Anthropic used Claude Code to drive large-scale internal code migrations—the kind of tedious, repetitive refactors (API version bumps, dependency upgrades, framework moves) that normally eat engineer-weeks—by letting the agent do the bulk mechanical work at scale rather than one file at a time. The practical takeaway: migrations are now a viable agentic workload if you invest in scoping, verification harnesses, and human review gates, since the bottleneck shifts from writing changes to validating and catching the agent's mistakes across thousands of files.