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Claude Code Updates Include Fable 5.1 Integration and Security Enhancements

Claude Code has integrated Claude Fable 5.1 as its default Fable model, offering a 1M context window and new pricing, alongside security and usability improvements.

By Illumora Editorial

Source · Sep 1, 2026, 10:33 PM · On Illumora · Sep 1, 2026, 10:37 PM

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Read the source →Claude Code What's New + releases — Claude Code changelog - Claude Code Docs
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Claude Code has released updates that include the integration of Claude Fable 5.1 and several new features and bug fixes. Claude Fable 5.1 is now the default Fable model, providing a 1M context window.

Key Points

  • Claude Fable 5.1 is now the default Fable model in Claude Code.
  • Claude Fable 5.1 offers a 1M context window.
  • Pricing for Claude Fable 5.1 is $10/$50 per Mtok, with cache reads at $0.25/Mtok.
  • A Containment Escape rule has been added to auto mode to prevent automatic approval of cloud metadata-credential fetches, egress evasion, and cross-tenant reach.
  • New timeFormat and timeZone settings allow customization of the turn-end clock and transcript-view timestamps.
  • A one-time prompt in auto mode now appears before the first file read outside working directories, offering an option to block such reads.
  • Support for a gateway-supplied description on discovered /model picker entries has been added.
  • Claude Code fixed a regression that prevented launching on macOS 12 (Monterey).

Context

According to the Claude Code changelog, these updates introduce new capabilities and address previous issues. The integration of Claude Fable 5.1 expands the model's context handling. Security enhancements, such as the Containment Escape rule and the prompt for file reads outside working directories, aim to improve control over operations. Usability features like time format settings and model override options provide more flexibility for users.

Why It Matters

These updates offer builders enhanced model capabilities through Claude Fable 5.1's larger context window and more granular control over security and operational settings within Claude Code. The pricing structure for the new model also provides transparency for cost management.

What To Do

  • Note the new pricing for Claude Fable 5.1 at $10/$50 per Mtok for input/output and $0.25/Mtok for cache reads.
  • Review the new Containment Escape rule and consider its implications for cloud metadata-credential fetches and egress evasion in auto mode.
  • Test the new timeFormat and timeZone settings to customize timestamp displays.
  • Observe the one-time prompt for file reads outside working directories and evaluate the permissions.blockReadsOutsideWorkingDirectories option.

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