Cartesia Line SDK hosting ends Dec 1 2026: does batch TTS change?

If you host voice agents on Cartesia's Line SDK, plan to move them: Cartesia's 2026 changelog says hosting for Line SDK agents ends on December 1, 2026, and that LLM usage charges for agents started on October 1. That is an agent-hosting change. Nothing on the page I read says the Sonic text-to-speech models change because of it, and Sume's TTS Router calls Sonic as a model by id, not as an agent host.

I treat the second half of that sentence as a reading of two separate products, not a promise. Confirm with Cartesia before you rely on it.

Dates that matter

Dates are from Cartesia's changelog and older-models page. The Sume column is from the TTS Router docs.

• The Cartesia changelog also mentions Ink-2 multilingual in September, which is not part of Sume's TTS catalog.

Check your own exposure in four steps

• List every place you call Cartesia: agent hosting, Sonic over API, or Sume's TTS Router.
• For agent hosting, plan a move before December 1.
• For model ids, replace anything on the October 20 list with sonic-3.6.
• Call GET /v1/tts-router/models and keep only the ids it returns.

import os, requests

r = requests.post(
    "https://api.sume.com/v1/tts-router/generate",
    headers={
        "Authorization": f"Bearer {os.environ['SUME_API_KEY']}",
        "Idempotency-Key": "tts-demo-001",
    },
    json={
        "model": "sonic-3.6",
        "transcript": "Welcome back. Today we compare three prices.",
        "voice": {"id": os.environ["SUME_VOICE_ID"]},
        "timestamps": {"words": True},
    },
    timeout=30,
)
r.raise_for_status()
print(r.json())

Why the line between products matters

A voice agent is a service: it listens, thinks, and speaks, and the host runs all three. A batch TTS job is one function: text in, audio out. Changes to the first do not follow automatically into the second, but pricing and quality of the shared voices can move in step. Track both pages, and keep a log of the voice and model id that produced each file.

A short migration plan

Treat the next eight weeks as a checklist. This week, inventory every Cartesia dependency. By October 20, move any Sonic model id that is on the sunset list. By mid-November, have agent hosting running somewhere new, with a rollback path. By December 1, confirm nothing still points at the old host.

For batch work the plan is shorter: pin sonic-3.6 in your Sume requests, re-render one approved script, and store the result as your reference take. If a later change alters the voice, you will notice within a run rather than after a release.

What Sume does not do

Sume does not host voice agents on Cartesia's SDK and does not run live calls. Sume TTS covers Cartesia Sonic only. The router has no Eleven, OpenAI, Gemini, MAI or Inworld engines, no streaming TTS, and no routing presets. Jobs are asynchronous, and any audio over 1,200 seconds fails with tts_duration_exceeded. I did not verify whether Cartesia self-hosting options changed in September; sources I saw disagreed, so I make no claim on it.

Related

For the model sunset dates see Sonic 2 and Turbo stop on October 20 and the alias guide for old model strings.