OptionalAudioAudio encoding and sample rate format supported or negotiated for this session.
Capability introspection. A small, static description of what THIS live session can do, so the
container can ask "is it safe to call X?" instead of invoking optional methods that silently no-op (or
can't be supported) on some providers — the same role IBridgeProviderFeatures plays for bridges and
BaseRealtimeModel.SupportsClientDirect plays for minting. Optional: a driver that hasn't
declared its capabilities is treated conservatively (everything unsupported). As models gain
abilities, drivers just flip a flag — no container changes.
The PCM sample rate (Hz) this model consumes on IRealtimeSession.SendInput — its audio INPUT format. Optional; consumers default to 24000 (OpenAI Realtime). Gemini Live = 16000. A server-bridged host (LiveKit/Zoom/Teams) MUST resample inbound room audio to this rate or the model receives mis-rated audio it can't parse (the symptom: the agent never responds on the bridge while the same model works client-direct, where the browser negotiates the rate itself).
The PCM sample rate (Hz) this model emits on IRealtimeSession.OnOutput — its audio OUTPUT format. Optional; consumers default to 24000 (both OpenAI and Gemini Live emit 24 kHz today).
Current task revision counter for cancellation and supersede-and-discard.
Advances the task revision counter, causing in-flight tool results from prior revisions to be discarded.
Closes the session and releases the underlying provider connection.
A promise that resolves once the session is fully closed.
Optional capability — registers a handler invoked when the underlying provider
connection closes WITHOUT the consumer having called IRealtimeSession.Close
(provider-side hangup, network drop). Not fired for a consumer-initiated Close() —
the caller already knows about that one.
Optional because not every provider surface exposes a close signal cheaply; callers
must feature-detect (if (session.OnClose) { ... }). An unexpected close is typically
ALSO surfaced as a Fatal IRealtimeSession.OnError, which is the signal
consumers should drive finalization from.
Invoked when the provider connection closes unexpectedly.
Registers a handler for session errors.
Fatality semantics mirror the client-side BaseRealtimeClient contract:
Fatal: true — the session is unusable (transport/socket failure, credential/token
expiry, unexpected connection loss). The consumer should finalize the session (e.g.
RealtimeSessionRunner calls Stop()) instead of idling forever on a dead socket.Fatal: false — a provider-reported, recoverable error frame; the session stays open
and the consumer should log and continue.Invoked with each RealtimeSessionError.
Registers a handler for provider-detected interruptions (barge-in).
True barge-in only: the handler fires ONLY when user speech interrupts ACTIVE model output — NOT on every user utterance. A user simply taking their normal turn while the model is idle is not an interruption, and drivers must not report it as one (e.g. a raw "speech started" frame must be gated on whether a model response is actually in flight).
Turn detection / VAD is owned by the provider. The agent layer uses this hook to cancel
the model's current turn and to fire the cancellationToken of any in-flight
delegated agent run — a stale delegated result must never be narrated into a conversation
that has moved on.
Invoked when the provider reports a true barge-in interruption.
Registers a handler for model audio output frames (the audio media plane).
Invoked with each output audio frame as an ArrayBuffer.
Registers a handler for model tool-call requests.
Consumers execute the requested tool (under the session's context user) and feed the result back to the model.
Invoked with each RealtimeToolCall.
Registers a handler for transcript events (the text stream).
Consumers typically forward these to the control plane and persist them as
ConversationDetail records.
Invoked with each RealtimeTranscript (partial or final).
Registers a handler for usage/telemetry updates.
Usage is checkpointed incrementally by the agent layer (debounced onto the prompt run) so partial usage is never lost if the session is force-closed after a crash.
Invoked with each RealtimeUsage update.
Registers the set of tools the model may call, translating them into the provider's native function-calling format.
The Core-level RealtimeToolDefinition is intentionally minimal: BaseRealtimeModel
lives in the lowest AI layer and cannot depend on the richer tool metadata defined in
higher packages (the agent layer) — doing so would create an illegal upward/circular
dependency. The agent layer is responsible for mapping its richer tool metadata down
to this Core type before calling RegisterTools, and the concrete driver maps this Core
type up to the provider's native function-calling schema.
