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Reason code

By Updated

A stable, human-readable statement of a principal factor behind an adverse decision, mapped from the factors the model actually scored and versioned with the model; required in substance by US adverse-action rules 1.

Developed in
ch. 16, Credit: adverse-action notices and reason codes
ch. 05, Pattern: Decision Notice & Contest Path
ch. 05, Pattern: Explanation Artefact
Chapters
ch. 05, Patterns · ch. 16, Fairness & XAI · ch. 20, Existing Law
Source
1 numbered reference, listed below

Where it is used

10 chapters of the Body of Knowledge use the term. Each link opens the first section that does.

Patterns that use this term

2 pattern pages use the term, most mentions first.

  • Contest path

    The route by which a person affected by an automated decision reaches a reviewer who did not take the original decision, sees the inputs, the reasons and the…

  • Contestability

    The ability of a person affected by an AI-supported decision to challenge it and obtain a response that can change it.

  • Decision notice

    The notice a person receives at the point of an automated or AI-assisted decision, rendered from a versioned template and the decision record: that a system…

  • Explanation record

    The evidence artefact for one explained decision: model version, explanation method and version, baseline, reason codes, counterfactual, template, audience…

  • Adverse action notice

    The notice a US creditor must give when it denies or worsens credit, stating the specific principal reasons.

  • Explainability

    In NIST's framing, a representation of the mechanisms behind a system's operation: how a decision was made.

Sources

  1. [1] 12 CFR 1002.9 (Regulation B, notifications) (1002.9(b)(2) statement of specific principal reasons for adverse action; Supplement I commentary; text as of 2026-09-01). eCFR. 2026-09-01. https://www.ecfr.gov/current/title-12/chapter-X/part-1002/section-1002.9 (verified: primary)

Definitions of legal terms paraphrase the cited text, which governs. Dated statements are as of .

Cite this term

García Aibar, J. (2026). Reason code. In AI Governance Engineering: The Thesis & Body of Knowledge (v0.5.0), Glossary. https://doi.org/10.5281/zenodo.22956197. https://aigovernanceengineer.com/glossary/reason-code. CC BY 4.0

BibTeX

@misc{aige2026reasoncode,
  author  = {Jorge García Aibar},
  title   = {{Reason code}},
  note    = {Glossary, AI Governance Engineering: The Thesis \& Body of Knowledge, version 0.5.0},
  year    = {2026},
  doi     = {10.5281/zenodo.22956197},
  url     = {https://aigovernanceengineer.com/glossary/reason-code}
}