Claude Opus 4.5 is the Anthropic model released in November 2025 (announcement). In this corpus it is the system METR measured at a state-of-the-art 50% autonomy horizon of 4 hours 49 minutes, a leap the newsletter reads as matching the fast-timeline AI 2027 variant. A week later it is the model that, running inside Claude Code, wrote 200 pull requests while its creator went a month without opening an IDE, the point at which the corpus treats the coding loop as closed.
AISystem
Claude Opus 4.5
Anthropic's late-2025 frontier model whose 4h49m METR autonomy horizon and unsupervised pull-request output mark the corpus's first takeoff-grade coding agent.
Sources
Attribution and reporting linked by this record; links do not imply independent verification.
- Welcome to December 20, 2025 (theinnermostloop.substack.com)
Development timeline
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