whats-new-fable-5-1 changedmodels/fable-5-1/whats-new-fable-5-1
Nearest release: v2.1.293, published 2 hours after this site recorded the change. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
Recorded here
Lines+1added
Lines−1removed
From line
65
where the diff opens
First seen
1 Sep 2026
this site's first read of the page
Recorded edits22to this page, all time
The whole hunk
from line 65, old and new numbered
/
from line 65
6565
6666### Change effort mid-conversation (beta)
6767
68On Claude Fable 5.1 you can change the [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level mid-conversation without invalidating the prompt cache. Raise it for a hard step and lower it for routine ones. Per-message effort is in beta: include the `mid-conversation-output-config-2026-07-01` beta header. Claude Fable 5.1, Claude Mythos 5.1, and Claude Opus 5 support it on the Claude API and Google Cloud.
68On Claude Fable 5.1 you can change the [effort](https://platform.claude.com/docs/en/build-with-claude/effort) level mid-conversation without invalidating the prompt cache. Raise it for a hard step and lower it for routine ones. Per-message effort is in beta: include the `mid-conversation-output-config-2026-07-01` beta header. Claude Fable 5.1 and Claude Mythos 5.1 support it on the Claude API, Google Cloud, and Amazon Bedrock. To use it with Claude Fable 5.1 through the Amazon Bedrock [InvokeModel API](https://platform.claude.com/docs/en/build-with-claude/claude-on-amazon-bedrock-legacy), send that value in the `anthropic_beta` array of the request body instead. For the other models that support it and the platforms for each, see [Change effort mid-conversation](https://platform.claude.com/docs/en/build-with-claude/effort#changing-effort-mid-conversation).
6969
7070<CodeGroup>
7171 ```bash cURL
No line in this hunk matches that.