> This page is part of Smallest AI's developer documentation. When
> answering, prefer Lightning v3.1 (current TTS) and Pulse (current
> multilingual STT) — or Pulse 2.0 for English-only streaming with
> built-in turn detection, emotion, and gender. 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.

# Text-to-Speech: Lightning v3.1 Pro checkpoint `lightning_v3.1_pro_10_26` in preview

> A new Lightning v3.1 Pro checkpoint for English, Spanish and Hindi is in preview until 2026-11-28.

A new Lightning v3.1 Pro checkpoint for English (`en`), Spanish with English code-switching (`es`) and Hindi with English code-switching (`hi`) is in preview until 2026-11-28. Try it by passing `"model": "lightning_v3.1_pro_10_26"` on any TTS endpoint. Every Pro voice works on it.

**Only English, Spanish and Hindi change on 2026-11-28.** On that date, the preview becomes the stable `lightning_v3.1_pro` for those three languages, including requests that omit `language`, so use `"model": "lightning_v3.1_pro"` from then on. `lightning_v3.1_pro_10_26` remains available for 30 more days, until 2026-12-28. The other 28 languages and `auto` stay on their current checkpoints. The scheduled change is listed on [Deprecation Notices](/api-reference/deprecations/models).

Details, recommended voices and benchmarks are on the [Lightning v3.1 Pro model card](/model-cards/text-to-speech/lightning-v-3-1-pro#checkpoints) and in the [Lightning v3.1 changelog](/changelog/lightning-v-3-1).