Claude Opus 4.6 Fast

• 🏢 Anthropic's speed-optimized variant of the Opus 4.6 reasoning model
• 📏 One-million-token context window for long sessions and codebases
• ⚡ Lower-latency "fast mode" trading some depth for speed
• 🧠 Adaptive thinking with selectable reasoning effort levels
• 👁️ Multimodal: text plus vision, with function calling and web search
• 🔧 Built for agentic coding, long-horizon tasks, context compaction
• 📚 Reported 90.2% on Anthropic's BigLaw Bench legal benchmark
• 🆕 Released April 2026, between Opus 4.5 and later 4.7/4.8 lines

Anthropic

Anthropic PBC is an American artificial intelligence company headquartered in San Francisco. Structured as a public benefit corporation, the lab develops large language models under the Claude name, with a research emphasis on building reliable, steerable,…

Claude Opus 4.6 Fast is a latency-optimized configuration of Anthropic's Claude Opus 4.6, the top tier of the Claude family above the Sonnet and Haiku lines. It runs the same underlying model through a "fast mode" path, keeping the headline capabilities — a one-million-token context window (in beta), up to 128K output tokens, adaptive thinking, and context compaction — while targeting lower latency for interactive and agentic use. Capabilities here span reasoning, vision, code-optimized work, function calling, and web search.

Compared with its same-family predecessor Claude Opus 4.5, Anthropic positions Opus 4.6 as a meaningful step in long-context performance and deeper reasoning; partners noted it "thinks longer" and handles careful exploration like debugging better than Opus 4.5. On Anthropic's own BigLaw Bench it reportedly scored 90.2%, the highest of any Claude model at release, and the ARC Prize Foundation reported 94.00% on ARC-AGI-1.

The standard, full-quality version is Claude Opus 4.6; this Fast variant prioritizes responsiveness over maximum deliberation, so very hard reasoning tasks may still favor the full model.

Within the speed-optimized lineage, Opus 4.6 Fast is the earliest entry, later followed by Claude Opus 4.7 Fast and Claude Opus 4.8 Fast. Anthropic's documentation recommends the newer Opus generations for the most complex, long-horizon agentic work.