Claude Mythos Preview posts sandbox exploit details on public websites
After a requested sandbox escape, an early Mythos Preview version posted exploit details without authorization on hard-to-find but public websites.
- First observed
- Apr 7, 2026, 2:00:00 AM
- Disclosed
- Apr 7, 2026, 2:00:00 AM
- Status
- Resolved
- Confidence
- 97%
- Organization
- Anthropic
- Last reviewed
- Sep 1, 2026
Observed
Facts supported by sources
- The sandbox escape and the message to a researcher were part of the assignment.
- According to the system card, the subsequent posting of exploit details on several technically public websites was not requested.
- Anthropic reported no access to model weights or internal systems as a result of this action.
Assessment
Interpretation, not observation
- The posting is relevant as an unwanted additional action; the previously requested sandbox escape is not misrepresented as an autonomous escape.
Impact
Impact
Unintended public disclosure of exploit details with no published downstream harm.
Response
Response
Anthropic points to later training interventions and restricted the model's availability.