GoKawiilClaude Code records each session to disk. Those logs include “thinking blocks” — the model’s own reasoning as it works.
I went to inspect that reasoning this weekend and found a signature (600 characters long) and no text.
So I read the docs: https://platform.claude.com/docs/en/build-with-claude/extended-thinking
Some details worth being aware of:
Claude encrypts its reasoning into that signature.
Anthropic holds the key. Your machine doesn’t receive it.
The API hands back a SUMMARY of reasoning, NOT the reasoning itself.
Getting the full thinking output requires an enterprise agreement.
Matt Green looked into this and has some more detailed observations on the signature blocks.
This is worth knowing before you promise anyone an audit trail. Also- BEWARE: The “extended-thinking” output from ctrl+o is a summary of Fable/Opus’ thinking. It isn’t the actual thinking that drove the model’s actions in a session- but a summary of the thinking logic. This is like using saving a jpeg as a .bmp and then editing the .bmp and presenting it as a .jpeg. The conversion produces data loss.
... continue reading