> 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.

# Lightning v3.1 - choose day-first or month-first date reading

> The new optional date_format parameter controls whether all-numeric dates like 12/02/2025 are read day first or month first.

You can now choose how **all-numeric dates** such as `12/02/2025` are read out. Set the new optional **`date_format`** parameter on Lightning v3.1 requests:

| `date_format` | Order                                | `12/02/2025` reads as |
| ------------- | ------------------------------------ | --------------------- |
| `EU`          | Day first (`DD/MM`)                  | 12 February 2025      |
| `US`          | Month first (`MM/DD`)                | December 2, 2025      |
| omitted       | Unchanged. English reads month first | December 2, 2025      |

`date_format` is accepted on the dedicated `/waves/v1/lightning-v3.1/*` endpoints and on the unified `/waves/v1/tts` route, over HTTP, SSE streaming, and WebSocket. Any other value returns `400` with `invalid_enum_value` (options `EU`, `US`). Over WebSocket, the error arrives as a message with `status: "error"`.

Dates with the month written as a word, like `12 February 2025`, read the same with any setting.

**What changed in the docs:**

* [TTS Best Practices](/models/text-to-speech/best-practices) now shows default and `EU` readings for numeric dates.
* The Lightning v3.1 model card no longer recommends `DD/MM/YYYY` without `date_format`.