Claude Opus 5.5 is an Anthropic model released in September 2026 for long-running coding, agent and knowledge work, and the first of its Claude 5.5 family.
In plain words
Anthropic sells several Claude models at different sizes. Opus 5.5 sits one step below its Fable models. At launch Anthropic said it matched Claude Fable 5.1 on most tasks while being cheaper to run than Opus 5. Its docs suggest starting with Opus 5.5 for most workloads and moving up to Fable 5.2 when a task needs deeper reasoning or Opus falls short. It can hold 1 million tokens of context and is available in the Claude apps and through the API and major clouds.
A quick example
Imagine a team handing Opus 5.5 a slow web app and asking it to speed up every page. Anthropic reports that in one such test, Opus 5.5 succeeded 39 times out of 40.
Where you'll meet it
- Long coding and agent tasks, in Claude Code or through the API.
- Professional knowledge work in the Claude apps.
Related
Sources
- DocsIntroducing Claude Opus 5.5, Anthropic · read 29 Sept 2026
- DocsModels overview, Claude Docs (Anthropic) · read 9 Nov 2026
- DocsClaude Opus, Anthropic · read 29 Sept 2026
- DocsClaude Fable 5.2 and Claude Mythos 5.2, Anthropic · read 9 Nov 2026
Checked by WhatIsAI against the sources above · 9 Nov 2026. Spotted an error? Report it.