Same card, new defaults
Google priced Gemini 3.8 Live with the preview it replaces, and moved four defaults under the model string
Two voice models went generally available on 15 September on one rate card with gemini-3.1-flash-live-preview. Swap the string and asynchronous tool calls, always-on proactive audio and video on every turn come with it.
| Setting | gemini-3.8-live | gemini-3.8-live-extended-thinking |
|---|---|---|
| Function calls | NON_BLOCKING by default; BLOCKING per tool | NON_BLOCKING only; BLOCKING is a hard error |
| thinking_level | not accepted | low, medium or high; MINIMAL refused |
| proactive_audio: false | returns an error | returns an error |
| Affective dialogue | removed from the API | removed from the API |
| turnComplete: true | interrupts generation | no longer means idle; read interaction_status |
| Video frames | sent by default | sent by default |
Google released gemini-3.8-live on 15 September with asynchronous tool calls as the default and the preview’s price.
Its sibling, gemini-3.8-live-extended-thinking, went generally available the same day, and the pricing page lists both with gemini-3.1-flash-live-preview, the model the migration notes tell you to leave. The price is not the story. The defaults are: a model string swap that costs nothing changes what your tool calls do, what the model says unprompted, and what a finished turn means.
The card reads $0.75 per million text tokens in and $4.50 out, with thinking tokens billed as output. Audio in is $3.00 per million tokens, which Google also states as $0.005 a minute. Audio out is $12.00 per million, or $0.018 a minute. OpenAI’s nearest figure, gpt-live-1 at $0.05 a minute of session with the backend model charged separately, is a different unit, and the comparison stops there.
The default that moves first is tool execution. On gemini-3.8-live, the migration notes say, behavior: NON_BLOCKING “is now the default function calling mode”, so a tool call no longer pauses the conversation until your code answers; the model keeps talking and takes the result when it arrives. Code that relied on the pause gets it back only by declaring behavior: BLOCKING on each tool. On the Extended Thinking model there is no way back: synchronous mode “is not supported and returns a hard error”.
The second is what a finished turn means. On Extended Thinking, “turnComplete: true no longer indicates that the model is idle”; the server may still be reasoning or waiting on a tool, and the client must keep listening and read an interaction_status field that moves between IN_PROGRESS and IDLE. A client that stops listening on turnComplete misses what follows.
Three settings stop being settings. proactive_audio is “permanently enabled” and passing false “returns an error”; enable_affective_dialog “is removed from the API”; and thinking_level “is not supported for gemini-3.8-live”, so the dial the preview exposed is gone on the cheap model and present only on the expensive one, where MINIMAL is refused. Video frames now reach the model on every turn under TURN_INCLUDES_AUDIO_ACTIVITY_AND_ALL_VIDEO, which Google’s note says to send only when needed “to manage context and cost”.
The independent measurement says the dial mattered. On Artificial Analysis’s agentic column, read today, the preview at its high setting scores 37.7 against 30.1 for the new default model, and Extended Thinking scores 68.6, above both. The new default answers faster, 1.18 seconds to first audio against the preview’s 2.99, and scores higher on conversational dynamics.
Google’s post, by Tom Ouyang and Malini Jaganathan of the Gemini audio team, claims first place on that index, ahead of every other listed model, and the index agrees. It also claims 68.6 per cent on τ-Voice, the same as the figure in Artificial Analysis’s agentic column, and neither page says whether that column is an independent run or Google’s number reproduced.
The obvious objection is that nothing is retired: the deprecations page gives gemini-3.1-flash-live-preview no shutdown date, so nobody has to move today. It holds for today. Google’s changelog calls Gemini 3.8 Live “the default option”, and a preview left on the card without a date is where the migration notes expect you to leave from.
The paper’s verdict: on the preview with tool calls that assume a pause, do not swap the string this week; add behavior: BLOCKING to every tool declaration first, then swap. On the preview at thinking level high for agentic work, the replacement is not gemini-3.8-live but Extended Thinking, at the same price and with no blocking tools at all.
Neither model supports caching, so a long voice session pays full price for every token of its own history until it reaches the input cap.
What it changes On the preview with tools that assume a pause: declare behavior: BLOCKING on each tool before you change the model string. On the preview at thinking level high: move to Extended Thinking, not 3.8 Live, and rewrite the client to poll interaction_status rather than stop on turnComplete.
Primary source read
Gemini API release notes, 15 September entry Gemini API pricing Gemini 3.8 Live model page, migration notes Gemini 3.8 Live Extended Thinking model page Gemini API deprecations Introducing Gemini 3.8 Live and 3.8 Live Extended Thinking Speech to Speech Index, model table OpenAI API pricing, GPT-Live sessions