SSE protocol catalog
Streaming shapes for OpenAI Chat, Responses, Anthropic Messages, and Gemini alt=sse — and what the gateway does on passthrough vs translate.
Gateway streaming by dialect. Same-family traffic is byte-passthrough after model rewrite; cross-dialect rebuilds events from the canonical IR.
OpenAI Chat Completions
| Data |
Notes |
choices[].delta |
Token deltas; role on first chunk |
delta.reasoning_content |
Thinking on openai_compat (DeepSeek/Kimi/…) |
delta.tool_calls |
Incremental tool args |
finish_reason |
On final choice chunk |
data: [DONE] |
Terminator |
stream_options.include_usage |
Gateway forces usage metering on translate/build when streaming |
OpenAI Responses API
| Event |
Notes |
response.created / in_progress / completed |
Lifecycle |
response.output_text.delta |
Text |
response.function_call_arguments.delta |
Tools |
| Passthrough |
openai family does not rewrite SSE |
Experimental duplex: Realtime WebSocket → GET /v1/responses/ws.
Anthropic Messages
type |
Notes |
message_start |
Skeleton + usage start |
content_block_start / delta / stop |
Text, tool_use, thinking |
message_delta |
stop_reason, tokens |
message_stop |
End |
ping |
Keepalive (forwarded on passthrough) |
Google Gemini (alt=sse)
| Shape |
Notes |
JSON per data: line |
candidates[].content.parts[] |
thought: true |
Thinking; thoughtSignature preserved for multi-turn |
functionCall |
Tool use |
Final usageMetadata |
Mapped when present |
Policy
- Passthrough: do not strip unknown event types or fields.
- Translate: rebuild only known IR fields; do not invent vendor events.
- Client disconnect mid-stream → usage status
client_abort.
