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Anthropic · Shipped

Claude Sonnet 5.5 release date

What we forecast

First forecast on Sep 14, 2026: Oct 14, 2026. Last forecast before launch, on Sep 27, 2026: Sep 28, 2026. It shipped that day.

Specs, benchmarks and changelog are on the Claude Sonnet 5.5 model card at TPS.

Released

Sep 28, 2026

What we know

A clear upgrade over Sonnet 5 that runs 30% faster and costs up to 30% less for most work.

Spec

Params
Not stated
Active
Not stated
Context
1000000
Weights
Closed
Modality
Not stated
Codename
Not stated

Every claim

12 from 8 sources
  • TestingCatalogFrom the labSep 29

    Anthropic launched Claude Sonnet 5.5 with faster output, lower costs, and improved coding capabilities.

    no date givenno datesource
  • OpenRouter catalogSpotted in the wildSep 28

    Claude Sonnet 5.5 is available on OpenRouter as a direct upgrade to Claude Sonnet 5, with 1M token context window.

    no date givenno datesource
  • The DecoderSpotted in the wildSep 28

    Anthropic released Claude Sonnet 5.5, the second model in its Claude 5.5 family, with 30% faster output and lower costs.

    points at Sep 28exact datesource
  • TechCrunch AIFrom the labSep 28

    Anthropic released Claude Sonnet 5.5, a mid-range model with faster response times and reduced token usage.

    points at Sep 28exact datesource
  • Simon WillisonFrom the labSep 28

    Claude Sonnet 5.5 released by Anthropic, 30% faster and 30% cheaper than Sonnet 5, now powers free tier of claude.ai.

    points at Sep 28exact datesource
  • OpenRouter catalogSpotted in the wildSep 28

    Claude Sonnet 5.5 is available on OpenRouter as a routable model with 1M token context window.

    no date givenno datesource
  • TechmemeFrom the labSep 28

    Anthropic released Claude Sonnet 5.5, 30% faster and 30% cheaper than Sonnet 5.

    points at Sep 28exact datesource
  • Anthropic NewsFrom the labSep 28

    Claude Sonnet 5.5 released, running 30% faster and costing up to 30% less than Sonnet 5.

    points at Sep 28exact datesource
  • Simon WillisonSpotted in the wildSep 28

    Claude Sonnet 5.5 is now supported in llm-anthropic plugin version 0.30.

    points at Sep 28exact datesource
  • TestingCatalogInsiderSep 27

    Claude Sonnet 5.5 could launch within the following week based on leaked partner checkpoint tests.

    points at Oct 4weeksource
  • The DecoderFrom the labSep 22

    Anthropic says Sonnet 5.5 is expected in the coming weeks.

    points at Oct 22monthsource
  • PolymarketBetting marketSep 14

    Polymarket, “Next Claude Sonnet released by...?”: 90% by Sep 28, 97% by Sep 29, 99% by Sep 30, 99% by Oct 15. $69K traded.

    no date givenno datesource
Official announcement