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ClaudeDevs@ClaudeDevs · Jun 9, 2026

Claude Fable 5 is here. New model generation, new way of working. Here's how to get started in Claude Code and on the…

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Summary

Claude Fable 5 is now available with a new approach to AI assistance. Users can access it via Claude Code or API by specifying the model ID, with features like always-on thinking, simplified prompting, and auto mode for handling complex tasks.

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  1. #1

    Claude Fable 5 is here. New model generation, new way of working. Here's how to get started in Claude Code and on the Claude Platform: 🧵

    Claude@claudeai · Jun 9, 2026

    Introducing Claude Fable 5: a Mythos-class model that we’ve made safe for general use. Its capabilities exceed those of any model we’ve ever made generally available.

  2. #2

    In Claude Code, run /model and select Fable from the model picker, or switch directly with: /model claude-fable-5

  3. #3

    In the API, switch the model ID parameter to "claude-fable-5" in both the Messages API and Claude Managed Agents. For some accounts, an admin may need to enable access first. The /claude-api skill in Claude Code can help you build with Fable on the API.

  4. #4

    Start at the top of your difficulty range: something harder than you'd assume previous versions of Claude can accomplish. Pick a backlog item you'd scope at a week, let Fable 5 interview you for the spec, turn on auto mode, and check back in the morning.

  5. #5

    You may notice that Fable feels different. Thinking is always on, and responses can take longer. Effort controls how much it thinks. We recommend high as the default. In our evals, even low/medium often beat previous models at xhigh, so save xhigh for your hardest problems.

  6. #6

    Prompting gets simpler. Existing prompts or skills developed for prior models are often too prescriptive for Fable. We recommend reviewing and potentially updating or removing older instructions or skills if you find default performance to be better.

  7. #7

    Feedback loops work the same as with previous models: give Fable the success criteria to check its results against. This can be /goal in Claude Code or Outcomes in Claude Managed Agents.

  8. #8

    With multi-agent orchestration in Claude Managed Agents, you can use Fable to delegate work to dedicated agents using smaller models.

  9. #9

    Cybersecurity and biosecurity requests may auto-reroute to Opus 4.8 (shown in the UI, billed at Opus prices). Docs + prompting guide: platform.claude.com/docs/en/build-…