ChatGPT, Claude, Gemini: the AI you pay for keeps changing

AI subscriptions sell an artifact and deliver a service: the vendor keeps control of which model answers, how much of it you get, and how it is served, so quality can change after you subscribe without anything being announced. The four failure modes: silent model retirement, allowance erosion at a constant price, identical weights scoring differently by provider, and retention rules changing under your data, plus what to watch instead of release notes.