Frontier flagship models
Claude Opus 5.5
Made by Anthropic
Anthropic's model for long-running agentic coding and knowledge work — released September 2026.
What it is
Claude Opus 5.5 is the first release in Anthropic's Claude 5.5 family, built for long-running agentic coding and knowledge work. It succeeds Claude Opus 5 and is reached through Claude paid plans (Pro, Max) and the Anthropic API.
Anthropic's launch post reports that Opus 5.5 matches Claude Fable 5.1 on most work at 40% lower running cost than Opus 5, and that it is the strongest model to date on the lab's automated behavioral audit. Those are the maker's own figures; check independent leaderboards for a specific task.
It is the first Anthropic release since the lab called for pacing the frontier, and was tested before release by external evaluators including Frontier Design and METR, per the announcement.
Heavier Opus 5.5 access needs a paid Claude plan; the free plan applies a rolling usage window.
Published price
- API — input$4 per 1M tokens
- API — output$20 per 1M tokens
- API — cache writes (5 min / 1 hour)$5 / $8 per 1M tokens
- API — cache hits$0.20 per 1M tokens
- Claude FreeChat on web, desktop and mobile; usage-window limits apply$0
- Claude Pro$17/month (annual) or $20/month
- Claude MaxFrom $100/month
Consumer plan prices are for Claude.ai overall; model access on each plan follows usage limits rather than a fixed assignment.
Source: Anthropic's pricing page · Last checked 27 September 2026
Benchmarks
The published figures for Claude Opus 5.5, copied exactly as their sources give them and checked 17 September 2026. Each one names the test, who ran it and when, and says when the number comes from the maker rather than an independent tester.
- Artificial Analysis Intelligence Index v4.3.258 — 1st of 216 models
combined score across ten reasoning and knowledge tests · tested: max with fallback
Artificial Analysis · 28 September 2026 · independent
Measured at 95.2 tokens per second output speed.
Figures copied from the sources above, checked 17 September 2026.
Where to read today's numbers
Scores move, so these are the boards that keep them current.
- LMArena leaderboardIndependent
Ranks models by blind head-to-head votes from the public. Good for a feel for general quality, weak on specialist work.
- Artificial AnalysisIndependent
Independent testing of quality, speed and price per million tokens across hosted models.
- Vals AI benchmarksIndependent
Independent evaluations on real professional tasks — law, finance, tax, medicine — rather than vendor demos.
How it performs, in my experience
Anthropic's model for long-running agentic coding and knowledge work, and the first release since the lab called for pacing the frontier. Its launch post reports it matches Claude Fable 5.1 on most work at 40% lower running cost than Opus 5; benchmark figures are the maker's own, so check independent leaderboards for a specific task.
Prompting it from this site
Can't be run from here
This site has no Claude wired up — the models it prompts run through OpenAI's and Google's endpoints. Use Claude.ai or Anthropic's API instead.
Use it for
- Long-running coding and migration tasks
- Knowledge-work and document reasoning
- Agentic workflows through Claude paid plans