Dedicated Messages Chunk Object

event: message_start
data: {
  "type": "message_start",
  "message": {
    "id": "msg_4b71d12c86d94e719c7e3984a7bb7941",
    "type": "message",
    "role": "assistant",
    "content": [],
    "stop_reason": null,
    "stop_sequence": null,
    "usage": { "input_tokens": 0, "output_tokens": 0, "cache_read_input_tokens": 0 }
  }
}

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": ", how can I help?" }
}

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": 11 }
}

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

event: message_start
data: {
  "type": "message_start",
  "message": {
    "id": "msg_4b71d12c86d94e719c7e3984a7bb7941",
    "type": "message",
    "role": "assistant",
    "content": [],
    "stop_reason": null,
    "stop_sequence": null,
    "usage": { "input_tokens": 0, "output_tokens": 0, "cache_read_input_tokens": 0 }
  }
}

event: content_block_start
data: {
  "type": "content_block_start",
  "index": 0,
  "content_block": { "type": "tool_use", "id": "toolu_01A", "name": "get_weather", "input": {} }
}

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "input_json_delta", "partial_json": "{\"location\":\"Seoul\"" }
}

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "input_json_delta", "partial_json": ",\"date\":\"2026-03-12\"}" }
}

event: content_block_stop
data: { "type": "content_block_stop", "index": 0 }

event: message_delta
data: {
  "type": "message_delta",
  "delta": { "stop_reason": "tool_use", "stop_sequence": null },
  "usage": { "output_tokens": 19 }
}

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

event: message_start
data: {
  "type": "message_start",
  "message": {
    "id": "msg_4b71d12c86d94e719c7e3984a7bb7941",
    "type": "message",
    "role": "assistant",
    "content": [],
    "stop_reason": null,
    "stop_sequence": null,
    "usage": { "input_tokens": 0, "output_tokens": 0, "cache_read_input_tokens": 0 }
  }
}

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

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "thinking_delta", "thinking": "I should answer briefly." }
}

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "signature_delta", "signature": "sig_abc123" }
}

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": 8 }
}

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

Represents a streamed chunk returned when streaming the messages API, based on the provided input.

event: message_start
data: {
  "type": "message_start",
  "message": {
    "id": "msg_4b71d12c86d94e719c7e3984a7bb7941",
    "type": "message",
    "role": "assistant",
    "content": [],
    "stop_reason": null,
    "stop_sequence": null,
    "usage": { "input_tokens": 0, "output_tokens": 0, "cache_read_input_tokens": 0 }
  }
}

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": ", how can I help?" }
}

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": 11 }
}

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

event: message_start
data: {
  "type": "message_start",
  "message": {
    "id": "msg_4b71d12c86d94e719c7e3984a7bb7941",
    "type": "message",
    "role": "assistant",
    "content": [],
    "stop_reason": null,
    "stop_sequence": null,
    "usage": { "input_tokens": 0, "output_tokens": 0, "cache_read_input_tokens": 0 }
  }
}

event: content_block_start
data: {
  "type": "content_block_start",
  "index": 0,
  "content_block": { "type": "tool_use", "id": "toolu_01A", "name": "get_weather", "input": {} }
}

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "input_json_delta", "partial_json": "{\"location\":\"Seoul\"" }
}

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "input_json_delta", "partial_json": ",\"date\":\"2026-03-12\"}" }
}

event: content_block_stop
data: { "type": "content_block_stop", "index": 0 }

event: message_delta
data: {
  "type": "message_delta",
  "delta": { "stop_reason": "tool_use", "stop_sequence": null },
  "usage": { "output_tokens": 19 }
}

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

event: message_start
data: {
  "type": "message_start",
  "message": {
    "id": "msg_4b71d12c86d94e719c7e3984a7bb7941",
    "type": "message",
    "role": "assistant",
    "content": [],
    "stop_reason": null,
    "stop_sequence": null,
    "usage": { "input_tokens": 0, "output_tokens": 0, "cache_read_input_tokens": 0 }
  }
}

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

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "thinking_delta", "thinking": "I should answer briefly." }
}

event: content_block_delta
data: {
  "type": "content_block_delta",
  "index": 0,
  "delta": { "type": "signature_delta", "signature": "sig_abc123" }
}

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": 8 }
}

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

Events

`event: message_start` chunk object

string

required

Always message_start.

object

required

Initial response envelope for this streamed message.

