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Claude Chat Object

Crazyrouter supports Anthropic Claude’s native Messages API format. This page describes the Message object and streaming event types.

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Message Object

The complete Message object returned by non-streaming requests: 
{
  "id": "msg_abc123",
  "type": "message",
  "role": "assistant",
  "content": [
    {
      "type": "text",
      "text": "Hello! How can I help you?"
    }
  ],
  "model": "claude-sonnet-4-20250514",
  "stop_reason": "end_turn",
  "stop_sequence": null,
  "usage": {
    "input_tokens": 15,
    "output_tokens": 20,
    "cache_creation_input_tokens": 0,
    "cache_read_input_tokens": 0
  }
}

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Field Descriptions

FieldTypeDescription
idstringUnique message identifier
typestringAlways message
rolestringAlways assistant
contentarrayList of content blocks, can contain text and tool_use types
modelstringThe model actually used
stop_reasonstringStop reason: end_turn, max_tokens, stop_sequence, tool_use
stop_sequencestring|nullThe sequence that triggered the stop
usageobjectToken usage

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content Block Types

Text block: 
{
  "type": "text",
  "text": "Response content"
}
Tool use block: 
{
  "type": "tool_use",
  "id": "toolu_abc123",
  "name": "get_weather",
  "input": {"city": "Beijing"}
}

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Streaming Event Types

Streaming responses use SSE format and include the following event types:

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message_start

Sent at the beginning of the stream, contains the Message object (with empty content): 
event: message_start
data: {"type":"message_start","message":{"id":"msg_abc123","type":"message","role":"assistant","content":[],"model":"claude-sonnet-4-20250514","stop_reason":null,"stop_sequence":null,"usage":{"input_tokens":15,"output_tokens":0}}}

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content_block_start

New content block begins: 
event: content_block_start
data: {"type":"content_block_start","index":0,"content_block":{"type":"text","text":""}}

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content_block_delta

Content block incremental update: 
event: content_block_delta
data: {"type":"content_block_delta","index":0,"delta":{"type":"text_delta","text":"Hello"}}

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content_block_stop

Content block ends: 
event: content_block_stop
data: {"type":"content_block_stop","index":0}

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message_delta

Message-level update (contains stop_reason and output token count): 
event: message_delta
data: {"type":"message_delta","delta":{"stop_reason":"end_turn","stop_sequence":null},"usage":{"output_tokens":20}}

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message_stop

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

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Complete Streaming Event Sequence

event: message_start
data: {"type":"message_start","message":{...}}

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_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","stop_sequence":null},"usage":{"output_tokens":5}}

event: message_stop
data: {"type":"message_stop"}
Crazyrouter fully supports Anthropic’s native streaming event format. You can also use Claude models through the OpenAI-compatible format (/v1/chat/completions), in which case the streaming format follows the standard OpenAI SSE format.