# Kitten TTS 2

Powered by Stellon Labs.

`kitten_tts2` supports offline multilingual TTS, preset voices, reference-audio cloning,
and chunked long-form speech. The complete inference path is native C++/GGML:
Qwen3, S3 meanflow, HiFT, S3 tokenizer, CAMPPlus, and XVectorSincNet.
Python, LibTorch, TorchScript, and ONNX Runtime are not runtime dependencies.

The family is experimental; a compatible community GGUF is available below.
CPU and NVIDIA CUDA are validated. Other GPU backends, streaming, automatic
reference transcription, the upstream text normalizer, and the smaller
`student_w4`/`student_w8` decoders are not implemented or validated by this port.
The full default decoder is used.

## Build

Shared S3 code is included through the `chatterbox` dependency. No Kitten-specific
build flag or Torch package is needed.

This port uses the fixes from [Chatterbox S3 encoder correctness PR #778](https://github.com/0xShug0/audio.cpp/pull/778)
(relative-shift padding and attention/feed-forward LayerNorm epsilon), which
merged before the Kitten integration. Current upstream includes both changes.
The original Kitten integration also added build registration, documentation
indexes and the WebUI catalog with its generated bundle. The updated weight
profiles below update the Kitten implementation, exporter, package metadata, tests,
documentation and Kitten WebUI entries. CPU sessions also reuse exact-shape S3
encoder graphs; other S3Gen users retain their existing graph-release policy.

```sh
cmake -S . -B build-kitten2 -DAUDIOCPP_MODEL_SET=custom \
  -DAUDIOCPP_MODELS=kitten_tts2 -DENGINE_ENABLE_CUDA=OFF \
  -DENGINE_BUILD_MODEL_TESTS=ON
cmake --build build-kitten2 --config Release \
  --target audiocpp_cli audiocpp_server audiocpp_gguf audiocpp_kitten_tts2_prepare_voices --parallel 8
```

Visual Studio binaries are in `build-kitten2/bin/Release/`; single-configuration
builds use `build-kitten2/bin/`.
Run examples from the audio.cpp repository root and replace model/source path
placeholders with their actual locations. Commands use POSIX-shell `\` line
continuations; in PowerShell, join the lines or use backticks instead. Examples
using `audiocpp_cli` assume its binary directory is on `PATH`.

For NVIDIA, configure with `-DENGINE_ENABLE_CUDA=ON` and select
`--backend cuda` at runtime. The Kitten networks use the selected GGML backend;
reference resampling, sampling, and some small host computations remain on CPU.
Windows Release builds and preset/cloned speech were tested on a 16 GB RTX 4060 Ti
with CUDA Toolkit 13.3 and driver 610.88. Set `-DCMAKE_CUDA_ARCHITECTURES=89` when
building specifically for this card; choose the architecture for other cards.
CUDA 13.3 places its runtime DLLs in `CUDA_PATH/bin/x64`; ensure that directory
is on `PATH` when launching the executable on Windows.

The speaker's temporal max pooling uses a CUDA-supported 3x1 window. Inference
uses the existing backend precision and dispatch policy. For controlled CUDA
component comparisons, set `NVIDIA_TF32_OVERRIDE=0` before starting the native
probes, as described in the [test setup](../../tests/kitten_tts2/README.md).
This is a parity-test setting; ordinary synthesis is also tested without it.
See the [validation record](../../tests/kitten_tts2/validation.md)
for the current port's build, server/cloning checks, measured RTF and component
errors.

The WebUI shows **7 GB estimated VRAM** for the native Q8 package. An earlier
CUDA server run, before removing the shared precision edits, used a 238-character
passage and peaked approximately 4.7 GiB above the desktop baseline for preset
speech and 5.9 GiB for cloning. This measurement has not been repeated after
the cleanup. The estimate includes headroom; it is guidance, not a tested
minimum for every input or weight type.

## Download and preset speech

The refreshed [packages](https://huggingface.co/audio-cpp/audio.cpp-gguf/tree/main/KittenTTS2-GGUF)
contain the full native decoder, speaker encoders, and 124 prepared voice entries.
The checkpoint date in each filename distinguishes them from the older packages.
**Q8 is the default and recommended package**; Q4 preserves the BF16 embedding
and tied output head. Previous BF16 and hybrid Q4 packages remain available; see
[weight profiles](#updated-weight-profiles).

```sh
python tools/model_manager_v2.py install kitten_tts2 --models-root models
```

The family ID resolves to `kitten_tts2_20261021_q8_0`, which installs the GGUF
under `models/KittenTTS2-GGUF/`. No Hugging Face token is needed.

