Simon Willison Analyzes Anthropic's Claude System Prompt Evolution Using Git Timeline Method

Simon Willison created a method to track changes in Anthropic's Claude AI system prompts by converting them into a git timeline format. On April 18, 2026, Willison published an analysis detailing his process of extracting system prompts from Anthropic's public documentation. He transformed the Markdown page containing Claude's system prompts into separate files organized by model and model family, assigning artificial git commit dates to enable chronological browsing through GitHub's commit view interface. This technical approach allowed Willison to conduct a detailed comparative study between Claude Opus versions 4.6 and 4.7, examining the specific modifications made to the AI's underlying instructions. The project demonstrates a novel application of version control systems for analyzing AI development patterns. Willison's work provides transparency into how Anthropic evolves its AI models through prompt adjustments. The analysis was shared on his personal website alongside an invitation for sponsorship, offering subscribers a monthly curated digest of significant large language model developments for $10 per month.