Summary of METR's predeployment evaluation of Claude Opus 5.5

Note on independence: This evaluation was conducted under an unpaid agreement for AI R&D assessment.1 We drafted the initial summary, and then Anthropic had the opportunity to review and edit the text. We signed off on this final text from the Claude Opus 5.5 system card. Our preliminary evaluation focused on how Claude Opus 5.5 might impact AI R&D, mainly based on its capabilities on difficult, long-horizon tasks. The main claims we attempt to assess in this report are: (A) would AI R&D at Anthropic now be dramatically accelerated by using Claude Opus 5.5; and (B) was AI R&D at Anthropic already dramatically accelerated due to AI during the development of Claude Opus 5.5. Note that our work was oriented around collecting evidence related to AI R&D capabilities but was not meant to verify claims about compliance with any specific threshold from Anthropic’s policies. This report summary also does not attempt to assess…