Breaking changes for AI SDK 4.0: baseUrl→baseURL, remove await from streamText/streamObject, maxToolRoundtrips→maxSteps, experimental exports removed, facade constructors removed, type renames (ExperimentalMessage→ModelMessage), method renames (toAIStream→toDataStream), property renames (rawResponse→response, roundtrips→steps), warnings becomes Promise, UI hooks streamMode→streamProtocol, framework imports split to separate packages, error methods isXXXError→isInstance.