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Monday 1 June — v2.1.159
1 change / 1 actionable / 1 deep dive
Claude Code

TL;DR

  • CLAUDE_CODE_OPUS_4_6_FAST_MODE_OVERRIDE removal deadline is today. Deprecated in 2.1.154 with a June 1 removal date, so if you still set it, switch to /model claude-opus-4-6[1m] then /fast on instead (more below).
  • Nothing else actionable in 2.1.159. Internal infrastructure only, no user-facing changes.

New in 2.1.159

2.1.159 (June 1, 2026)

  • Internal infrastructure improvements (no user-facing changes)

Notes

Opus 4.6 fast mode env var

2.1.154 (May 29) deprecated CLAUDE_CODE_OPUS_4_6_FAST_MODE_OVERRIDE and announced removal on June 1. Today is that date. The replacement path: switch to the Opus 4.6 1M model with /model claude-opus-4-6[1m], then enable fast mode with /fast on. If you have the env var in shell profiles, dotfiles, or CI configs, clean it out to avoid silent failures when a future version drops the variable entirely.