Streaming API

How to enable streaming

Add stream: true to a normal Messages API request. The server returns a Server-Sent Events stream instead of one JSON response.

{
  "model": "claude-sonnet-4-6",
  "max_tokens": 512,
  "stream": true,
  "messages": [
    {"role": "user", "content": "Explain SSE in one paragraph"}
  ]
}

Streaming with SDKs and cURL

Anthropic SDKs parse SSE and expose a convenient text stream. With direct HTTP, cURL shows the raw event and data lines.

curl https://api.llm-gate.tech/v1/messages \  --header "x-api-key: $CLAUDE_API_KEY" \  --header "anthropic-version: 2023-06-01" \  --header "content-type: application/json" \  --no-buffer \  --data '{    "model": "claude-sonnet-4-6",    "max_tokens": 512,    "stream": true,    "messages": [      {"role": "user", "content": "Explain SSE in one paragraph"}    ]  }'

SSE event sequence

Each stream begins with message_start, contains one or more content blocks, and ends with message_stop. Ping events may appear in between.

• message_start — a Message object with an empty content array.
• content_block_start — the start of a text, tool_use, or thinking block.
• content_block_delta — the next incremental update for the block.
• content_block_stop — the block has finished.
• message_delta — stop_reason and cumulative usage updates.
• message_stop — the stream completed successfully.

Full HTTP stream response

For a direct HTTP integration, read SSE lines in order. The event field names the event, while data contains JSON with the matching type.

event: message_start
data: {"type":"message_start","message":{"id":"msg_...","content":[]}}

event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}

event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"Hello"}}

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":8}}

event: message_stop
data: {"type":"message_stop"}

Main delta types

When the response is complete

Do not stop after the first text or content_block_stop event. The complete response is ready only after message_stop. Usage values in message_delta are cumulative.

• Accumulate blocks by index; it matches the block's position in the final content array.
• Ignore ping and unknown future event types without crashing the parser.
• For a final Message object, use finalMessage() in TypeScript or get_final_message() in Python.

event: error
data: {
  "type": "error",
  "error": {
    "type": "overloaded_error",
    "message": "Overloaded"
  }
}