Claude Code v2.1.86 Released - Session ID Header and VCS Exclusion Improvements

Anthropic has released Claude Code v2.1.86. This update includes session management improvements, expanded VCS exclusions, and numerous bug fixes and performance enhancements.

Key Changes

Session Management and Proxy Support

• X-Claude-Code-Session-Id Header: Added session ID header to API requests, enabling proxies to aggregate requests without parsing the request body

VCS Exclusion Extensions

• .jj and .sl Additions: Added Jujutsu (.jj) and Sapling (.sl) metadata directories to VCS exclusion lists, preventing Grep and file autocomplete from descending into these directories

Performance and Stability Improvements

• Reduced startup event-loop stalls when many claude.ai MCP connectors are configured
• Improved @-mention file autocomplete performance on large repositories
• Improved scroll performance with large transcripts by replacing WASM yoga-layout with a pure TypeScript implementation
• Reduced token overhead when mentioning files with @ — raw string content no longer JSON-escaped

Tools and Configuration Fixes

• Fixed —resume failing with “tool_use ids were found without tool_result blocks” on sessions created before v2.1.85
• Fixed Write/Edit/Read failing on files outside the project root (e.g., ~/.claude/CLAUDE.md) when conditional skills or rules are configured
• Fixed unnecessary config disk writes on every skill invocation that could cause performance issues and config corruption on Windows
• Fixed potential out-of-memory crash when using /feedback on very long sessions
• Fixed —bare mode dropping MCP tools in interactive sessions

VS Code Extension Improvements

• Fixed extension incorrectly showing “Not responding” during long-running operations
• Fixed extension defaulting Max plan users to Sonnet after OAuth token refreshes (8 hours after login)

Other Changes

• Skill descriptions now capped at 250 characters to reduce context usage
• /skills menu now sorted alphabetically for easier scanning
• Read tool now uses compact line-number format and deduplicates unchanged re-reads
• Improved prompt cache hit rate for Bedrock, Vertex, and Foundry users

v2.1.86 demonstrates continued evolution of Claude Code with steady improvements and stability enhancements.