On 2026-10-15 Anthropic moved Claude Opus 5.5 fast mode out of research preview and removed the waitlist: no access request and no fast-mode-2026-02-01 beta header needed, just speed: "fast". Same weights, up to 2.5x output tokens/sec per Anthropic, at 2x standard price ($8/$40 per MTok). Start/Build/Scale tiers get a default fast rate limit; it is live on Microsoft Foundry (Azure-hosted) with Google Cloud coming soon. Opus 5 and Opus 4.8 fast mode remain in research preview.

Key Takeaways

  • ✓Pricing: Opus 5.5 fast is $8/$40 per MTok, 2x the $4/$20 standard; Opus 5/4.8 fast stay in preview at $10/$50 (docs)
  • ✓Speed: up to 2.5x output tokens/sec per Anthropic; gains are OTPS, not TTFT; same weights
  • ✓Access: no request and no beta header; default dedicated fast limits on Start/Build/Scale tiers (release notes)
  • ✓Platforms: Claude API (incl. Managed Agents) and Microsoft Foundry Azure-hosted; Google Cloud coming soon; not on Batch API, Priority Tier, or Claude Platform on AWS
  • ✓Gotchas: switching speeds invalidates the prompt cache; 429 on limit; check usage.speed
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🛠️ Ecosystem & IDERules
Anthropic · Claude Opus 5.5 · fast mode
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Project Links & Resources

Direct Access
Direct access to official project resources and documentation
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Claude Docs: Fast mode
platform.claude.com/docs/en/build-with-claude/fast-mode
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Claude Platform release notes (2026-10-15)
platform.claude.com/docs/en/release-notes/overview
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In-Depth Technical Analysis

Core Background & Industry Pain Points

For long-running coding agents, output speed often decides how long each loop takes. Anthropic's fast mode launched as a waitlisted research preview on Opus 4.6 in February 2026 and arrived on Opus 5.5 (Sept 22) still as a preview. On 2026-10-15 the Claude Platform release notes moved Opus 5.5 fast mode out of research preview and removed the access request.

Architecture Highlights & Internals

Per the fast mode docs, it is the same model weights on a faster inference configuration. Gains target output tokens per second (OTPS), not time to first token. Fast mode has a dedicated rate limit (429 + retry-after, anthropic-fast-* headers), and usage.speed reports whether a request ran fast or standard.

Authoritative Benchmarks & Measured Scores

Anthropic says "up to 2.5x" OTPS; no independent speed measurements are public yet. Pricing: Opus 5.5 fast is $8/$40 per MTok, 2x the $4/$20 standard rate; Opus 5 / Opus 4.8 fast stay in research preview at $10/$50. The multiplier applies across the full context window and stacks with caching and data-residency multipliers.

Developer Hands-on Guide

Send "speed": "fast"; the fast-mode-2026-02-01 beta header is no longer required for Opus 5.5 (still accepted). Start/Build/Scale tiers get a default fast limit; Evaluation tier must upgrade. Available on Microsoft Foundry (Azure-hosted deployments), Google Cloud "coming soon"; not on Batch API, Priority Tier, or Claude Platform on AWS. Switching speeds invalidates the prompt cache, so pick one speed per workload and add a 429 fallback to standard speed.

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