Claude Code is Anthropic’s command-line agent that runs Claude models against a codebase (product page). It enters the corpus with a tooling note, Language Server Protocol support, but within days becomes the newsletter’s central instrument of recursion: its own creator reports it wrote 200 pull requests without him, and Anthropic confirms it wrote the whole Claude Cowork desktop app in a week and a half. By March 2026 PostTrainBench v1.0 names Opus 4.6 running in Claude Code the most capable agent at automating a model’s own post-training.
AISystem
Claude Code
Anthropic's terminal coding agent, the harness through which the corpus most often watches a model write, ship and post-train software without a human in the loop.
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- Welcome to December 23, 2025 (theinnermostloop.substack.com)
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