Cartesia API version 2026-08-14 and Sume TTS Router model ids

Cartesia released API version 2026-08-14, which cleans up multilingual voice support and drops fields that were already deprecated; the changelog says existing integrations keep running unchanged on their pinned version. On Sume the pin is a model: the TTS Router requires an explicit model from a fixed enum, with sonic-3.6 among the values.

Sources: the Cartesia 2026 changelog and Sume's API reference, read 2026-10-01.

What does a pinned version protect?

Cartesia says integrations on an older version are unchanged. The same page shows the other side of version pinning: for requests with Cartesia-Version: 2026-03-01 structured JSON errors are returned, while earlier versions keep the legacy error format. So behavior moves with the version header, and you opt in.

What is Sume's equivalent?

The Sume TTS Router request requires model, described as a required catalog model id passed through to the engine and not accepted on TTS 1.0. The enum in the schema is the list below, and the live catalog is GET /v1/tts-router/models.

Should I send an alias or a fixed id?

The Cartesia changelog advises pinning a dated snapshot, for example sonic-3.6-2026-08-27, for production traffic, and says a -latest alias can change without notice. The Sume enum has sonic-latest and sonic-preview, so apply the same caution: send an explicit id like sonic-3.6 when output stability matters. Whether Sume maps an alias to a particular snapshot is not stated in the cited schema.

What else should I check when I change models?

Text length (transcript up to 20000 characters) and speed (a [0.6, 1.5] multiplier in generation_config) are Sume-side limits that do not change with the model id. Dated retirements are covered in Sonic 2 and Turbo ending October 20.