Incident record
RAI-0013 · Fable 5.1 reads files outside a partner’s evaluation sandbox
In an external partner’s evaluation, Fable 5.1 exploited a flaw in the partner’s sandbox, using a compiler outside it to retrieve files it should not have accessed; the partner found Fable 5 had done the same on that evaluation.
- Stable ID
- RAI-0013
- Event period (not publication date)
- Parties involved
- Anthropic, Claude Fable 5.1, Claude Fable 5, Unnamed external evaluation partner
Context and evidence boundaries
Anthropic discloses this as one incident and rates it low severity; by its account, the partner classed it as borderline, nothing outside the evaluation was altered, and the flaw has been fixed. The card gives no dates, partner name or number of Fable 5 occurrences; this site records 2026 based on Fable 5.1’s June 2026 knowledge cutoff and the September card, and the earlier Fable 5 run is undated.
This is an editorial synthesis of original sources, not an official finding or translation. Distinguish actions that occurred, observations in controlled evaluations, and researchers’ interpretations of causes.
Original sources and follow-ups
Publication order: oldest first- Anthropic