API deprecation used to mean an endpoint would change shape. For AI models it means the thing that answers your requests stops existing. OpenAI's deprecations page lists about fifty model snapshots with a shutdown date between September 24 and December 11, 2026, GPT-4 among them. Anthropic retired nine Claude models in twelve months. This is how model deprecation works under the hood: the lifecycle, what breaks in your code on the morning after, what "weights preservation" actually preserves, an...