> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> STT). Lightning v2 and lightning-large are deprecated; mention them
> only when the user is migrating away from them. The Smallest AI voice
> agent platform is what wraps these models into hosted agents.

# Speech-to-Speech: Hydra V1.1 released, `?model=hydra` deprecated

> Hydra V1.1 is the current release of the realtime speech-to-speech model.

Hydra V1.1 is the current release of the realtime speech-to-speech model. New integrations should connect with `?model=hydra-v1.1`:

```
wss://api.smallest.ai/waves/v1/s2s?model=hydra-v1.1&api_key=<SMALLEST_API_KEY>
```

The session protocol (event catalog, `session.configure` shape, tool calling, interruption handling) is identical to the original `hydra`, so switching is a one-parameter change on the query string.

**`?model=hydra` is deprecated.** Existing sessions still open, but the server emits a `warning` frame with `code: "model_deprecated"` immediately before `session.created`. Migrate to `?model=hydra-v1.1`. See [Deprecation Notices](/api-reference/deprecations/models).

**Voice rosters** are documented per version on the [Hydra model card](/model-cards/speech-to-speech/hydra). An unknown voice on `session.configure` is rejected with an `error` frame (`code: "invalid_request_error"`) rather than silently defaulted, so validate client-side.

**`hydra-v1.0` is also served** on the same endpoint; it is not deprecated, and the server names it as the migration target when a client connects with the deprecated `?model=hydra`.

Full voice + version reference on the [Hydra model card](/model-cards/speech-to-speech/hydra). Overview + docs pages ([overview](/models/speech-to-speech/overview), [WebSocket connection](/models/speech-to-speech/web-socket-connection), [Audio I/O](/models/speech-to-speech/audio-i-o), [Managing sessions](/models/speech-to-speech/managing-sessions), [Tool calling](/models/speech-to-speech/tool-calling)) point at `?model=hydra-v1.1` in every URL example and use a V1.1 voice in the sample payloads. The `voice` field in **Managing sessions** points to the model card, which is the single source of truth for per-version voice tables, and documents the rejection of unknown voices.