AI Agent Runtime Evidence Attestation Letter

What the Letter Attests To

An AI agent runtime evidence attestation letter is not a statement of intent or a description of designed controls. It is a documented claim, signed by an accountable individual, that specific runtime behavior occurred and was captured in verifiable records over a defined period. This distinction matters because audit and regulatory reviewers increasingly expect evidence-backed assurances rather than narrative descriptions of policy.

Neither NIST AI RMF nor ISO/IEC 42001 prescribes a fixed template for this letter. Both frameworks instead define the underlying documentation and accountability practices the letter must accurately summarize. NIST AI RMF's Manage function calls for ongoing monitoring, documentation, and communication of risk treatment activities. ISO/IEC 42001 requires organizations to retain documented information as evidence of conformity within an AI management system. An attestation letter is the point where these framework requirements are translated into a signed, reviewable artifact tied to specific agent behavior rather than general governance intent.

Runtime Evidence Categories the Letter Depends On

Four categories of runtime evidence typically substantiate an attestation letter, and each corresponds to a distinct log source. Agent identity evidence comes from authentication or identity-provider logs establishing which credential or service account performed an action. Permission-grant evidence comes from authorization records showing what scopes, roles, or tool access an agent held at a specific point in time, since agents frequently operate under permissions that change between deployments. Tool-call logs are invocation records capturing the function or API calls an agent made, the parameters passed, and the outputs returned. Policy enforcement events are the allow, deny, or modify decisions produced by a policy enforcement point when an agent's requested action is evaluated against governance rules.

These categories map directly onto audit-record content requirements already codified in NIST SP 800-53's Audit and Accountability family, which specifies that audit records capture the event type, timestamp, source, outcome, and identity of the associated subject. Structuring runtime logs around these five fields gives each evidence category a consistent, auditable shape before any letter is drafted.