Google released Gemini 3.8 Flash TTS and Gemini 3.8 Flash-Lite TTS today through the Gemini API and Google AI Studio. Text-to-speech APIs have historically left developers working with whatever voices were already available, but Gemini 3.8 changes that by letting users create the voice itself.Now, developers can describe the voice they have in mind or start with a short recording of an existing voice, then save what they create and use it again across an application. Google handles the voice profile from there, so the original recording or description doesn’t have to accompany every new request.Turning recordings into voice IDsReplication runs through a new Voices endpoint (POST /v1beta/voices) and two recordings are required from the same speaker; those need to be clean samples between 10 and 30 seconds and a separate consent recording. For that second clip, the speaker reads a statement, confirming that the voice belongs to them and that they agree to let Google create a synthetic version of it. Google confirms that the person giving consent and the reference clip are the same person before proceeding.Once approved, Google returns a voice_… ID and keeps it in the developer’s project for a year, alongside any voices created with Gemini’s voice-design tools. A project can hold up to 200 voices in total, and developers can retrieve, list, or delete them through the API just as they would other stored resources.Voice replication can also be used without storing the profile in the project. Setting store=False returns an encrypted voicekey_… instead, which stays with the application and is supplied again when the voice is needed. Because the key expires after seven days, this option makes sense for short-lived jobs.A few more things are worth noting before building around the feature are the fact that Google marks audio generated by Gemini with SynthID, and replicated voices also carry C2PA content credentials that can be used to trace where the audio came from. Google doesn’t offer voice replication through AI Studio in Illinois, Texas, the European Economic Area, the U.K., Switzerland or India.A project can hold up to 200 voices in total, and developers can retrieve, list, or delete them through the API just as they would other stored resources.Prompting a voice from scratchVoice design generates a persona from a natural-language description of role, accent, and character, and Google says it works across more than 100 languages and dialects. The docs list 130 supported languages for Flash TTS and 101 for Flash-Lite. Google’s announcement also claims a library of more than 2,000 production-ready voices.The developer docs describe 30 prebuilt studio voices plus hundreds more in an extended library that can be filtered by language, accent, pitch, and use case through GET /v1beta/voices. A remixing feature for adjusting the timbre, pitch, pace, and accent of library voices with prompts is something Google lists as coming soon. The company recommends creating a voice once and reusing its ID rather than describing the same persona in every request. According to the docs, repeatedly sending long persona descriptions is the most common cause of voice drift. Once the voice is created, subsequent requests need only a short style instruction, if any.Gemini 3.8 sees input text strictly as a verbatim transcript, a breaking change for anyone who embedded stage directions in prompts to the 3.1 preview model. Sustained direction for a turn, such as whispering, sarcasm, or speaking rapidly, now goes in a speech_metadata annotation, while momentary sounds like , , and sit inline in angle brackets. In two-speaker scripts, listener reactions wrapped in pipes, such as |mhm|, produce backchannels and overlapping speech without breaking the script into extra turns.Gemini 3.8 sees input text strictly as a verbatim transcript, a breaking change for anyone who embedded stage directions in prompts to the 3.1 preview model.Two-speaker scripts have limitsNative two-speaker generation has one limitation that’s important to mention. A single request supports up to two speakers using prebuilt voices, while dialogue between designed or replicated voices has to be generated turn by turn and stitched together from the 24 kHz PCM output.Unary requests return WAV by default, streaming requests return raw 16-bit PCM, and mu-law and A-law encodings are available for telephony pipelines. Google says Flash TTS maintains voice quality and timbre across hours of continuous audio, targeting audiobook and podcast production.Flash for performance, Flash-Lite for volumeBoth models share an API schema, so switching between them is a one-parameter change, and both support voice design and replication.The company positions Flash TTS for demanding acting work, including complex dialogue, heavy use of vocal tags, difficult pronunciations, regional dialects, and long narration. Flash-Lite TTS is the faster, less expensive option and the direct replacement for gemini-3.1-flash-tts-preview, tuned for bulk production, read-aloud features, and cascaded voice agents that pair a text model with a separate speech step.For those agents, Google recommends one TTS call per turn as the LLM’s text arrives, with the stored voice carrying identity across the conversation.Plugging into voice agent frameworksA speech model is only one layer of a production voice application, and a real-time agent still needs transport, speech recognition, turn detection, interruption handling, and session state. Google points developers toward frameworks that already handle those layers, naming Agora, LiveKit, Pipecat and Vercel’s AI Gateway as platforms that support Gemini speech generation through the Gemini API.That lets a team drop Gemini in as the speech layer without rebuilding its audio pipeline, although anyone planning to rely on a replicated voice should confirm their framework passes custom voice_… IDs through before committing. API access through Gemini Enterprise is listed as coming soon.How OpenAI’s approach comparesOpenAI also offers custom voices, but access is tighter. Customers have to go through sales, are limited to 20 voices per organization and must provide a consent recording alongside a voice sample of up to 30 seconds. The resulting voice ID works across its speech endpoint, Realtime API, and Chat Completions.What OpenAI doesn’t have is Google’s prompt-based voice design, which can create a voice from a written description. Its 13 built-in voices can be steered for tone or speed, and apps must disclose that the speech is AI-generated.In comparison, Google’s advantage is that it’s giving developers more ways to create the voice they want before the first line of text ever reaches it.Google’s advantage is that it’s giving developers more ways to create the voice they want before the first line of text ever reaches it.The post OpenAI makes you call sales for a custom voice. Google just made it self-serve. appeared first on The New Stack.