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Claude Code Updates Include Fable 5.1, New Time Formats, and Security Enhancements

Claude Code has been updated with the integration of Claude Fable 5.1 as the default Fable model, alongside new time formatting options and enhanced security features.

By Illumora Editorial

Source · Sep 1, 2026, 5:53 PM · On Illumora · Sep 1, 2026, 5:57 PM

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Read the source →Claude Code What's New + releases — Claude Code changelog - Claude Code Docs
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Recent updates to Claude Code introduce Claude Fable 5.1, which now serves as the default Fable model. This new model offers a 1M context window.

Users can now customize time displays within Claude Code, and several security and operational improvements have been implemented.

Key Points

  • Claude Fable 5.1 is now the default Fable model, featuring a 1M context window.
  • Claude Fable 5.1 pricing is $10 per million tokens for input and $50 per million tokens for output, with cache reads at $0.25 per million tokens.
  • New timeFormat and timeZone settings allow users to select 12-hour, 24-hour, 24-hour UTC, or a strftime pattern for turn-end clock and transcript-view timestamps.
  • A Containment Escape rule has been added to auto mode, preventing automatic approval of cloud metadata-credential fetches, egress evasion, and cross-tenant reach unless explicitly marked as expected by the environment.
  • The CLAUDE_CODE_SUBAGENT_MODEL_FORCE setting can now apply the CLAUDE_CODE_SUBAGENT_MODEL (or the main model) to all subagents, overriding per-spawn and agent-definition model settings.
  • A /doctor warning has been introduced for stale sandbox mask files resulting from killed sessions.
  • A one-time prompt in auto mode now appears before the first file read outside working directories, offering the option to block such reads via permissions.blockReadsOutsideWorkingDirectories.

Context

According to the Claude Code changelog, these updates enhance both the capabilities and the security posture of the platform. The introduction of Claude Fable 5.1 provides users with a larger context window for their tasks. The new time formatting options offer greater flexibility in how time-related information is displayed.

Why It Matters

The integration of Claude Fable 5.1 provides users with a more powerful default model, potentially enabling more complex and extensive coding tasks. The added security rules and warnings aim to reduce potential vulnerabilities and improve operational hygiene, which can be critical for developers working with sensitive data or in regulated environments.

What To Do

  • Review the pricing structure for Claude Fable 5.1 to understand potential cost implications for your projects.
  • Explore the new timeFormat and timeZone settings to customize your display preferences.
  • Note the new Containment Escape rule and adjust your environment configurations if certain metadata-credential fetches or egress activities are expected.
  • Consider using CLAUDE_CODE_SUBAGENT_MODEL_FORCE if consistent model application across subagents is desired.
  • Watch for /doctor warnings regarding stale sandbox mask files and address them to maintain a clean working environment.