Why is my LLM stream empty? A field guide to broken SSE responses
If you have ever called an OpenAI-compatible API with streaming enabled and received... nothing, you are not alone. No error, no exception — just a stream that "completes" successfully while your UI stays empty. After debugging dozens of these cases — and building an open-source toolkit to automate the diagnosis — I keep seeing the same four failure modes. Here is the field guide I wish I had. 1. Reasoning-only responses Some models emit their entire answer inside a reasoning channel (the "thinking" part) and mark the actual channel as empty. The stream works. Token usage is reported. Your parser is happy. Your UI shows nothing.
If you have ever called an OpenAI-compatible API with streaming enabled and received... nothing, you are not alone. No error, no exception — just a stream that "completes" successfully while your UI stays empty. After debugging dozens of these cases — and building an open-source toolkit to automate the diagnosis — I keep seeing the same four failure modes. Here is the field guide I wish I had. 1. Reasoning-only responses Some models emit their entire answer inside a reasoning channel (the "thinking" part) and mark the actual channel as empty. The stream works. Token usage is reported. Your parser is happy. Your UI shows nothing.