Streaming - OrcaRouter
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Set stream: true to receive incremental tokens as Server-Sent Events instead of one final response. Latency-to-first-token drops to a single network round-trip.

OpenAI-compatible (Chat / Responses)

Each line is data: {...}. Stream ends with data: [DONE]. To get the final usage object inside the stream, pass stream_options: { include_usage: true } — the chunk just before [DONE] will include token counts.

Anthropic Messages

Anthropic uses named SSE events. On OrcaRouter’s first-class Anthropic surface, the full set Anthropic emits comes through directly:
Each event is followed by a data: {...} JSON line.

Errors during a stream

Errors emitted mid-stream cannot use HTTP status codes (the status was sent when the stream opened). See Operations / Errors for the in-band error shapes.

Streaming and fallback

Once any byte of the response has been sent to the client, OrcaRouter can no longer fall back to the next chain entry — see the streaming caveat in Model Fallbacks.

Next steps

Tool calling

Stream tool-call deltas as they arrive.

Errors

Handle mid-stream failures.