Claude Code Fast Mode Upgrades to Opus 4.7 by Default
Claude CodeClaude Code v2.1.142 upgrades fast mode's default model from Claude Opus 4.6 to Claude Opus 4.7, giving all fast mode users access to the newer, more capable model at the same 2.5x speed and pricing. The change requires no configuration — existing fast mode users automatically benefit from Opus 4.7's improved reasoning and coding performance. Users who prefer to stay on Opus 4.6 can set CLAUDE_CODE_OPUS_4_6_FAST_MODE_OVERRIDE=1 to pin the previous default.
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Fast Mode's Default Model Is Now Opus 4.7
With Claude Code v2.1.142, released on May 14, 2026, Anthropic upgraded fast mode's default underlying model from Claude Opus 4.6 to Claude Opus 4.7. Fast mode — a high-speed configuration that delivers approximately 2.5x faster output token generation at a premium price — now brings the capabilities of Opus 4.7 to every user who has it enabled, without requiring any configuration changes.
What Changes for Existing Users
Users who already use fast mode via /fast will automatically receive Opus 4.7's performance improvements: enhanced coding accuracy, better reasoning, and vision capabilities. The speed multiplier and pricing tier remain unchanged — this is purely a model upgrade within the same fast mode experience.
How to Pin to Opus 4.6 if Needed
Anthropic provided an escape hatch for users who wish to remain on the previous model. Setting the environment variable CLAUDE_CODE_OPUS_4_6_FAST_MODE_OVERRIDE=1 pins fast mode back to Opus 4.6. This may be useful in workflows that have been tuned specifically for Opus 4.6 behavior or in enterprise environments where consistency across teams matters more than the latest model updates.
Context: Fast Mode and Opus 4.7
Fast mode first launched as a research preview for Opus 4.6, offering developers a way to trade token cost for latency in interactive workflows — rapid iteration, live debugging, and quick back-and-forth exchanges. The decision to default fast mode to Opus 4.7 reflects Anthropic's confidence in the newer model's production readiness and signals that Opus 4.7 is now the primary development target for the Claude Code toolchain.