Claude Code v2.1.316 release notes · Anthropic · GitHub, released the evening of October 30, 2026
Claude Code 2.1.316 deprecates Opus 4.8 fast mode, with removal on November 30
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The release notes state that fast mode for Opus 4.8 is deprecated as of October 30, 2026 and will be removed on November 30, 2026. After removal, fast mode requests on Opus 4.8 return an error and do not fall back to standard Opus 4.8. The notes say to migrate to Opus 5.5 to keep the speedup. The same release adds CLAUDE_CODE_SUBAGENT_EFFORT, which sets the effort level subagents run at when nothing else names one, instead of inheriting the session's.
Why it matters: An unattended job that pins fast mode on Opus 4.8 will stop working on November 30 rather than slow down, so search your configs and scheduled runs for it now. The new subagent effort variable gives you a direct lever on what delegated work costs.