> ## Documentation Index
> Fetch the complete documentation index at: https://docs.cartesia.ai/llms.txt
> Use this file to discover all available pages before exploring further.
# Changelog 2026
> Product, API, and platform changes for 2026
### Sonic 3.5
*Sonic 3.5 is now available on `sonic-3-latest`. We'd love for you to try it and tell us what you think.*
#### Why you should try it
* **More natural speech, pacing, and emotional expression**, especially noticeable on expressive, conversational, and support-style transcripts.
* **Cleaner audio quality** across all languages and voices.
* **Better alphanumeric read-out** — confirmation codes, order numbers, phone numbers, IDs, and emails sound meaningfully more natural, in all supported languages.
* **Step-change multilingual performance**, particularly Hebrew, Japanese, Spanish, Hindi, German, Korean, and French.
* **English heteronyms** — tricky English heteronyms like "read," "bass," and "bow" now pronounce correctly in context.
#### How to try it
1. Point your API call or Playground request to the model ID `sonic-3-latest`.
2. Keep your existing voice IDs, request shape, and prompting — no code changes required for most customers.
3. Send us feedback on any voice or transcript that behaves differently than you expect.
As with any `-latest` alias, `sonic-3-latest` can be updated without notice and is not recommended for production. Pin to a dated snapshot (e.g. `sonic-3`) for production traffic.
#### What to know to be successful
* **Spell tags still work the same way.** If you already wrap alphanumerics in `...`, you don't need to change anything — you'll just get better-sounding output. See [here](/build-with-cartesia/sonic-3-5/prompting-tips#controlling-pacing-and-spelling) for more details.
* **If you use custom delimiters** (commas/periods between characters or groups) to control pacing, our recommended format has changed. Use **spaces between characters** and **commas between groups**, e.g. `A B C, 1 2 3` instead of `A, B, C. 1, 2, 3.`. See [Prompting tips for Sonic 3.5](/build-with-cartesia/sonic-3-5/prompting-tips) for more details.
* **Speed and volume controls are temporarily disabled** on `sonic-3-latest`. If you rely on speed or volume augmentation (including via SSML), stay on `sonic-3` for now. We believe that Sonic 3.5 has more natural pacing and you may find that you don't need to use speed control as much when using this model.
* **Timestamps behave slightly differently.** If you use end-of-word timestamps for interruption handling, you should not see a meaningful change. If you depend on beginning-of-word timestamps, please test carefully and reach out if you see regressions for your use case.
* **Existing Professional Voice Clones (PVCs) do not carry over to `sonic-3-latest`.** Professional Voice Clones are pinned to the base model they were trained on (e.g. `sonic-3`) and will function as a standard voice clone for this model. For more information, see [Clone Voices (Pro)](/build-with-cartesia/capability-guides/clone-voices-pro/playground).
* **Providing proper context to the model improves naturalness.** Please see our buffering guide [here](/use-the-api/tts-websocket/buffering) for more details.
#### Where to look for help
* [Sonic 3.5 model overview](/build-with-cartesia/tts-models/sonic-3-5)
* [Prompting tips for Sonic 3.5](/build-with-cartesia/sonic-3-5/prompting-tips)
* [Model aliases and snapshots](/build-with-cartesia/tts-models/latest#continuous-updates-and-model-snapshots)
### API
* **Usage and API keys** — New HTTP APIs for **usage** and **API keys**.
* **Speech-to-text (STT)** — Improved documentation. See [STT streaming](/api-reference/stt/stt).
### Playground
* **Improved call details experience** — **Click on a transcript** to seek audio when reviewing calls.
* **Cancel call** — You can now **cancel active calls** from the Playground, for example, if you mistakenly made outbound calls.
* **Keys** — One **Keys** screen with **Standard** and **Admin** tabs when your org has access.
* **Pronunciation dictionaries** — In-app **list and detail** views for dictionaries tied to your organization.
### Line / Agents
* **LLM provider** — Agent inference paths standardize on **Anthropic**; setup copy and defaults no longer point voice agents at **Gemini** keys.
* **OpenAI WebSocket mode** — We now support OpenAI's WebSocket mode, which offers **low latency** for agent inference.
* **Transfer and end call interruption** — In the Line SDK, you can set **transfer** and **end call** as **uninterruptible**.
### Models / Voices
* **Voice Library** — **34** new voices across **10** locales (`ar-001`, `de-DE`, `en-US`, `en-AU`, `he-IL`, `hi-IN`, `ko-KR`, `tl-PH`, `ta-IN`, `te-IN`).
