Events

Iterating a RealtimeSession yields the session’s event stream: content parts, tool activity, turn boundaries, reconnects, and recoverable errors. The high-level stream_audio() and stream_transcripts() views described in Audio, images, and transcripts are derived from this same stream, so most applications iterate the session for control flow and leave media to the views.

If nothing is iterating the session, the session keeps the most recent 512 part delta events (audio, transcript, and text) and the most recent 512 structural events for a late async for; older ones are discarded. Discarding a part’s start discards the rest of that part with it, so a late iterator never receives a delta it cannot attach to a part. A failure parked for the consumer is never discarded.

Event reference

Event	Meaning
PartStartEvent	A speech, text, or tool part started.
PartDeltaEvent	Incremental speech audio/transcript or text content.
PartEndEvent	A finalized part; retained speech audio appears here, not at part start.
FunctionToolCallEvent	A local function tool began executing.
FunctionToolResultEvent	A local function tool completed or returned a retry prompt.
DeferredToolRequestsEvent	An inline capability handler resolved deferred requests.
DeferredToolResultsEvent	Inline deferred results are ready for normal tool processing.
EnqueuedMessagesEvent	Enqueued content was delivered into session history.
RealtimeInputSpeechStartEvent	The provider detected that the user started speaking, when the profile declares emits_input_speech_events.
RealtimeInputSpeechEndEvent	The provider detected the end of user speech, when the profile declares emits_input_speech_events.
RealtimeResponseInterruptedEvent	The provider reported an interrupted model response.
RealtimeInputTranscriptionErrorEvent	One user turn could not be transcribed; the session remains usable.
RealtimeOutputSpeechStartEvent / RealtimeOutputSpeechEndEvent	The model became, or stopped being, audible. These are emitted on a WebRTC sideband, where the provider owns audio playback.
RealtimeTurnCompleteEvent	The model finished replying and no tool remains active.
RealtimeSessionReconnectEvent	The connection was automatically re-established.
RealtimeSessionErrorEvent	A recoverable provider error occurred; the session remains usable.

Shared and realtime-only events

The first eight rows are AgentStreamEvent members from pydantic_ai.messages — the same events a standard streamed run yields, so event-handling code written for a text agent (rendering parts, logging tool calls) works on a session unchanged. The Realtime* rows are RealtimeEvent members that only a session emits: speech detection, interruption, turn completion, reconnection, and recoverable errors have no equivalent in a request-response run.

A capability’s event stream hooks see both kinds flow through the same stream; see Capabilities and hooks.

The turn boundary

Use RealtimeTurnCompleteEvent as the exchange boundary. A model can speak, call a tool, and speak again, so receiving speech — or a tool result — does not imply that the turn is done.

Reading raw audio events

The audio stream is these events under the hood: stream_audio() is a bounded view over the speech part deltas, and most applications should use it. As an advanced alternative, play SpeechPartDelta.audio_chunk from raw PartDeltaEvents. Model audio arrives in full whether or not history retention is enabled. When output audio is retained, the final SpeechPart contains the whole turn again as a WAV snapshot for history; do not play both or the turn will play twice.