Anthropic appears to be quietly testing a new model, with users reporting Claude Opus 5.5 routing to a new checkpoint that delivers superior output.

• Anthropic is quietly testing a new model, with some Claude Opus 5.5 traffic being routed to a new checkpoint. testingcatalog
• Users have identified a method to detect the new model by asking Opus 5.5 about VoxelBench. testingcatalog
• Some users speculate the new model could be a fresh Opus 5.5 checkpoint or Opus 5.6. testingcatalog