* **Voice cloning** — More reliable uploads for **M4A** (and similar) source clips when creating clones.
### Self-hosted
* **Playground** — Add voices to your on-prem deployment.
* **Pronunciation dictionaries** — **`POST /onprem/add-pdict`** to import dictionaries from cloud into self-hosted stacks.
* **STT** — Optional streaming STT via your **configured provider** integration in self-hosted environments.
### Breaking
* **Text-to-Agent (T2A) API** — Text-to-Agent workflow for Line is **deprecated**.
### API
* **Error responses** — For `Cartesia-Version: 2026-03-01`, we now return structured JSON. See [API Errors](/use-the-api/api-errors).
* API versions before `2026-03-01` continue to return legacy error formats (for example HTTP `Title: Message`).
* **Voices** — `PATCH /voices/{id}`: voice owners can now update accent and gender. Voice creation validates language. Invalid voice UUIDs and pronunciation-dictionary IDs return 404 instead of ambiguous errors.
* **PVC model routing** — PVC voices require a dated model ID (e.g. **`sonic-3-2026-01-12`**) instead of **`sonic-3`**. See [Clone Voices (Pro)](/build-with-cartesia/capability-guides/clone-voices-pro/api).
* **Voice search** — Name and metadata search is **diacritics-insensitive**.
### Playground
* **Pro voice clones**
* Clearer **language mismatch** messaging
* **Background noise removal** is now a simple on/off control
* **Fine-tuning model support**:
* Removed support for older models
* Now only **sonic-3-2026-01-12** is supported
* **Multilingual agents** — Multilingual agent configuration is now supported in the Playground.
* **Agents UI** — Search by **call ID** and **agent ID**.
### Billing
* **Concurrency** — Organizations can receive **notifications** when concurrency nears configured **limits**.
### Model / voice
* **Professional Voice Clones** — Backend updates improve stability of the professional voice cloning workflow.
* **Accents & filters** — Additional **accent** options (e.g. **Irish**, **New Zealand**, **South African**, **Belgian**) and **locale aliases** for accent filtering in APIs and Playground.
* **Voice Library** — **94** new voices across **17** locales (including Arabic, German, English variants, Spanish, Finnish, French, Hebrew, Hindi, Japanese, Korean, Polish, Portuguese, Swedish, Telugu, Thai, and more).
### Self-hosted
* **On-premises** — API for managing voices on self-hosted deployments.
### Cartesia SDK
* **cartesia-js v3.0.0** (Mar 2) — Major updates:
* New features: `flush_id` included in chunk and voice changer binary responses; `output_format` and infill support; inline WebSocket response types; byte endpoint returns **ArrayBuffer**; improved **WebPlayer** and client export.
* Fixes: memory leak and timing issues with abort signals/listeners, handling of empty `Content-Length`, and **TimeoutError** now includes a message.
See [cartesia-js releases](https://github.com/cartesia-ai/cartesia-js/releases) for full details.
### Line
* **[History Management API](/line/sdk/agents#history-management)**: You can add or replace the history provided to your agent, for example, to summarize a long conversation.
* **[Custom User Events](/line/sdk/events#custom-event)**: You can send bidirectional custom events between your client and the agent. You could use this, for example, if you have a web application with UI interactions.
* **[Uninterruptible Messages](/line/sdk/events#speech)**: You can set messages as uninterruptible. A common use case is a legal disclaimer at the beginning of a call.
* **End Tool Call Improvements**: The default end call tool call is more conservative to prevent calls from ending prematurely.
### API
* Increased reliability of API connections
### Cartesia SDK
* **cartesia-python v3.0.0** (Feb 9). See full details in [cartesia-python releases](https://github.com/cartesia-ai/cartesia-python/releases).
### Playground
* Shipped a new TTS page
* Shipped a new Voice Creation page
* Shipped a new Agents page
### Model changes
* **Improved pronunciation of real-world text patterns across languages**
* Enhanced support for structured and formatted speech patterns: numbers, dates, times, currency, phone numbers, IDs, percentages, and amounts/measurements.
* Support for various date formats (YYYY-MM-DD, YYYY/MM/DD, 年月日).
* Support for measurement units (meters, kg, tablespoon, gigabytes, etc.) with locale awareness.
* Support for domestic and international phone number formats with locale-specific chunking for French, Italian, German, Portuguese, Korean, and more.
* Improved alphanumeric ID handling with katakana/hiragana readings and Latin acronym transliteration to katakana for Japanese.