Direct download:
[kitten-tts2-20261021-q8_0.gguf](https://huggingface.co/audio-cpp/audio.cpp-gguf/resolve/main/KittenTTS2-GGUF/kitten-tts2-20261021-q8_0.gguf).
Separate model components or the original preset recordings are not needed at
runtime. Custom voice cloning still requires the reference clip and transcript
you supply.

```sh
audiocpp_cli --family kitten_tts2 \
  --model models/KittenTTS2-GGUF/kitten-tts2-20261021-q8_0.gguf \
  --backend cpu --threads 8 --task tts --voice-id Bruno \
  --request-option seed=1234 --text "Hello there. This is native Kitten speech." \
  --out hello.wav
```

### Upstream source assets

These assets are for direct safetensors loading, local conversion, or developer
validation. They are not additional downloads required by the published GGUF.

Use the upstream [KittenML/kitten-tts-2](https://huggingface.co/KittenML/kitten-tts-2)
layout, including the full `lm/model.safetensors`, LM configuration/tokenizer,
`config.json`, `cpp/default/voices.json`, and `speaker/model.safetensors`.
Preserve `LICENSE.md` and `speaker/LICENSE`.
For multilingual preset preparation, also keep `voices/voices.json` and its
referenced WAV/NPZ files. The upstream `cpp/default/decoder.pt` is needed only
for the optional PyTorch component comparisons described in the
[test guide](../../tests/kitten_tts2/README.md#validation-assets); the native
runtime and GGUF converter do not use it.

Add the official [S3 meanflow checkpoint](https://huggingface.co/ResembleAI/chatterbox-turbo/blob/main/s3gen_meanflow.safetensors)
as `native/s3gen_meanflow.safetensors`, and the
[Chatterbox MIT license](https://github.com/resemble-ai/chatterbox/blob/master/LICENSE)
as `native/LICENSE`. Validated decoder revision:
`749d1c1a46eb10492095d68fbcf55691ccf137cd`; SHA-256:
`d65cb687a2ed581ee6cc297e919ffefa63386944f42364ae13b78a594945514f`.
The runtime never downloads assets.

The upstream custom `cpp/model-tq2_1.gguf` and packed ternary/emb4 safetensors
are not inputs to this loader. Use the full safetensors or convert to audio.cpp GGUF.

```sh
audiocpp_cli --family kitten_tts2 --model /path/to/kitten-tts-2 \
  --backend cpu --threads 8 --task tts --voice-id Bruno \
  --request-option seed=1234 --text "Hello there. This is native Kitten speech." \
  --out hello.wav
```

The published v2 package contains 47 upstream voices and `PreparedBruno`.
Converting the current upstream checkpoint includes all 123 upstream voices and
the `PreparedBruno` alias. Select a voice present in the loaded package.
Output is mono 24 kHz audio, written with audio.cpp's existing WAV support.

## Languages

Use the language-named preset for Arabic, Chinese, French, German, Hindi,
Italian, Portuguese, Russian, or Spanish. The 38 named English voices remain
available in the published v2 package. Current upstream conversions additionally
include Dutch, Indonesian, Japanese, Korean, Polish, and Turkish presets, such as
`DutchBaker`, `IndonesianTourGuide`, `JapaneseTrainConductor`, `KoreanNewsAnchor`,
`PolishNewsAnchor`, and `TurkishNewsAnchor`.

```sh
audiocpp_cli --family kitten_tts2 --model models/kitten-tts2-v2/kitten-tts2-q8-v2-multilingual.gguf \
  --backend cpu --task tts --voice-id German \
  --text "Guten Morgen. Dies ist ein Test der deutschen Sprachausgabe." --out german.wav
```

The server accepts `"voice": "German"` (or another language preset) with UTF-8
text in `input`. A reference clip and transcript in the target language can also
be supplied for cloning. There is no separate language switch: the voice
reference supplies the accent and pronunciation context.

