What changed

Anthropic retired `claude-sonnet-4-20250514` and `claude-opus-4-20250514` from its first-party Claude API. Requests to either exact model ID now fail, requiring affected production workloads to move to supported successors and revalidate behavior.

Why it matters

Both IDs can remain embedded in gateways, jobs, fixtures, and fallback chains, creating hard failures at a first-party API boundary.

What to do

Search every call path for both IDs, migrate explicitly, and replay contract, tool-loop, structured-output, context, latency, safety, cost, fallback, and rollback tests before full traffic transfer.

Caveat

The cutoff applies to Anthropic's first-party API. Amazon Bedrock and other hosts have separate lifecycles, approved researchers can receive exceptions, and successor equivalence is unproven.