When streaming_enabled is true on session creation, agent responses arrive incrementally as EVENT_TYPE_POLY_AGENT_MESSAGE_CHUNK events instead of a single EVENT_TYPE_POLY_AGENT_MESSAGE. This lets you display the response as it’s generated.
{
"type": "EVENT_TYPE_POLY_AGENT_MESSAGE_CHUNK",
"payload": {
"message_id": "msg_abc123",
"text": "I'd be happy to ",
"attachments": [],
"response_suggestions": [],
"chunk_index": 1,
"is_complete": false
}
}
| Field | Type | Description |
|---|
message_id | string | Same across all chunks of one message — use this to group them |
text | string | A fragment of text to append to the message |
attachments | array | Attachment(s) to append to the attachment list |
response_suggestions | array | Suggestion(s) to append to the suggestions list |
chunk_index | integer | 1-based index. Process chunks in this order. |
is_complete | boolean | true on the final chunk — the message is now complete |
Reassembling chunks
To reconstruct the full message, concatenate text and append attachments / response_suggestions from each chunk in order:
| Chunk | Received | Accumulated message |
|---|
| 1 | text: "Hello ", attachments: [A1], suggestions: [S1] | text: "Hello ", attachments: [A1], suggestions: [S1] |
| 2 | text: "there, ", attachments: [], suggestions: [] | text: "Hello there, ", attachments: [A1], suggestions: [S1] |
| 3 | text: "how can I help?", is_complete: true | text: "Hello there, how can I help?", attachments: [A1], suggestions: [S1] |
The final chunk (is_complete: true) may have empty text. It signals that the message is complete and may carry attachments or response suggestions that were only available after the full response was generated.
Example: handling chunks in JavaScript
const streamingMessages = {};
function handleChunk(payload) {
const { message_id, text, attachments, response_suggestions, chunk_index, is_complete } = payload;
if (!streamingMessages[message_id]) {
streamingMessages[message_id] = { text: "", attachments: [], suggestions: [] };
}
const msg = streamingMessages[message_id];
msg.text += text;
msg.attachments.push(...attachments);
msg.suggestions.push(...response_suggestions);
updateMessageInUI(message_id, msg);
if (is_complete) {
finalizeMessageInUI(message_id, msg);
delete streamingMessages[message_id];
}
}
Streaming flow
