Delta format - Nito

Transport: Server-Sent Events.

The Chunk

Field	Type	Notes
`id`	string	Completion identifier. Stable across the stream.
`object`	string	Always `chat.completion.chunk`.
`created`	integer	Unix seconds.
`model`	string	The model serving the call.
`choices`	array	Streamed choices. Each carries `index`, `delta`, `finish_reason`.
`usage`	object	Optional. Present only on the trailing usage chunk. See Stream termination.
`web_search`	object	Optional. Present when a web search ran.
`error`	object	Optional. Present on a mid-stream error chunk. See Error events.
`free_tier`	object	Optional. Present on Free plan-eligible calls.

Choice and Delta

Field	Type	Notes
`choices[].index`	integer	Choice index (always `0`).
`choices[].delta`	object	The incremental update. See below.
`choices[].finish_reason`	string or null	`null` until the terminal chunk, then one of `stop`, `length`, `tool_calls`, `error`. See Finish reasons.

Delta Fields

Field	Type	Notes
`role`	string	Optional. `assistant`, sent once at the start.
`content`	string	Optional. A fragment of the reply to append.
`tool_calls`	array	Optional. Tool-call fragments. See Tool call streaming.
`reasoning_details`	array	Optional. Reasoning summary fragments. See Reasoning parameters.

Accumulating

The stream is incremental. role arrives once on the first delta. content arrives as fragments to concatenate in order. finish_reason is null until the terminal chunk.

{ "id": "...", "object": "chat.completion.chunk", "created": 1751299200, "model": "z-ai/glm-5.2",
  "choices": [ { "index": 0, "delta": { "role": "assistant", "content": "A gateway" }, "finish_reason": null } ] }

{ "id": "...", "object": "chat.completion.chunk", "created": 1751299200, "model": "z-ai/glm-5.2",
  "choices": [ { "index": 0, "delta": { "content": " is a single entry point." }, "finish_reason": null } ] }

{ "id": "...", "object": "chat.completion.chunk", "created": 1751299200, "model": "z-ai/glm-5.2",
  "choices": [ { "index": 0, "delta": {}, "finish_reason": "stop" } ] }

After the terminal chunk come the optional usage chunk and [DONE].