# Claude Platform Claude Platform release notes — September 1, 2026

- Product: Claude Platform (https://whatsnew.fyi/product/claude-platform)
- Vendor: Anthropic
- Date: 2026-09-01
- Original notes: https://platform.claude.com/docs/en/release-notes/overview#september-1-2026
- Permalink: https://whatsnew.fyi/product/claude-platform/releases/2026-09-01-claude-platform-release-notes-september-1-2026

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We've launched Claude Fable 5.1 ( claude-fable-5-1 ), the successor to Claude Fable 5 for long-running agentic coding, knowledge work, and research, alongside Claude Mythos 5.1 ( claude-mythos-5-1 ) f…

- **added** — Launched Claude Fable 5.1 model for long-running agentic coding, knowledge work, and research
- **added** — Launched Claude Mythos 5.1 model