docs(realtime): describe the lazy Gemini Live setup built from the first session.update

[mateo-berri]

TLDR

• Gemini and Vertex Live setup is now built from the client's first session.update, so output_modalities and modalities apply
• Documents the connect-time session.created, the session.updated acknowledgement, and the text-to-audio downgrade on audio-only models
• Adds the LITELLM_GEMINI_LIVE_DEFER_SETUP row to the config settings table

Pairs with BerriAI/litellm#39864 (LIT-6974)

Merge after BerriAI/litellm#39864 lands, since these pages describe behavior that only exists once that PR ships

Type

📖 Documentation

---

Note

Low Risk
Documentation-only changes with no runtime impact; behavior described depends on the linked implementation PR landing first.

Overview
Updates Gemini and Vertex realtime provider docs and the LITELLM_GEMINI_LIVE_DEFER_SETUP env reference to match lazy Live setup behavior (companion implementation PR).

session.update is no longer described as ignored or connect-time-only: every update before the first content frame (conversation item, audio, or tool result) is merged into the single Gemini/Vertex setup, with session.updated acknowledgement; updates after content are ignored because setup is one-shot per connection. Default path sends setup with the first content frame, using merged session.update fields or model defaults when none were sent.

gemini_live_defer_setup is reframed as optional (default false): enable it only when clients stream audio or text before their session.update, so LiteLLM buffers that early traffic until the update can still shape setup. Vertex docs also note output_modalities: ["text"] on audio-only models is downgraded to audio with a proxy warning.

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Project	Deployment	Actions	Updated
litellm	Ready	Preview	Sep 5, 2026 6:00am UTC

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