CoBench (Anthropic)
Claude Opus 5.5 55.8% Only in system cards
500 real internal Anthropic R&D problems. Percentage solved in one attempt tracks AI R&D acceleration.
v2.1 scores not comparable with earlier CoBench versions.
Made by Anthropic Labs' internal R&D tests Tasks kept private Last in a system card Sep 2026
Last model added Sep 2026
- Level
- Expert Specialists with years of training, often over hours of work
- Scored
- Graded by a model A language model scores each response, usually against a rubric.
- Answers
- Agent task Many steps in a terminal, browser, desktop, app, game or robot.
1
Model scored in lab cards
1
System card reports it, from 1 lab
Claude Opus 5.5 leads with 55.8%
Best score per model as labs report them in their own cards. Labs pick their own settings, so these compare less cleanly than independent runs.
- 1 Claude Opus 5.5 55.8%
| # | Model | Score | Setting | Date | Source |
|---|---|---|---|---|---|
| 1 | Claude Opus 5.5 | 55.8% | Sep 2026 | Model card |
Scores over time
All the scores we have, one dot each, so a model tested at several settings appears more than once.
Reported by the lab in its model card
Labs report it only in system cards
We read the headline results of 479 launch posts from 51 labs, and none of them list this benchmark. Some system cards do, below.
One system card reports it
Besides launch posts, we read the system cards, model cards and technical reports labs publish with a release. They report far more, including safety and frontier-risk tests.
| Date | Document | Score | As the document writes it | Section |
|---|---|---|---|---|
| 22 Sep 2026 | Claude Opus 5.5 system card | 55.8 | CoBench 2.1, share of 500 internal R&D problems solved in one attempt, API safety filter off. Not comparable with earlier CoBench versions (2.3.4.1, Figure 2.3.4.1.A) | AI R&D risk |
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