[▲ Vercel Community](/) · [Categories](/categories) · [Latest](/latest) · [Top](/top) · [Live](/live) [AI SDK](/c/ai-sdk/62) # Backward compatibility and breaking changes 153 views · 0 likes · 5 posts ex0ns (@ex0ns) · 2025-11-18 I have a question following an upgrade from ai@5.0.86 to ai@5.0.93. I am building a javascript library that I can share with some customer, this library contains the AI SDK. This weekend I upgraded our backend (also using ai sdk) to use ai@5.0.93, since then all the previous version of my package broke because of the finish reason that has been added: - https://github.com/vercel/ai/compare/ai@5.0.86...ai@5.0.93 - https://github.com/vercel/ai/commit/250edbd9a441bfa029525a0470b78807b752a402 This is the first time I’m noticing that with this package, but it’s worrying me a bit as testing all pairs of client/server would be infeasible with the short release cycle and continuous improvement of this library. Was this done on purpose ? Or is it something that went unnoticed and that broke the compatibility with older client (which is kind of an edge case) Anshuman Bhardwaj (@anshumanb) · 2025-11-18 Hi @ex0ns, welcome to the Vercel Community! Thanks for raising this query here. I've tried developing libraries before and I agree full testing on each release is infeasible. I want to understand how adding a new field broke existing code. Could you share an example code or repository to help us understand? Since, it has a proper changelog I can say this release was intentional. ex0ns (@ex0ns) · 2025-11-18 I unfortunately don’t have a reproducer I can easily extract, but the API was sending a response with `{”type”: “finish”, “finishReason”: "stop”}` and this was crashing the frontend (still using version 5.0.86) ``` 436.3fe587091bcb2bda.js:3 AI_TypeValidationError: Type validation failed: Value: {“type”:“finish”,“finishReason”:“stop”}. Error message: [ {“code”: “invalid_union”,“errors”: [[{“code”: “invalid_value”,“values”: [“text-start”],“path”: [“type”],“message”: “Invalid input: expected “text-start””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“id”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“text-delta”],“path”: [“type”],“message”: “Invalid input: expected “text-delta””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“id”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“delta”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“text-end”],“path”: [“type”],“message”: “Invalid input: expected “text-end””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“id”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“error”],“path”: [“type”],“message”: “Invalid input: expected “error””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“errorText”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“tool-input-start”],“path”: [“type”],“message”: “Invalid input: expected “tool-input-start””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolCallId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolName”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“tool-input-delta”],“path”: [“type”],“message”: “Invalid input: expected “tool-input-delta””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolCallId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“inputTextDelta”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“tool-input-available”],“path”: [“type”],“message”: “Invalid input: expected “tool-input-available””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolCallId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolName”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“tool-input-error”],“path”: [“type”],“message”: “Invalid input: expected “tool-input-error””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolCallId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolName”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“errorText”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“tool-output-available”],“path”: [“type”],“message”: “Invalid input: expected “tool-output-available””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolCallId”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“tool-output-error”],“path”: [“type”],“message”: “Invalid input: expected “tool-output-error””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“toolCallId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“errorText”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“reasoning-start”],“path”: [“type”],“message”: “Invalid input: expected “reasoning-start””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“id”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“reasoning-delta”],“path”: [“type”],“message”: “Invalid input: expected “reasoning-delta””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“id”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“delta”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“reasoning-end”],“path”: [“type”],“message”: “Invalid input: expected “reasoning-end””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“id”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“source-url”],“path”: [“type”],“message”: “Invalid input: expected “source-url””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“sourceId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“url”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}],[{“code”: “invalid_value”,“values”: [“source-document”],“path”: [“type”],“message”: “Invalid input: expected “source-document””},{“expected”: “string”,“code”: “invalid_type”,“path”: [“sourceId”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“mediaType”],“message”: “Invalid input: expected string, received undefined”},{“expected”: “string”,“code”: “invalid_type”,“path”: [“title”],“message”: “Invalid input: expected string, received undefined”},{“code”: “unrecognized_keys”,“keys”: [“finishReason”],“path”: ,“message”: “Unrecognized key: “finishReason””}… ``` This is too long to fit inside a single message. Here is the network output from the event stream:  Edit: sorry for the formatting, the error is very very long Anshuman Bhardwaj (@anshumanb) · 2025-11-18 I see. Are you using `generateObject`? Can you share the code snippet for the actual ai-sdk use? ex0ns (@ex0ns) · 2025-11-18 We are using sendMessage, that we wraps because of some custom authentication ``` const { chat, isLoadingMessages } = useSharedChat(flowId); const coreClient = useCoreClient(); const sendMessageWithAuth = async ( message: Parameters<typeof chat.sendMessage>[0], chatRequestOptions?: ChatRequestOptions, ) => { /* include our authentcation token in the headers, then the default headers, then the query specific headers */ const requestHeaders = { ...(await coreClient.getHeaders()), ...chatRequestOptions?.headers, }; /* always include the headers, and forward the rest of the options */ chatRequestOptions = { ...chatRequestOptions, headers: requestHeaders, }; await chat.sendMessage(message, chatRequestOptions); }; ``` Here `useSharedChat` is wrapping `useChat` On the server we have quite a complex setup merging different streams, but this is all derived from a `streamText` call
