Claude system prompts restructured into a git timeline for prompt archaeology

Simon Willison converted Anthropic’s published Claude system prompt history—originally a single markdown page—into a git repository with per-model, per-family files and backdated commits. The restructuring turns an opaque monolith into something navigable with standard tooling: git log surfaces the revision timeline, diff exposes what changed between versions, and blame attributes specific language to specific releases.

The practical payoff is prompt archaeology at scale. Instead of manually parsing a sprawling markdown file to spot drift between model generations, researchers can diff Opus 4.6 against 4.7 directly. Willison used exactly this setup to produce his own line-by-line notes on what Anthropic changed between those two releases, treating the system prompt as versioned infrastructure rather than a static document.

The underlying insight is that system prompts have become production artifacts worth tracking like code. As frontier labs iterate on prompt scaffolding—safety instructions, tool-use guidance, personality tuning—the delta between versions is often where the behavioral shifts actually live, and git is the natural substrate for auditing that evolution.