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Streaming responses are emitted as artifact-update events. The main artifact used for delta streaming is typically stream_delta.

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Core Fields

FieldMeaning
appendtrue appends chunk content, false replaces content.
lastChunkReserved field, currently false during streaming.
artifact.metadata.statusactive while streaming, finalized when complete.
artifact.metadata.status_reasonchunk_streaming, complete_message, or interrupt reason.

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Typical Sequence

  1. First chunk with append: false.
  2. Intermediate chunks with append: true.
  3. Finalized event, often with complete assembled parts.

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Example Chunk

{
  "kind": "artifact-update",
  "append": true,
  "artifact": {
    "artifactId": "stream_delta",
    "metadata": {
      "status": "active",
      "status_reason": "chunk_streaming"
    },
    "parts": [
      {
        "kind": "text",
        "text": " World!"
      }
    ]
  }
}

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Reconstruction Rule

A finalized artifact may later be reconstructed within the same task after an interruption or resume flow. Clients should treat the latest finalized artifact as source of truth.