The whole hunk
from line 23, old and new numbered
/
lines
from line 23
2323* `thinking.display` accepts a third value, `"updates"`, in beta (`thinking-display-updates-2026-08-18` header). Reasoning comes back with an empty `thinking` field, as under `"omitted"`, and the short progress updates that Claude Fable 5.1, Claude Mythos 5.1, and Claude Fable 5 write between tool calls come back as text, at most one `thinking` block before a tool call. See [Progress updates between tool calls](https://platform.claude.com/docs/en/build-with-claude/thinking#progress-updates).
2424* Text generated by Claude Fable 5.1 and Claude Mythos 5.1 carries Anthropic's text watermark, and supported image and video files that Claude produces through the [code execution tool](https://platform.claude.com/docs/en/agents-and-tools/tool-use/code-execution-tool) carry C2PA Content Credentials when you retrieve them through the [Files API](https://platform.claude.com/docs/en/build-with-claude/files) on the Claude API. Marking requires no changes to your requests or response handling.
2525* Like Claude Fable 5, both models require 30-day data retention and aren't available under zero data retention unless expressly authorized by Anthropic. See [Model-specific data retention requirements](https://platform.claude.com/docs/en/manage-claude/api-and-data-retention#model-specific-data-retention-requirements).
26* The guides for the Claude Enterprise endpoints of the [Admin API](https://platform.claude.com/docs/en/api/admin) ([user management](https://platform.claude.com/docs/en/manage-claude/user-management) and [spend limits](https://platform.claude.com/docs/en/manage-claude/spend-limits-api)), the [Claude Enterprise Analytics API](https://platform.claude.com/docs/en/manage-claude/analytics-api), and the [Compliance API](https://platform.claude.com/docs/en/manage-claude/compliance-api) now show the `anthropic-version` header; send it on every request to these endpoints, as in the rest of the Claude API. See [API versions](https://platform.claude.com/docs/en/api/versioning).
2627
2728### August 27, 2026
2829