Run large migrations as a six-step loop where you fix the rulebook, never the file

Claude by Anthropic·high signal

Anthropic published its internal methodology for Claude Code migrations (Jul 16, 2026): build a rulebook + dependency map + gap inventory, stress-test rules on 3 throwaway sample files, translate in parallel with small models, compile, smoke test, verify against the existing test suite. The governing rule is that every systemic failure gets fixed upstream in the rulebook rather than hand-patched in the generated file. Receipts: Bun's Zig→Rust migration hit ~1M lines in under two weeks (~$165K) with 100% of the existing suite green before merge; a 165K-line Python→TypeScript port took one weekend and 27M tokens.