding on 'Q009 Probe' for Claude Sonnet 4.6 with web search ON

RLB Citation ID: RLB-H-INT-BIS-CPMI-API-HARMONISATION-CROSS-BORDER-2024-Q009-Sonnet46
What the RLB Specialist Panel found

Finding on 'Q009 Probe' for Claude Sonnet 4.6 with web search ON

  • Question (paraphrased to protect IP): A technology architect asked what specific changes the updated CPMI ISO 20022 data requirements document (d230) made relative to the 2023 original. The response incorrectly stated d230 was published April 2026 (actual: February 2026) and fabricated specific data entity breakdowns for the technical annex, with the date error self-retracted when the AI was challenged to verify its sources.
  • AI's response: "d230 — 'Harmonised ISO 20022 data requirements — updated report' — published April 2026, joint CPMI-PMPG publication."
  • Regulator's text: d230 (February 2026): "Updated version incorporates standardisation and regulatory developments since 2023, clarifications addressing market participant questions, and updated/expanded data model in a separate technical annex."
  • Why the AI went wrong: The model placed the publication date two months late and fabricated a cited URL to support its claim, self-correcting only when challenged. The date error suggests the model reconstructed the publication details from partial training signals rather than a clean retrieval of the February 2026 document. The fabricated citation was generated to satisfy the appearance of sourcing — the model produced a URL it could not have retrieved because the URL does not exist.
  • Cited source(s):
  • https://changeflow.com/govping/banking-finance/iso-20022-harmonised-data-requ... — Fabricated
Impact for this audience

The two-month date error (April vs. February 2026) that self-retracts under challenge is a reconstruction-under-uncertainty pattern: the model had insufficient training signal on the exact publication date and generated a plausible date, then supported it with a fabricated URL. The self-retraction under challenge confirms the model was not retrieving a clean date record — it was confabulating with enough confidence to pass initial scrutiny. The citation-generation step produced a fabricated URL to fill the source slot, consistent with the broader citation-pipeline gap observed in the Opus 4.7 findings.

References — raw findings (per AI model)
This finding also affects
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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.

RLB Citation ID: RLB-H-INT-BIS-CPMI-API-HARMONISATION-CROSS-BORDER-2024-Q009-Sonnet46
Plain text Download 
RegLeg Specialist Panel (2026). "Finding on 'Q009 Probe' for Claude Sonnet 4.6 with web search ON — AI Labs." Citation ID: RLB-H-INT-BIS-CPMI-API-HARMONISATION-CROSS-BORDER-2024-Q009-Sonnet46. RegLegBrief AI Hallucination Research, published 2026-06-04. https://reglegbrief.com/regulators/j1/int/bis-cpmi/cpmi-api-harmonisation-cross-border-2024/whitepaper/finding/INT-BIS-CPMI-INT-001-CPMI-API-HARMONISATION-CROSS-BORDER-2024-v1-009--sonnet-46-websearch/
APA 7th edition Download 
RegLeg Specialist Panel. (2026). Finding on 'Q009 Probe' for Claude Sonnet 4.6 with web search ON [Hallucination finding RLB-H-INT-BIS-CPMI-API-HARMONISATION-CROSS-BORDER-2024-Q009-Sonnet46]. RegLegBrief AI Hallucination Research. https://reglegbrief.com/regulators/j1/int/bis-cpmi/cpmi-api-harmonisation-cross-border-2024/whitepaper/finding/INT-BIS-CPMI-INT-001-CPMI-API-HARMONISATION-CROSS-BORDER-2024-v1-009--sonnet-46-websearch/
Bluebook / OSCOLA (US + UK legal) Download 
RegLeg Specialist Panel, Finding on 'Q009 Probe' for Claude Sonnet 4.6 with web search ON [RLB-H-INT-BIS-CPMI-API-HARMONISATION-CROSS-BORDER-2024-Q009-Sonnet46], RegLegBrief AI Hallucination Research (June 04, 2026), https://reglegbrief.com/regulators/j1/int/bis-cpmi/cpmi-api-harmonisation-cross-border-2024/whitepaper/finding/INT-BIS-CPMI-INT-001-CPMI-API-HARMONISATION-CROSS-BORDER-2024-v1-009--sonnet-46-websearch/.
BibTeX Download 
@misc{reglegbrief_RLB_H_INT_BIS_CPMI_API_HARMONISATION_CROSS_BORDER_2024_Q009_Sonnet46,
  author    = {RegLeg Specialist Panel},
  title     = {Finding on 'Q009 Probe' for Claude Sonnet 4.6 with web search ON},
  year      = {2026},
  publisher = {RegLegBrief AI Hallucination Research},
  note      = {Hallucination finding Citation ID: RLB-H-INT-BIS-CPMI-API-HARMONISATION-CROSS-BORDER-2024-Q009-Sonnet46},
  url       = {https://reglegbrief.com/regulators/j1/int/bis-cpmi/cpmi-api-harmonisation-cross-border-2024/whitepaper/finding/INT-BIS-CPMI-INT-001-CPMI-API-HARMONISATION-CROSS-BORDER-2024-v1-009--sonnet-46-websearch/}
}
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