Text reaches the original Qwen tokenizer without English normalization, matching
upstream's recommendation to use `normalize=False` for other languages. Write
numbers, dates and abbreviations as spoken words in the target language.
The shared chunker preserves Unicode codepoints and supports CJK punctuation.

Upstream's README advertises 20 languages, but its published voice index provides
presets for English and the nine languages above. The remaining ten languages
have no shipped language presets in this snapshot and are not validated here.
Generation and tokenization checks do not establish pronunciation quality;
see the validation record for exactly what was exercised.

## Voice cloning

Supply a one-to-thirty-second reference clip and its transcript:

```sh
audiocpp_cli --family kitten_tts2 --model models/kitten-tts2-v2/kitten-tts2-q8-v2-multilingual.gguf \
  --backend cpu --threads 8 --task clon --voice-ref reference.wav \
  --reference-text "The exact words spoken in the reference clip." \
  --text "The new words to say in this voice." --request-option seed=1234 \
  --out cloned.wav
```

Cloning also works in TTS sessions. The C++ request accepts `voice.speaker.audio`
or `audio_input`, with `reference_text` in request options. Reference audio
takes precedence over a preset ID. The server speech endpoint accepts
`voice_ref` (path or base64) and `reference_text`.

Channels are averaged. Native sinc resampling supplies 16 kHz speaker/tokenizer
inputs and the 24 kHz decoder reference. The identity encoder uses the complete
clip. Decoder conditioning repeats short clips to at least six seconds and takes
at most ten seconds, following the upstream default decoder policy.
Upstream uses librosa/soxr for some S3 preprocessing, so reference tokens need not
be byte-identical with this native sinc resampler.

Reference encoders load on the first clone request. A session caches its last
clip and transcript; changing either invalidates conditioning and the LM prefix.
This in-memory cache does not register persistent voice IDs.

## Sampling and long-form text

Stable sampling defaults to temperature 0.8, top-p 0.8, top-k 50.
`preset=expressive` uses temperature/top-p 0.9. Explicit request options override
the preset; temperature zero selects greedy decoding.

The sampler uses the upstream 50-token repetition window, silence/end exemptions,
and token-run penalty. The tied head projects only speech codes and the two end
markers, deliberately excluding stray text tokens. Native RNG and arithmetic
differ from PyTorch CPU; equal seeds do not promise Python-identical waveforms.

Text defaults to 380-codepoint chunks in `tag_aware` mode. Each chunk reuses the
reference prefix and starts fresh target generation. Joins trim edge silence,
apply short fades, and insert 160 ms gaps. Expression tags reach the model
verbatim and enable its emotion prefix. Expand numbers/abbreviations when needed.

LM tensors retain their stored types by default. An explicit
`--session-option kitten_tts2.weight_type=...` changes projection storage only;
the embedding and tied output head retain their stored type. The decoder and
reference encoders use F32.

## CPU projection storage

The refreshed `kitten_tts2_20261021_q4_0` package stores Q4 projections directly,
with the BF16 embedding and output head preserved. Leave `weight_type` at
`native` to avoid runtime repacking.

For the published Q8-v2 GGUF or a current Q8 conversion, try
`--session-option kitten_tts2.weight_type=q4_0` on CPU. This packs the ternary
projection values exactly into Q4 blocks while retaining the stored BF16
embedding and output head. It is not the hybrid Q4 download, whose embedding is
also quantized. Repacking happens once when the session loads; it adds startup
work but reduces the cost of subsequent generation. The default remains
`native`, and the GGUF file is not modified.

```sh
audiocpp_cli --family kitten_tts2 \
  --model models/kitten-tts2-v2/kitten-tts2-q8-v2-multilingual.gguf \
  --backend cpu --threads 8 --task tts \
  --session-option kitten_tts2.weight_type=q4_0 \
  --request-option voice_id=Bruno --request-option seed=42 \
  --text "Please close the window before you leave. The books beside the desk must stay dry." \
  --out hello.wav --log
```

If output is cut short by the automatic token budget, set a larger ceiling,
for example `--request-option max_tokens=1000`.

## Execution plans

The default GGML path is unchanged. `kitten_tts2.exec_plan` is a session option;
existing GGUFs also accept it without reconversion. Components and parameters
omitted from the plan retain their defaults.

