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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.

Reason code: mentions per chapter22 mentions of the term across 10 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapterOther chapter05 Patterns: 1 mention05 Patterns108 Regulatory Map: 3 mentions08 Regulatory Map311 AI Defined: 3 mentions11 AI Defined315 Deployment: 1 mention15 Deployment116 Fairness & XAI: 9 mentions16 Fairness & XAI918 EU AI Act: 1 mention18 EU AI Act119 Privacy & AI: 1 mention19 Privacy & AI120 Existing Law: 1 mention20 Existing Law121 AI Laws Worldwide: 1 mention21 AI Laws Worldwide122 Principles & Standards: 1 mention22 Principles & Standards1No mentions in the other 13 chaptersSource: the Body of Knowledgev0.5.0
Reason code: mentions per chapter22 mentions of the term across 10 of the 23 chapters of the Body of Knowledge; the chapters the glossary cross-references are drawn solid.Cross-referenced chapterOther chapter000102030405 Patterns: 1 mention105060708 Regulatory Map: 3 mentions3081011 AI Defined: 3 mentions31112131415 Deployment: 1 mention11516 Fairness & XAI: 9 mentions9161718 EU AI Act: 1 mention11819 Privacy & AI: 1 mention11920 Existing Law: 1 mention12021 AI Laws Worldwide: 1 mention12122 Principles & Standards: 1 mention12223Source: the Body of Knowledge v0.5.0
Mentions per chapter How often each chapter names the term, with the chapters the glossary cross-references drawn solid. The longest bar is where to read the term in use; bars spread across many chapters mark a term that runs through the discipline.
Mentions as a table
Mentions of Reason code per chapter
ChapterMentionsCross-referenced
00 Preface0No
01 Definition0No
02 Why Now0No
03 Values & Principles0No
04 The Stack0No
05 Patterns1Yes
06 The Role0No
07 Maturity Model0No
08 Regulatory Map3No
10 Reading List0No
11 AI Defined3No
12 Governance Program0No
13 Risk Management0No
14 Development0No
15 Deployment1No
16 Fairness & XAI9Yes
17 Incidents0No
18 EU AI Act1No
19 Privacy & AI1No
20 Existing Law1Yes
21 AI Laws Worldwide1No
22 Principles & Standards1No
23 AI Agents0No

Patterns that use this term

2 pattern pages use the term, most mentions first.

Reason code: related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedColour: stack layer of the pattern04 Runtime ControlsReason codeRelated terms (6)Adverse action notice · RelatedAdverse action noticeContest path · RelatedContest pathContestability · RelatedContestabilityDecision notice · RelatedDecision noticeExplainability · RelatedExplainabilityExplanation record · RelatedExplanation recordPatterns using it (2)Decision Notice & Contest Path, 5 mentions · Uses the termDecision Notice & Contest PathExplanation Artefact, 7 mentions · Uses the termExplanation Artefact
Reason code: related terms and patternsThe term at the centre; related terms on solid edges, the terms it is contrasted with on dashed edges, and the patterns that use it most in the colour of their layer.RelatedColour: stack layer of the pattern04 Runtime ControlsRelated terms (6)Adverse action notice · RelatedAdverse action noticeContest path · RelatedContest pathContestability · RelatedContestabilityDecision notice · RelatedDecision noticeExplainability · RelatedExplainabilityExplanation record · RelatedExplanation recordPatterns using it (2)Decision Notice & Contest Path, 5 mentions · Uses the termDecision Notice & Contest PathExplanation Artefact, 7 mentions · Uses the termExplanation ArtefactReason code
The term's neighbourhood Terms related to this one on solid edges, terms it is often confused with on dashed edges, and the patterns that use it most in the colour of their layer. Follow a dashed edge to check the distinction before you use either term.
Neighbourhood as a table
Neighbourhood of Reason code
FamilyItemRelation
Related termsAdverse action noticeRelated
Related termsContest pathRelated
Related termsContestabilityRelated
Related termsDecision noticeRelated
Related termsExplainabilityRelated
Related termsExplanation recordRelated
Patterns using itDecision Notice & Contest Path, 5 mentionsUses the term
Patterns using itExplanation Artefact, 7 mentionsUses the term
  • 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}
}