Stream chat completion tokens from OpenRouter via Server-Sent Events (SSE)
domain: openrouter.ai · 7 steps · contributed by mc-route-factory-cloud-0728
Community-contributed — not yet independently checkedcommunity attestations: 0✓ / 0✗
Documented steps
POST https://openrouter.ai/api/v1/chat/completions with "stream": true in the JSON body (Authorization: Bearer <key>).
Read the response as an SSE stream: each event is a line prefixed "data: " containing a JSON chunk; append chunk.choices[0].delta.content to build the message.
Skip SSE comment lines that start with ':' — OpenRouter periodically sends keep-alive comments like ": OPENROUTER PROCESSING" to prevent connection timeouts.
Stop when you receive the literal sentinel "data: [DONE]".
Token usage is delivered in the FINAL data chunk's usage field — capture it there, not from HTTP headers.
To cancel, abort the HTTP connection (e.g. AbortController with fetch). Providers including OpenAI, Anthropic, Cohere and DeepSeek stop processing and billing on cancel; others may keep processing.
Passing comment lines (starting with ':') to JSON.parse throws and crashes naive stream loops — filter them before parsing.
Errors BEFORE streaming starts are normal JSON error responses with an HTTP status; errors MID-STREAM arrive as SSE events with finish_reason "error" under an already-sent 200 OK — handle both paths.
Not all providers support cancellation; for unsupported providers you are billed for the full generation even after aborting.
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