report · 2026-09-22
Claude Opus 5.5 System Card
Anthropic
Why it matters here
CoBench 2.1 contextualizes internal R&D capability through historical issue diagnosis and explicitly warns about environment drift.
AI-R&D capability
What to keep in mind
- Environment changed between versions; scores are not comparable across versions.
- Private historical infrastructure and model-graded root-cause rubrics limit external replication.