ADK Events — The Agent's Event Stream

Why it matters

Event-based model makes agents debuggable and testable. Understanding events unlocks observability.

The architecture

Event types: user turn, model turn, tool call, tool response, control (session change).

Content: message parts, tool call args, tool results.

How it works end to end

Streaming: events emitted as they happen. UI subscribes and updates.

Persistence: events part of session; persisted with session state.

Callbacks: hook into event lifecycle for custom processing.

Filtering: emit certain events only or transform before sending.