What you can build with streaming text-to-speech

Streaming changes what a text-to-speech API is good for. Once audio arrives as it’s generated instead of all at once, a whole class of real-time features becomes practical. The Speechify streaming endpoints give you two things to build on: a low-latency audio stream (POST /v1/audio/stream) and, when you want it, word-level timing alongside that audio (POST /v1/audio/stream/with-timestamps). What each unlocks:

What the audio stream gives you

The plain stream is about one thing: the first sound arrives fast, and the rest follows as it’s made. That’s the foundation for anything interactive.

• In-app read-aloud. A listen button that plays the moment it’s pressed. Playing straight into the browser is a well-worn path; the Web Audio API walkthrough covers it.
• Voice agents and assistants. Conversation needs the reply to start speaking quickly. Streaming the response as the model produces it keeps the exchange from stalling.
• Phone and call narration. No screen means no way to mask a delay, so streaming the audio into the call is what keeps the line from going quiet.

What speech marks add

Ask for timestamps and the stream also carries a speech mark per word, each with a start and end time in milliseconds. That timing is what lets you sync anything visual to the voice.

• Live captions and read-along highlighting. Words light up exactly as they’re spoken. The real-time captions build shows the pattern.
• Karaoke-style readers and language tools. The same timing drives follow-along interfaces where seeing and hearing the word together is the point.

The one number that ties it together

All of it comes back to time to first byte. Streaming exists to shrink the gap between “the user asked” and “the audio started,” and every feature above is really just a different surface for that. Use a streaming-native Simba 3 model (simba-3.2 for English, simba-3.0 for multilingual) to keep that gap small.

For the production-side framing rather than the build-side one, a companion piece, 7 use cases for streaming TTS in production apps, covers where these ship.

FAQ

What’s the difference between the two streaming endpoints? POST /v1/audio/stream streams audio only. POST /v1/audio/stream/with-timestamps streams the same audio plus word-level speech marks, so you can highlight or sync text without a second request.

Do I need speech marks for read-aloud? No. Plain streaming is enough to play audio as it arrives. You only need speech marks when you want to show which word is being spoken, like captions or read-along highlighting.

Which model works with the streaming endpoints? The streaming-native Simba 3 models, simba-3.0 and simba-3.2. They start emitting audio quickly, which is the whole point of streaming.

Is streaming harder to implement than batch? A little, because you consume a stream instead of a single response, but the demos linked above are small. The payoff is the latency users actually feel.