### NEON vocoder

Build with `-DENGINE_ENABLE_NEON=ON`, then select the HiFT neural decoder:

```sh
audiocpp_cli --task tts --family kitten_tts2 --model <model.gguf> \
  --backend cpu --threads 8 --text "Hello from Kitten TTS 2." \
  --session-option 'kitten_tts2.exec_plan={"vocoder":{"impl":"neon","backend":"cpu"}}' \
  --out output.wav --metrics --log
```

The same plan can be used with `--backend metal`: the rest of the model retains
Metal execution, while the HiFT convolution stack runs on the NEON CPU library.
Pitch prediction uses the existing framework API. Kitten keeps excitation
model-local and uses the existing STFT/ISTFT APIs for spectral processing.
The NEON library has no GGML dependency. Sampling settings, token budgets,
inference steps and language-model/flow execution remain unchanged.
Executor selection and weight adaptation stay in Kitten. The NEON path receives
plain mel/F0 arrays. The GGML HiFT module is unchanged.

## Updated weight profiles

Use the `kitten_tts2` model family and leave `kitten_tts2.weight_type` unset
(or select `native`) to retain the GGUF's stored precision. The loader reads
tensor types directly; no custom export selector is embedded in the package.
The WebUI sends no Kitten precision override by default.

| Export `--type` | Download filename | Source LM | Body / tied embedding | Approximate complete size |
| --- | --- | --- | --- | --- |
| `q8_0` | [kitten-tts2-20261021-q8_0.gguf](https://huggingface.co/audio-cpp/audio.cpp-gguf/resolve/main/KittenTTS2-GGUF/kitten-tts2-20261021-q8_0.gguf) | Refreshed ternary checkpoint | Q8_0 / BF16 | 3.34 GB |
| `q4_0 --embedding-type orig` | [kitten-tts2-20261021-q4_0.gguf](https://huggingface.co/audio-cpp/audio.cpp-gguf/resolve/main/KittenTTS2-GGUF/kitten-tts2-20261021-q4_0.gguf) | Refreshed BF16 checkpoint | Q4_0 / BF16 | 2.64 GB |
| `bf16` | [kitten-tts2-bf16-multilingual.gguf](https://huggingface.co/dignome/kitten_tts2/resolve/main/kitten-tts2-bf16-multilingual.gguf) | `model.safetensors` | BF16 / BF16 | 4.60 GB |
| `q8_0` | [kitten-tts2-q8-v2-multilingual.gguf](https://huggingface.co/dignome/kitten_tts2/resolve/main/kitten-tts2-q8-v2-multilingual.gguf) | `model-ternary.safetensors` | Q8_0 / BF16 | 3.28 GB |
| `q4_0` | [kitten-tts2-q4-multilingual.gguf](https://huggingface.co/dignome/kitten_tts2/resolve/main/kitten-tts2-q4-multilingual.gguf) | `model.safetensors` | Q4_0 / Q8_0 | 2.27 GB |

`install kitten_tts2` selects Q8. Install a selected package with:

```sh
python tools/model_manager_v2.py install kitten_tts2_bf16 --models-root models
python tools/model_manager_v2.py install kitten_tts2_20261021_q8_0 --models-root models
python tools/model_manager_v2.py install kitten_tts2_20261021_q4_0 --models-root models
python tools/model_manager_v2.py install kitten_tts2_q8_v2 --models-root models
python tools/model_manager_v2.py install kitten_tts2_q4 --models-root models
```

The three previous-checkpoint packages install into `models/kitten-tts2-v2/`, with distinct GGUF
filenames. They can coexist and share the license/NOTICE files. Select the
chosen GGUF path in the CLI/server. Each package also downloads `LICENSE`, `NOTICE`,
`native/LICENSE`, `speaker/LICENSE`, and `SHA256SUMS` from the same repository.

Every profile uses the existing default S3 MeanFlow decoder, reference encoders
and multilingual voice conditioning. No shared framework, S3 or ggml changes
are required. The student decoders and upstream TL2/emb4 format are not part of
these profiles.

The Q8 and Q4 body matrices preserve the updated BF16 checkpoint's ternary
values exactly in standard GGML blocks. Q4 is a mixed-precision export: its
embedding is quantized directly from full BF16 to Q8_0, with approximately
0.44% relative L2 weight error overall and 0.41% across speech-token rows.
These are reconstruction errors, not audio quality scores. Norms and speaker
projections retain BF16; S3 and reference components retain their original types.
Hybrid Q4 remains experimental: local ASR checks found missing words in longer
CPU samples. See the [validation record](../../tests/kitten_tts2/validation.md)
for speech-quality checks and limitations.