* Improves all languages except English, Hindi & other Indic languages, Arabic, Hebrew, Chinese, Swedish, Georgian, Bulgarian, and Tagalog (targeted for future updates).
* **Support for regional and locale-specific pronunciation within languages**
* Regional voices use region-specific terms in addition to accent (e.g. Belgian and Swiss French "nonante" vs. Canadian and French "quatre-vingt-dix").
* Region-specific number terminology, currency symbols, date formats, and measurement units.
* Locale-aware date and time formatting (e.g. Russian year suffixes, French/Spanish time conventions).
* Locale-aware currency symbol handling (e.g. \$ as "dollars" in en\_US and "pesos" in es\_MX).
* Locale pronunciation falls back to the primary country for that language (e.g. US for English, Brazil for Portuguese). We will continue to expand locale-aware support.
* Improves all languages except English, Hindi & other Indic languages, Arabic, Hebrew, Chinese, Swedish, Georgian, Bulgarian, and Tagalog (targeted for future updates). Existing regional pronunciation for English voices (e.g. British) is unaffected.
### Voice changes
* **Voice Library**: 39 new voices across 21 locales
### Breaking changes effective June 1, 2026
The following model snapshots and languages are discontinued effective June 1, 2026:
| Model | Snapshots | Languages |
| -------------------- | ---------------------------------------------------------------- | -------------------------- |
| `sonic` | All | All |
| `sonic-english` | — | All |
| `sonic-multilingual` | — | All |
| `sonic-2` | `sonic-2-2025-04-16`, `sonic-2-2025-05-08`, `sonic-2-2025-06-11` | it, nl, pl, ru, sv, tr, hi |
| | `sonic-2-2025-03-07` | All |
| `sonic-turbo` | `sonic-turbo-2025-06-04` | it, nl, pl, ru, sv, tr |
| | `sonic-turbo-2025-03-07` | All |
The following endpoints are discontinued effective June 1, 2026:
| Discontinued Endpoint | Replacement |
| ------------------------------------------ | ------------------------------------------ |
| Voice Embedding: `POST /voices/clone/clip` | [Clone Voice](/api-reference/voices/clone) |
| Mix Voices: `POST /voices/mix` | — |
| Create Voice: `POST /voices` | [Clone Voice](/api-reference/voices/clone) |
The following endpoints stop accepting voice embeddings effective June 1, 2026:
| Endpoint with a breaking change | Replacement |
| ------------------------------------- | ----------- |
| TTS (bytes): `POST /tts/bytes` | Voice ID |
| TTS (SSE): `POST /tts/sse` | Voice ID |
| TTS (WebSocket): `WSS /tts/websocket` | Voice ID |
### API
* **Regionalization** — Calls routed to US, EU, APAC by origin.
* **Parameterized outbound calls** — [Docs](/line/integrations/telephony/outbound-dialing)
* **Pronunciation dictionaries** — [Docs](/line/sdk/agents#custom-pronunciations)
### Model changes
* **Sonic-3 model versioning scheme introduced**
* New preview track: **`sonic-3-latest`** (continuous updates for early access and feedback).
* Stable track: **`sonic-3`** always points to the most recent stable release.
* Immutable dated snapshots: **`sonic-3-YYYY-MM-DD`** never change.
* Details: [Continuous updates and model snapshots](/build-with-cartesia/tts-models/latest#continuous-updates-and-model-snapshots)
* **Promotion to stable checkpoint:** **`sonic-3-2026-01-12`**
* Included improvements: consistent speed & volume, custom IPA pronunciations with stronger adherence, Hindi prosody improvements, Korean prosody/intonation improvements.
### Voice changes
* **Featured Voices launched** — Curated set of 30+ best-performing voices (e.g. [Cathy](https://play.cartesia.ai/voices/e8e5fffb-252c-436d-b842-8879b84445b6), [Henry](https://play.cartesia.ai/voices/87286a8d-7ea7-4235-a41a-dd9fa6630feb)).
* **Voice Library** — December: 25 new voices across 6 languages.
* **Voice Library** — January: 9 Spanish voices (Mexican, Colombian, Castilian).
### Playground
* Voice library usability improvements (test with your own scripts, call an agent per voice).
* One-click **Report Issue** on TTS Playground.
* Mini voice picker (recently used + saved) on TTS page.
* PVC UI + reliability (loading skeletons, error messages, better behavior with large datasets and silence).
### Line
* **Line SDK v0.2** — [Repo](https://github.com/cartesia-ai/line). Improved DX, long-running tool-call handling, **committed turns**, better turn-taking and transcription.