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Fast mode research preview available for Claude Opus 5.5 on the Claude API

Tech · Releases · Tue, September 22, 2026

Source

Fast mode, in research preview, can now be used with Claude Opus 5.5 on the Claude API.

Every year

DateEventWhen
Jun 30, 2026Claude Sonnet 5 launches with a 1M token context window at $2 / $10 per MTok3 mo ago
Jul 2, 2026agent-memory-2026-07-22 beta header changes memory store listing behavior3 mo ago
Jul 10, 2026Dreams research preview adds Claude Fable 5 and Claude Sonnet 53 mo ago
Jul 14, 2026Admin API adds Claude Enterprise user management in beta2 mo ago
Jul 15, 2026Mid-conversation system messages available on Claude Fable 5, Mythos 5 and Opus 4.82 mo ago
Jul 22, 2026Claude Managed Agents agents accept an effort level in model configuration2 mo ago
Jul 24, 2026Claude Opus 5 launches with a 1M token context window at $5 / $25 per MTok2 mo ago
Jul 24, 2026Claude API fallbacks parameter adds a default mode for recommended fallbacks2 mo ago
Jul 24, 2026Mid-conversation tool changes enter beta on the Claude API2 mo ago
Aug 1, 2026Dreams research preview adds support for Claude Opus 52 mo ago
Aug 3, 2026Compliance API returns cloud Cowork session transcripts in beta2 mo ago
Aug 5, 2026Inference hooks2 mo ago
Aug 7, 2026Claude Managed Agents sessions can consult an advisor model2 mo ago
Aug 19, 2026Agent Skills and the Skills API are out of beta on the Claude API37 days ago
Aug 19, 2026Claude Enterprise Admin API user-management endpoints are out of beta37 days ago
Aug 19, 2026Files API is out of beta on the Claude API37 days ago
Aug 19, 2026Claude computer use tool is out of beta as computer_toolset_2026080137 days ago
Aug 19, 2026Claude API launches browser_toolset_20260801 browser use tool37 days ago
Aug 26, 2026Admin API comes to the ant CLI and Claude SDKs under client.beta.organization30 days ago
Aug 26, 2026Compliance API adds Claude Science and Microsoft 365 session transcripts in beta30 days ago
Sep 1, 2026Claude Fable 5.1 launches alongside Claude Mythos 5.1 with 1M token context24 days ago
Sep 1, 2026Claude API adds turn-scoped system messages in beta24 days ago
Sep 1, 2026Claude API thinking.display adds an updates mode in beta24 days ago
Sep 1, 2026Per-message effort changes enter beta on the Claude API24 days ago
Sep 1, 2026Claude Fable 5.1 thinking blocks only replay to the same or newer models24 days ago
Sep 3, 2026Per-message effort changes beta expands to Claude on Google Cloud22 days ago
Sep 10, 2026ant CLI 1.32.0 adds sessions connect for live Managed Agents sessions15 days ago
Sep 14, 2026Claude API input_transformations adds thinking_mismatch_allowed entries in beta11 days ago
Sep 14, 2026Messages API adds on-demand conversation compaction in beta11 days ago
Sep 18, 2026Compliance API adds Claude in Chrome session transcripts in beta7 days ago
Sep 18, 2026For cache diagnostics, a response to a request that sends the cache-diagnosis-2026-04-07 beta header now7 days ago
Sep 22, 2026Claude Opus 5.5 launches with a 1M token context window and 128k output3 days ago
Sep 22, 2026Claude API beta lets tools be defined inside mid-conversation system messages3 days ago
Sep 22, 2026Fast mode research preview available for Claude Opus 5.5 on the Claude API3 days ago
Sep 23, 2026Cache diagnostics is out of beta on the Claude API and no longer requires the cache-diagnosis-2026-04-07 beta2 days ago

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anthropic
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anthropic
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Changes
  • 2026-09-25: added to 2026-09-22

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