> ## Documentation Index
> Fetch the complete documentation index at: https://docs.ag-ui.com/llms.txt
> Use this file to discover all available pages before exploring further.

# Event Streams

> The eight event families, and who reacts to each — draft

<Warning>
  **Draft — not yet ratified.** This document is published for review. It
  describes the intended 1.0 behaviour, its wording is not final, and nothing
  here is covered by a compatibility promise until a version is frozen. Do not
  cite it as a stable reference.
</Warning>

Everything a producer has to say arrives as events, in eight families. Each
family binds one of the [event patterns](/spec/draft/basic/patterns) and adds
its own rules; each is addressed to a different part of the consumer:

| Family                                            | Events                                                                          | Pattern        | Consumed by             |
| ------------------------------------------------- | ------------------------------------------------------------------------------- | -------------- | ----------------------- |
| [Runs and steps](/spec/draft/events/lifecycle)    | `RUN_STARTED` · `RUN_FINISHED` · `RUN_ERROR` · `STEP_STARTED` · `STEP_FINISHED` | lifecycle      | the client itself       |
| [Text messages](/spec/draft/events/text-messages) | `TEXT_MESSAGE_*`                                                                | streaming      | the UI                  |
| [Tool calls](/spec/draft/events/tool-calls)       | `TOOL_CALL_*`                                                                   | streaming      | the application         |
| [Reasoning](/spec/draft/events/reasoning)         | `REASONING_*`                                                                   | streaming      | the UI                  |
| [State](/spec/draft/events/state)                 | `STATE_SNAPSHOT` · `STATE_DELTA` · `MESSAGES_SNAPSHOT`                          | snapshot–delta | the application store   |
| [Activity](/spec/draft/events/activity)           | `ACTIVITY_SNAPSHOT` · `ACTIVITY_DELTA`                                          | snapshot–delta | the UI                  |
| [Subagents](/spec/draft/events/subagents)         | `SUBAGENT_STARTED` · `SUBAGENT_FINISHED` · `SUBAGENT_ERROR`                     | lifecycle      | the client itself       |
| [Passthrough](/spec/draft/events/passthrough)     | `RAW` · `CUSTOM`                                                                | standalone     | the application, opt-in |

The thirty-one event types these families comprise are enumerated on
[The Event Model](/spec/draft/basic), and their shapes are the
[schema](/spec/draft/schema)'s. Only the run lifecycle is mandatory for a
producer — every other family is a feature it emits when it has something to
say with it. A consumer MUST accept all of them: an event from a family a
consumer has no use for is still a well-formed event, not
[unrecognised material](/spec/draft/basic/processing).

<CardGroup cols={2}>
  <Card title="Runs and steps" href="/spec/draft/events/lifecycle">
    When a run begins and ends, and how steps mark its phases.
  </Card>

  <Card title="Text messages" href="/spec/draft/events/text-messages">
    The conversation itself, streamed as it is generated.
  </Card>

  <Card title="Tool calls" href="/spec/draft/events/tool-calls">
    The agent proposes, the application disposes.
  </Card>

  <Card title="Reasoning" href="/spec/draft/events/reasoning">
    The model's thinking, streamed, and the encrypted artefacts that
    round-trip it.
  </Card>

  <Card title="State" href="/spec/draft/events/state">
    Shared state and the conversation, replaced and amended.
  </Card>

  <Card title="Activity" href="/spec/draft/events/activity">
    Structured progress a UI renders outside the transcript.
  </Card>

  <Card title="Subagents" href="/spec/draft/events/subagents">
    Attribution, ownership, nesting, and how delegated work terminates.
  </Card>

  <Card title="Raw and custom events" href="/spec/draft/events/passthrough">
    The escape hatches, and their limits.
  </Card>
</CardGroup>