Show child attributes

string

required

Unique ID of the response message.

string

required

Object type, always message.

string

required

Author role of streamed output, always assistant.

object[]

required

Initialized as an empty array at start. Populated by subsequent block events.

enum<string> | null

Stop reason placeholder at start.Available options: end_turn, max_tokens, tool_use, stop_sequence

string | null

Matched stop sequence placeholder at start.

object

required

Running usage object.

Show child attributes

integer

required

Number of billed input tokens.

integer

required

Number of billed output tokens currently emitted.

integer | null

Number of cached input tokens read, when applicable.

string | null

Model identifier for this response, when available.

`event: content_block_start` chunk object

string

required

Always content_block_start.

integer

required

Index of the content block in the response content array.

object

required

Initial content block payload.

Show child attributes

enum<string>

required

Content block type.Available options: text, thinking, tool_use

string

Text content when type=text.

string

Reasoning content when type=thinking.

string | null

Optional signature when type=thinking.

string

Tool call ID when type=tool_use.

string

Tool name when type=tool_use.

object

Parsed tool input object when type=tool_use.

`event: content_block_delta` chunk object

string

required

Always content_block_delta.

integer

required

Index of the content block being updated.

object

required

Incremental delta payload.

Show child attributes

enum<string>

required

Delta type.Available options: text_delta, thinking_delta, signature_delta, input_json_delta

string

Text fragment when type=text_delta.

string

Reasoning fragment when type=thinking_delta.

string

Signature fragment when type=signature_delta.

string

Partial JSON fragment for tool arguments when type=input_json_delta.

`event: content_block_stop` chunk object

string

required

Always content_block_stop.

integer

required

Index of the block that has finished streaming.

`event: message_delta` chunk object

string

required

Always message_delta.

object

required

Final message-level delta.

Show child attributes

enum<string> | null

Why generation stopped.Available options: end_turn, max_tokens, tool_use, stop_sequence

string | null

Matched stop sequence when stop_reason=stop_sequence.

object | null

Usage delta object that may be emitted near stream completion.

Show child attributes

integer | null

Input token count delta when included.

integer | null

Output token count delta when included.

integer | null

Cached input token count delta when included.

`event: message_stop` chunk object

string

required

Always message_stop. Indicates stream completion.

`event: error` chunk object

string

required

Always error.

object

required

Error payload object.

Show child attributes

string

required

Error category, such as invalid_request_error.

string

required

Human-readable error message.

string | null

Request identifier for debugging and support.

Last modified on July 8, 2026

Dedicated Responses Chunk Object

Dedicated Completions Chunk Object

⌘I

API Reference

Model APIs

Dedicated

Container

Administration

Dataset and File

Friendli SDK

Dedicated Messages Chunk Object

Events

`event: message_start` chunk object

`event: content_block_start` chunk object

`event: content_block_delta` chunk object

`event: content_block_stop` chunk object

`event: message_delta` chunk object

`event: message_stop` chunk object

`event: error` chunk object

​Events

​event: message_start chunk object

​event: content_block_start chunk object

​event: content_block_delta chunk object

​event: content_block_stop chunk object

​event: message_delta chunk object

​event: message_stop chunk object

​event: error chunk object

Events

`event: message_start` chunk object

`event: content_block_start` chunk object

`event: content_block_delta` chunk object

`event: content_block_stop` chunk object

`event: message_delta` chunk object

`event: message_stop` chunk object

`event: error` chunk object