[sigmar]

Fable/mythos are the first models from anthropic that hide 100% of reasoning tokens. So it seems to me like we're about to get a lot more data about to what extent Chinese model progress has been a consequence of distillation techniques.

[tristanj]

This isn't correct, Claude hasn't displayed the raw chain of thought for any of the Claude 4 series models, which were released in May 2025. Sonnet 4.6/Opus 4.8 only display a summarized chain of thought, which is produced by a secondary model. Fable displays its summarized chain of thought in the same manner.

The thinking traces disappeared because Anthropic changed them to be hidden by default. The rationale for hiding it was that most people don't look at the thinking traces https://news.ycombinator.com/item?id=47664442 . You can reenable thinking traces in Claude code settings with the flag showThinkingSummaries: true.

[sigmar]

Qualified it with "100%" because claude4 models show the first few lines of the chain of thought:

>On Claude 4 models, the first few lines of thinking output are more verbose, providing detailed reasoning that's particularly helpful for prompt engineering purposes. Claude Mythos Preview summarizes from the first token, so its thinking blocks do not show this verbose preamble. https://platform.claude.com/docs/en/build-with-claude/extend...

[Barbing]

Hidden by default should make it easier to identify who’s scraping even those summarized CoTs, I figure. Also figure it’s very expensive to summarize every single chat on the service.