How to Stream LLM Tokens in PHP Using Server-Sent Events

Developers building chat interfaces in PHP can eliminate the blank-screen wait by streaming large language model (LLM) tokens incrementally using Server-Sent Events (SSE). The NanoAgent library's Agent::stream() method delivers each token via a callback, which the developer formats as an SSE data line and immediately flushes to the browser. Four specific HTTP headers are required to convert a standard PHP response into a persistent SSE stream, with the X-Accel-Buffering header being critical for Nginx environments that buffer upstream responses by default. On the client side, a native browser EventSource object handles incoming tokens without any additional libraries, appending each token to the UI until a [DONE] sentinel signals the end of the stream. Compared to WebSockets, SSE is simpler for one-way token delivery since it runs over plain HTTP and supports automatic reconnection.