1Claude Opus 5.5
No. 1 — Claude Opus 5.5. On the lists of 8 of 10 AIs; median place there: 1. It is the best model anyone can open today: first for building web apps and on Agent Arena, and only one index point behind Carbon.
Did you know
Opus 5.5 is the first model in Anthropic's Claude 5.5 family. Anthropic says it does most tasks at the level of Claude Fable 5.1 while costing 40% less to run than Opus 5.
- What it is
- Anthropic's newest top model, open to everyone in Claude apps and the API.
- Its edge
- Open to the public, and #1 on WebDev, while Carbon is locked.
- Who it suits
- Suits people who want top results today and can pay; heavy max-effort use burns quota fast.
- AA Intelligence Index score58 on the index
Why it is here
On Artificial Analysis's Intelligence Index, Claude Opus 5.5 scored 58 at max effort, ranked first in that report. The older Claude Opus 5 scored 51, so it gained seven points in one release.
Opus 5.5 costs $4 per million input tokens and $20 per million output tokens, down from Opus 5's $5 and $25. It used about 119k output tokens per index task, at roughly $6 a task.
History
On 22 Sept 2026 Anthropic released Claude Opus 5.5, ending outside guessing about whether it would come. It costs 20% less per token than Opus 5 and uses less compute.
Keep in mind
Max effort mode uses "6x or more" of your usage, says the Claude app. Anthropic gives no fixed number, and users report 4x, 5.5x and 6x. Some users also expect the model to get weaker after launch.
In one same-task test, a user found Opus 5.5 made poor design choices for a feature, and the model agreed they were weak. Fable 5.1 did better on that task. It also has a biology safety filter.
What people say
The way Opus 5.5 communicates is genuinely an order of magnitude improvement over Opus 5. — u/mdspan (Reddit)
Where to go further
Read Anthropic's announcement page first, then try Opus 5.5 in the Claude apps or Claude Code. Start with a real coding task, such as fixing a small bug in your own project, and compare the result with what you use now.