Streaming Delta Semantics - Aion Docs

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

Core Fields

Field	Meaning
`append`	`true` appends chunk content, `false` replaces content.
`lastChunk`	Reserved field, currently `false` during streaming.
`artifact.metadata.status`	`active` while streaming, `finalized` when complete.
`artifact.metadata.status_reason`	`chunk_streaming`, `complete_message`, or interrupt reason.

Typical Sequence

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

Example Chunk

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

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.