AI library

Source · release

Claude Code releases 2.1.299 and 2.1.300

Author
Anthropic
Published
14 October 2026
Added
15 October 2026
Original
https://github.com/anthropics/claude-code/releases/tag/v2.1.300

Summary

Two Claude Code releases on 2026-10-14 (the releases page shows "14 Oct" without a year; the 2026 date follows from the version sequence). 2.1.299 adds idle compaction, which compacts long idle conversations before their prompt cache expires, plus a large batch of MCP, sandbox, and hook fixes. 2.1.300 splits cache-write telemetry by cache lifetime and adds OpenTelemetry GenAI attributes. The 2.1.299 notes are on its own release page (/releases/tag/v2.1.299).

Key points

  • Idle compaction (2.1.299): a terminal conversation over 200K tokens left idle for about 54 minutes is compacted before its one-hour prompt cache expires, so the next message does not reprocess the full context at uncached prices. Threshold: CLAUDE_CODE_IDLE_COMPACT_MIN_TOKENS; disable with "idleCompaction": false.
  • CLAUDE_CODE_DISABLE_FILE_MENTIONS: @ mentions pass file paths for Claude to read with its tools, not the file contents.
  • MCP: cloud-session and Remote Control connectors now default to protocol 2026-07-28 (MCP_PROTOCOL_NEGOTIATION=legacy opts out). MCP allow rules now match only the named server (mcp__a no longer covers a__b); connector-proxy requests no longer follow redirects; policy-blocked servers are no longer contacted.
  • Hooks and sandbox fail closed in more cases: plugin hooks that cannot answer now block; hooks' updatedInput is validated like Claude's own input; plan mode no longer runs writes that a hook allowed; several sandbox symlink and glob escapes fixed.
  • 2.1.300: cache_creation_5m_tokens and cache_creation_1h_tokens in the OpenTelemetry api_request event; GenAI semantic-convention attributes on trace spans; /advisor on Claude Platform on AWS; large requests gzip-compressed.

Why it matters

Idle compaction is a cost optimisation built around the prompt-cache TTL: paying for a compaction is cheaper than re-reading 200K+ tokens after the cache expires. It also extends Claude Code's default use of the stateless MCP spec from local to remote connectors.