AI Weekly Malaysia

Researchers demonstrated that encrypted reasoning blocks returned by OpenAI, Anthropic, and Google APIs could be replayed into another session and fed to a weaker model in the same provider family to reveal hidden reasoning and secrets. Across 6,708 public agent trajectories they decoded 315,320 thinking blocks and found 704 real privacy artifacts including 62 API keys, 33 passwords, 24 access tokens, and 7 private keys. All affected providers and platforms applied mitigations and the main extraction attack is no longer reproducible as of August 2026.

Why: If you ship agents or share agent logs publicly, strip reasoning blocks and opaque reasoning fields from traces before publishing—sanitizing only the visible text is not enough because encrypted reasoning objects can carry API keys, passwords, and tokens. Avoid committing raw API transcripts to repos or issue trackers even when the visible output looks clean.

Researchers found that OpenAI, Anthropic, and Google encrypted chain-of-thought reasoning blocks returned via their APIs could be replayed into weaker sibling models in the same family (which shared the same encryption key) and jailbroken into outputting the raw plaintext reasoning. Claude Haiku 4.5 was the easiest to attack using a prompt that asked it to transcribe reasoning verbatim inside a thinking-copy tag. All providers acknowledged the report and patched the issue.

Why: If you build on proprietary reasoning APIs, this reveals that encrypted reasoning blocks are portable across sessions and models within a family, and that weaker models can be coerced to decrypt them. The attack is patched, but the paper's appendix exposes what raw reasoning traces actually look like inside frontier models—useful for anyone evaluating whether to rely on reasoning_effort parameters or build agent pipelines around hidden CoT.