Wren-ASR-0.5B-multi

Multilingual automatic speech recognition model in the Wren series. Encodes audio with the Kyutai Mimi neural codec, then transcribes with a Qwen/Qwen2.5-0.5B backbone — no acoustic encoder, no CTC, just a small LLM consuming Mimi codes as input embeddings.

Supports 8 languages: English, German, French, Spanish, Dutch, Italian, Polish, Portuguese.

Architecture

audio ──► Mimi encoder (k=3) ──► Qwen2.5-0.5B (audio prefix → text) ──► transcript

Mimi codes serve as a discrete audio prefix in the LLM's input embedding space. At each audio frame the k=3 codebook codes go through k separate input embedding tables; their sum (scaled by 1/√k) is the input embedding for that step. The audio prefix is wrapped in <|audio_start|> / <|audio_end|> tokens, after which the LLM autoregressively emits text using its native vocabulary and lm_head — no new output heads were added.

Backbone: Qwen2.5-0.5B (causal LM; transformer body ~358M params, 151k-token multilingual vocab)
Audio tokenizer: Mimi (kyutai/mimi), 12.5 fps, 2048-entry codebooks
Codebooks used: first 3 (semantic-content-rich); reduces input embedding size 8/3× vs 8-codebook variants
Audio prefix: <|audio_start|> + summed-codebook embeds × T_frames + <|audio_end|>
Output: standard text autoregression via model.llm.generate(inputs_embeds=...)

Training data

Trained on the union of every dataset used to train Wren-TTS — the same 6 corpora that power the en/multi/expressive TTS recipes, with text used as the ASR target:

Dataset	Rows	Language(s)
VCTK	~44k	en (109 speakers, multiple accents)
Jenny	~21k	en (single speaker)
LibriTTS-R	~360k	en (clean_100 + clean_360 + other_500)
LJSpeech	~13k	en (single speaker)
MLS	~6.0M	de · fr · es · it · nl · pl · pt
Expresso (tagged)	~26k	en (style tags stripped at load time)
Total	~6.46M rows / epoch

Mimi codes are pre-extracted and published as the per-corpus mimi-codes datasets (see Datasets above) — no online encoding during training. Single-pass from-scratch training, ~k=3 codebooks. Held-out validation combines LibriTTS-R dev_clean + MLS dev (all 7 langs) + Expresso dev (tags stripped) + 5% per single-speaker English source. All weights set to 1.0 (every row, every epoch, no subsampling). Trained on a single A100-40GB.

Text casing and punctuation are preserved in the ground-truth transcripts.

Usage

pip install torch torchaudio transformers

import torch
import torchaudio
from transformers import AutoModel, AutoProcessor

model_id  = "shangeth/Wren-ASR-0.5B-multi"
device    = "cuda" if torch.cuda.is_available() else "cpu"

processor = AutoProcessor.from_pretrained(model_id, trust_remote_code=True)
model     = AutoModel.from_pretrained(model_id, trust_remote_code=True).to(device).eval()

# Load any short clip (one of the 8 supported languages, ≤ 30 s)
wav, sr = torchaudio.load("input.wav")

inputs = processor(audio=wav, sampling_rate=sr)
inputs = {k: v.to(device) for k, v in inputs.items()}

ids  = model.generate(**inputs, max_new_tokens=200)
text = processor.batch_decode(ids, skip_special_tokens=True)[0]
print(text)

Sampling tips

Defaults: greedy decoding (do_sample=False). For longer / harder utterances:

Pass do_sample=True, temperature=0.7, top_p=0.9 for diverse beams
Raise max_new_tokens if transcripts are getting cut off
Audio is hard-capped at 30 s (375 frames @ 12.5 fps) by the training recipe; for longer audio, segment first

Limitations & known issues

Language coverage: only the 8 trained languages. Out-of-distribution audio produces noise / hallucinated text in the closest matching language.
Per-language quality varies with data volume: German / Dutch / French are strongest (largest training shares); Polish / Portuguese / Italian have less training data and may be less accurate.
Audiobook-style audio dominates training: MLS / LibriTTS-R / LJSpeech / Jenny are all studio-style read speech. Performance on conversational audio, noisy environments, or accented far-field input may degrade.
0.5B backbone — quality is below frontier ASR systems (Whisper-large-v3, USM, etc.). The pitch is "small enough to run anywhere" + "shares architecture with Wren-TTS-0.5B-multi for unified speech-text experimentation".
30s audio cap. Hard-cap at training time; longer audio needs to be segmented externally.
No speaker diarization. Single-stream transcription only.

The Wren series

Wren is a family of compact (<3B parameter) multimodal speech LLMs — small enough to run on a single consumer GPU, designed for open research on unified speech understanding and synthesis.

Wren-TTS — text → speech (English + multilingual + expressive variants)
Wren-ASR — speech → text (this release)
Wren-LM — speech-language modelling / dialog (planned)
Wren-Omni — unified ASR + TTS + LM in one checkpoint (planned)

All Wren models share the same design principles: small backbone LLM + neural audio codec, open weights, simple PyTorch checkpoints, reproducible training recipes. Wren-ASR uses the same Qwen2.5-0.5B backbone as Wren-TTS-0.5B-multi and is trained on the same corpora — making the pair a natural starting point for unified speech-text modelling research.

Repository contents

File	Purpose
`model.safetensors`	Model weights
`config.json`	`WrenASRConfig` (with `auto_map` for `trust_remote_code`)
`tokenizer.json` + friends	Qwen2.5 tokenizer with Wren-ASR's 2 special tokens added
`processor_config.json`	`WrenASRProcessor` auto_map
`configuration_wren_asr.py`	`WrenASRConfig(PretrainedConfig)`
`modeling_wren_asr.py`	`WrenForASR(PreTrainedModel)` — loads Mimi codec lazily on first call
`processing_wren_asr.py`	`WrenASRProcessor(ProcessorMixin)` — audio → Mimi codes + text decode
`README.md`	This model card

Citation

@misc{wren2026,
  title  = {Wren: A Family of Small Open-Weight Models for Unified Speech-Text Modelling},
  author = {Shangeth Rajaa},
  year   = {2026},
  url    = {https://github.com/shangeth/wren}
}

License

Apache-2.0 for the checkpoint weights and code in this repo. Upstream components carry their own licenses — review before redistribution. The Expresso dataset (used for English style robustness) is CC-BY-NC-4.0; if you build derived models on this checkpoint and want to release them commercially, retrain with Expresso excluded.

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Safetensors

Model size

0.5B params

Tensor type

F32

BF16

shangeth
/

Wren-ASR-0.5B-multi