Streaming Output from Claude Agent SDK Agents

## Overview

By default the Agent SDK yields complete `AssistantMessage` objects after each
response. To receive incremental updates as text and tool calls are generated,
enable partial message streaming. This powers chat UIs and progress indicators.

## Enable streaming

Set `includePartialMessages` (TS) / `include_partial_messages` (Python) to `true`.
The SDK then also yields `StreamEvent` messages (TypeScript:
`SDKPartialAssistantMessage` with `type: "stream_event"`) carrying raw API events.

```typescript
for await (const message of query({
  prompt: "List the files in my project",
  options: { includePartialMessages: true, allowedTools: ["Bash", "Read"] },
})) {
  if (message.type === "stream_event") {
    const event = message.event;
    if (event.type === "content_block_delta" && event.delta.type === "text_delta") {
      process.stdout.write(event.delta.text);
    }
  }
}
```

## Read the deltas

- Text: `content_block_delta` events where `delta.type` is `text_delta` carry text
  chunks.
- Tool calls: `content_block_start` (tool begins), `content_block_delta` with
  `input_json_delta` (accumulate `partial_json`), and `content_block_stop` (call
  complete). Parse the accumulated JSON once complete.

## Message flow

With partial messages on, you receive `message_start`, `content_block_start`,
`content_block_delta` chunks, `content_block_stop`, `message_delta`,
`message_stop`, then the complete `AssistantMessage`, and finally a
`ResultMessage`. Without it, you receive the complete messages but no
`StreamEvent`s.

## Build a streaming UI

Track an `inTool` flag from `content_block_start`/`content_block_stop` to show a
status like `[Using Read...]` while a tool runs, and stream text only when not in
a tool. Print a completion marker on `ResultMessage`.

## Known limitation

Structured output does not stream as deltas; the JSON appears only in the final
`ResultMessage.structured_output`.

## Source

- Stream responses in real-time: https://code.claude.com/docs/en/agent-sdk/streaming-output