On CUDA, Q4 feed-forward down projections are loaded as BF16 to avoid
non-finite results with this model's large activations. Their values stay exact;
this adds about 483 MiB of resident weights compared with retaining those
projections as Q4. CPU keeps the Q4 body. File size is not a RAM/VRAM estimate.

Updated conversion requires NumPy, PyTorch and safetensors offline only.
The full `lm/model.safetensors` is needed for every updated profile to refresh
the preset speaker projections from the shipped NPZ identities. The existing
decoder conditioning and `PreparedBruno` alias are retained.

The exporter defaults to `--type q8_0`. Each type selects its source checkpoint
and tensor storage recipe, including the embedding precision shown above.
For exact Q4 projections with the original BF16 embedding and tied output head,
use `--type q4_0 --embedding-type orig`. This package loads directly with the
default native weight type, without runtime Q4 conversion.

For CPU-only ternary storage, `--type tq2_1` packs the 196 projections into
2.125 bits per weight, preserving independent scales for each 128-weight group.
The embedding/head stays BF16 and the codec stays F32. Load with native weight
storage; no session option is needed. This opt-in format requires an audio.cpp
binary with TQ2_1 support and is not a CUDA/Vulkan/Metal package. Existing package
defaults are unchanged. The CPU kernel is adapted from
[Kitten's C++ implementation](https://github.com/KittenML/kitten-tts-2-cpp).
audio.cpp uses GGUF type ID 44: the other fork's ID 43 is already used by
audio.cpp's I2_S format, so its ternary GGUFs are not interchangeable.

```sh
python tools/community_models/prepare_kitten_tts2_gguf.py \
  --model /path/to/updated-kitten-tts-2 --converter build-kitten2/bin/audiocpp_gguf \
  --type bf16 --output kitten-tts2-bf16-multilingual.gguf
python tools/community_models/prepare_kitten_tts2_gguf.py \
  --model /path/to/updated-kitten-tts-2 --converter build-kitten2/bin/audiocpp_gguf \
  --type q8_0 --output kitten-tts2-q8-v2-multilingual.gguf
python tools/community_models/prepare_kitten_tts2_gguf.py \
  --model /path/to/updated-kitten-tts-2 --converter build-kitten2/bin/audiocpp_gguf \
  --type q4_0 --output kitten-tts2-q4-multilingual.gguf
```

Use `--s3gen` and `--s3-license` when the original default decoder assets are
stored separately.

## Self-contained GGUF

The conversion commands above produce complete runtime packages. They require
the native converter and `audiocpp_kitten_tts2_prepare_voices` beside it.

The upstream prepared `cpp/default/voices.json` omits the nine language presets;
the helper fills those from `voices/voices.json`, the NPZ embeddings/tokens, and
reference WAVs. It refreshes every preset speaker projection with the updated
full LM while preserving decoder conditioning. These preparation dependencies
are not needed for inference.

Preparation uses CPU by default; `--voice-backend cuda` selects a CUDA-enabled
preparer. `--voice-preparer` can select an executable elsewhere. Save the complete
index with `--voices-output voices.json`, then reuse it with
`--prepared-voices voices.json` on later conversions. Incomplete indexes are
rejected so a multilingual spec cannot silently ship English-only voices.
For direct safetensors loading, install that complete index as
`MODEL/cpp/default/voices.json`; the original upstream index alone lacks the
language presets. The GGUF embeds it and needs no adjacent reference clips.

`--s3gen` and `--s3-license` can select assets outside the model directory.
All three tensor sources, preset conditioning, configuration, tokenizer, spec,
licenses, and NOTICE are packaged. No `.pt` file is embedded.
The package supports cloning without adjacent model files. Use the GGUF path as
`--model`.

Weights retain the [Stellon Labs Community License](https://huggingface.co/KittenML/kitten-tts-2/blob/main/LICENSE.md),
including commercial registration/limits and attribution requirements.
Decoder and speaker components retain their respective upstream terms.
No model weights are committed with the integration.

See [validation instructions](../../tests/kitten_tts2/README.md) and
[measured results](../../tests/kitten_tts2/validation.md).