Data-minimization principle
Medical artificial intelligence agents should retrieve patient identifiers only when a task requires them, the data-minimization principle behind the HIPAA minimum necessary standard for protected health information (PHI).
Silent access problem
An agent can retrieve identifiers without revealing them. Such silent access remains invisible to evaluations that inspect only the output.
Canary-based measurement
We embedded canaries in synthetic patient records and linked each tool invocation to canary exposure in the final answers across five language models, four boundary levels, and seven attack frames for identifier-free clinical tasks.
Findings
- Three models invoked the PHI tools unnecessarily, whereas Claude Opus 4.8 and GPT-5.5 did not.
- Stronger boundaries reduced this access, and the residual access under the strictest policy was confined to frames in which the user overrode the policy or asserted approval.
- A pre-execution gate given the task-necessity criterion nearly eliminated this access.
Evaluation requirements
Output-only evaluation cannot verify minimum-necessary access; boundaries, gates, and access-log audits are required together.