Note that some providers (e.g. Eleven Labs) bind to a pre-declared tool set on a server-side agent configuration; for those, the driver maps these definitions onto the pre-declared tool names rather than registering arbitrary schemas at session start.
Idempotency rule: a post-start registration of a set IDENTICAL to the set supplied at connect time (via RealtimeSessionParams.Tools) MUST be a no-op. Providers that bind their tool set at connect time and cannot re-declare schemas on an open session MUST no-op (and may log) rather than degrade the conversation — e.g. by injecting schema text into the conversation as content. A genuinely DIFFERENT post-start set on such a provider is unsupported and should be surfaced as a warning, not silently mangled.
The tools to expose to the model.
Optional capability — asks the model to voice one brief interim update following the given instructions (e.g. "In one short sentence, tell the user the report agent has finished gathering data and is now drafting"). Used by the agent layer to narrate delegated-run progress while a long-running tool/agent call is still in flight.
Implementations must not collide with an in-flight model response: providers reject or garble overlapping generation requests. A driver must either queue the request until the current response completes or skip it outright — skipping is explicitly acceptable because interim updates are disposable by contract (a stale "still working…" line has no value once the real result lands; the next update or the final result supersedes it).
Like IRealtimeSession.SendContextNote, this is optional because it models provider capability: drivers whose provider cannot trigger an instructed, one-off spoken response mid-session omit the member, and callers must feature-detect before invoking.
Instructions for the single spoken update (tone, brevity, content).
true when a response was actually triggered, false when it was skipped (e.g. a response
is already in flight). A bridge that claimed the speaking floor for this turn uses this to release the
floor immediately on a skip — otherwise a skipped trigger would wedge the room until the safety timer.
void/undefined from legacy drivers is treated as "triggered" for backward compatibility.
Optional capability — injects background context (e.g. delegated-run progress, freshly retrieved data, or a state change the model should be aware of) into the model's conversation without forcing a spoken reply. The model simply has the note available the next time it speaks.
This is the server-side counterpart of the client-direct BaseRealtimeClient.SendContextNote
capability: in the server-bridged topology, the agent layer (e.g. a session runner observing
a delegated agent run) calls this to keep the realtime model informed of long-running work
so it can narrate naturally when asked or when it next takes the floor.
Optionality models capability, not laziness: not every provider supports injecting
conversation items into an already-open session (some only accept media frames and tool
results mid-session). Drivers that cannot inject mid-session omit the member entirely, and
callers must feature-detect (if (session.SendContextNote) { ... }) rather than assume it.
The context note to append to the conversation (plain text; the caller owns any prefixing/framing policy such as "[progress]" markers).
Sends a client media frame to the model.
Fire-and-forget: frames are streamed straight to the provider with no JSON intermediation. The
optional kind tags the media plane — 'audio' (default, back-compatible: existing callers and
audio-only drivers need not pass or read it) or 'video' for a camera frame to a video-capable
model (one that BaseRealtimeModel.SupportsVideo). Audio-only drivers ignore 'video'
frames.
A raw media frame as an ArrayBuffer.
Optionalkind: "audio" | "video"The media plane the frame belongs to. Defaults to 'audio'.
Mid-session instruction update (e.g. OpenAI session.instructions.append).
New or appended instructions for the ongoing session.
Send the result of an executed tool/function call back to the model so it can continue the
turn. output is the JSON-stringified tool result. Called by the agent layer after it handles
an IRealtimeSession.OnToolCall.
The CallID from the originating RealtimeToolCall, used to correlate the result.
The tool's result as a JSON-stringified string.
OptionaltaskRevision: numberOptional task revision counter from the tool call. If supplied and mismatched, stale results are discarded.
A promise that resolves once the result has been sent to the provider.
Waits until the initial session.started confirmation frame arrives from the server.
Live IRealtimeSession handle speaking the OpenAI Live wire protocol (
wss://api.openai.com/v1/live/sessions).