Fable 5.1 becomes the default model in Claude Code 2.1.257

Anthropic has made Claude Fable 5.1 the default Fable model in Claude Code 2.1.257, with a 1M context window. The release lists $10/$50 per Mtok and $0.25/Mtok cache reads, alongside new controls for permissions, subagents, and time displays.

According to GitHub's release notes, Claude Code also adds descriptions supplied by a gateway to discovered model-picker entries. Entries without a description continue to display “From gateway,” when gateway model discovery is enabled.

At a glance

• CLAUDE_CODE_SUBAGENT_MODEL_FORCE applies the configured subagent model, or the main model, to every subagent, overriding model choices specified when an agent is spawned or in its agent definition.
• Auto mode now requires approval for cloud metadata credential fetches, egress-evasion attempts, and cross-tenant reach unless an environment explicitly marks them expected, and it presents a one-time prompt for outside-directory reads.
• New timeFormat and timeZone settings support 12-hour, 24-hour, 24-hour UTC, and strftime-based clocks for turn-end and transcript timestamps, while /effort gains a session-only setting.

The package appears to shift more operational decisions into explicit session and policy controls while reducing friction in long-running work. A 1M-context default model and inexpensive cache reads may be consequential where conversation history, background activity, and subagent coordination persist across a Claude Code workflow. The new permission rules likely make auto mode less permissive when operations cross an environment boundary.

CLAUDE_CODE_SUBAGENT_MODEL_FORCE overrides per-spawn model choices

CLAUDE_CODE_SUBAGENT_MODEL_FORCE applies CLAUDE_CODE_SUBAGENT_MODEL to every subagent. If no subagent model is configured, it applies the main model instead. The variable ignores model overrides supplied for an individual spawn and those specified in agent definitions, making the selected model consistent across a session’s subagents.

The update also adds the s option to /effort, which changes effort for the current session only and matches the existing /model behavior. New timeFormat and timeZone settings control the turn-end clock and timestamps in transcript view. Supported formats include 12-hour, 24-hour, 24-hour UTC, or a strftime pattern.

Containment Escape rule covers cloud metadata and cross-tenant reach

Claude Code adds a Containment Escape rule to auto mode for cloud metadata-credential fetches, egress evasion, and cross-tenant reach. These operations are no longer automatically approved unless the environment marks them expected. Auto mode also displays a one-time prompt before the first file read outside working directories, with an option to block those reads.

The outside-read option is named permissions.blockReadsOutsideWorkingDirectories. Separately, project-level .claude/settings.json and .claude/settings.local.json can no longer set defaultMode to bypassPermissions, matching the treatment of auto mode. The release also makes --add-dir, /add-dir, and additionalDirectories reject network paths before accessing them, including UNC shares and /net/<host> automounts.

VS Code adds a model pill and an Archived sessions group

The VS Code extension adds collapsible ACCOUNT & USAGE and SESSION MANAGER headers to its session-list panel. The account area contains the account email, a usage meter, and a View details link to the usage dialog. Its input footer now includes a model pill that opens the picker, with an Effort row and a More models page.

The extension also renames Delete session to Archive session. Archived sessions move to a collapsible Archived sessions group at the bottom of the list and receive an Unarchive action. Slash commands now open in a filterable dialog from the action menu, while the MCP servers dialog receives the same filter box. Output-style selection, including custom styles, is also added.

Gateway aliases remain on Fable 5 In Claude apps gateway sessions, the fable and best aliases continue to resolve to Fable 5 for now because gateways not configured for Fable 5.1 reject the newer model. The release identifies selecting Fable 5.1 in /model as the available route for gateway sessions that need the newer model.