Streaming · Anthropic format
Event sequence for /v1/messages
/v1/messages with stream: true emits this event sequence regardless of which upstream provider served the request:
event: message_start
data: {"type":"message_start","message":{...}}
event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}
# one per delta:
event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"..."}}
event: content_block_stop
data: {"type":"content_block_stop","index":0}
event: message_delta
data: {"type":"message_delta","delta":{"stop_reason":"end_turn"},"usage":{"output_tokens":N}}
event: message_stop
data: {"type":"message_stop"}stop_reason maps from the provider: stop → end_turn, length → max_tokens.