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Zipformer-cr-ctc-transducer-XL-290M

Automatic Speech Recognition
K2
English
speech
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zipformer
transducer
cr-ctc
k2-fsa
offline-asr
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metadata 
language:
  - en
license: cc-by-nc-4.0
library_name: k2
pipeline_tag: automatic-speech-recognition
datasets:
  - esb/datasets
metrics:
  - wer
tags:
  - automatic-speech-recognition
  - speech
  - audio
  - zipformer
  - transducer
  - cr-ctc
  - k2-fsa
  - offline-asr

Zipformer-cr-ctc-transducer-XL-290M

Offline English ASR model based on the Icefall/K2 pruned transducer Zipformer-CR-CTC recipe. The model was trained with a transducer objective and CR-CTC (Consistency-Regularized CTC) auxiliary loss, and supports Icefall transducer and CTC decoding.

Files

  • model.pt: Zipformer CR-CTC transducer checkpoint
  • bpe.model: SentencePiece BPE model
  • tokens.txt: Icefall token table exported from bpe.model
  • config.yaml: model architecture, feature extraction, tokenizer, Zipformer model, decoding settings, and Hugging Face Hub download-metrics query file

Evaluation

Open ASR Leaderboard English short-form result, decoded with modified_beam_search and beam size 6:

Metric Value
Average WER 5.64
Parameters 288M

Dataset WERs:

Dataset WER
AMI 11.80
Earnings22 7.73
GigaSpeech 8.35
LibriSpeech Clean 1.29
LibriSpeech Other 3.03
SPGISpeech 1.65
VoxPopuli 5.64
Average 5.64

Training Data

The model was trained on a combined English training mixture built from the training portions of the datasets below.

Dataset Train Hours Source
LibriSpeech 960.0 ESB datasets
Earnings-22 105.0 ESB datasets
AMI Meeting Corpus 78.0 ESB datasets
Common Voice Scripted Speech 25.0 - English ~1,679.0 Mozilla Data Collective
Common Voice Spontaneous Speech 3.0 - English ~3.6 Mozilla Data Collective
GigaSpeech XL 10,000.0 ESB datasets
SPGISpeech 4,900.0 ESB datasets
TED-LIUM Release 3 454.0 ESB datasets
VoxPopuli 523.0 ESB datasets
Total ~18,700 ESB datasets and Mozilla Data Collective

Common Voice Scripted Speech 25.0 - English and Common Voice Spontaneous Speech 3.0 - English are the English scripted and spontaneous Common Voice releases checked on May 12, 2026.

For data normalization, the training transcripts were processed with direct LLM normalization using a self-hosted GLM-4.7 setup, plus custom agentic workflows built in collaboration with Claude Code 4.7 and Codex 5.4.

Training

The model was trained with the k2-fsa/Icefall framework, PyTorch 2.11, and CUDA 13.0 on 8 NVIDIA B300 GPUs using bf16 automatic mixed precision.

Usage With Icefall

From an Icefall checkout, download this model repo locally:

huggingface-cli download soundsgoodai/Zipformer-cr-ctc-transducer-XL-290M \
  --local-dir Zipformer-cr-ctc-transducer-XL-290M

Run offline decoding through Icefall. Input audio must already be 16 kHz:

cd icefall/egs/librispeech/ASR

PYTHONPATH=../../.. python zipformer/pretrained.py \
  --checkpoint /path/to/Zipformer-cr-ctc-transducer-XL-290M/model.pt \
  --tokens /path/to/Zipformer-cr-ctc-transducer-XL-290M/tokens.txt \
  --method modified_beam_search \
  --beam-size 6 \
  --num-encoder-layers "2,2,4,5,4,2" \
  --downsampling-factor "1,2,4,8,4,2" \
  --feedforward-dim "512,1024,2048,3072,2048,1024" \
  --num-heads "4,4,4,8,4,4" \
  --encoder-dim "192,384,768,1024,768,384" \
  --encoder-unmasked-dim "192,192,320,384,320,192" \
  --query-head-dim "32" \
  --value-head-dim "12" \
  --pos-head-dim "4" \
  --pos-dim 48 \
  --cnn-module-kernel "31,31,15,15,15,31" \
  --decoder-dim 512 \
  --joiner-dim 512 \
  --context-size 2 \
  --causal false \
  --chunk-size "16,32,64,-1" \
  --left-context-frames "64,128,256,-1" \
  --use-transducer true \
  --use-ctc true \
  --use-attention-decoder false \
  --use-cr-ctc true \
  /path/to/audio_1.wav \
  /path/to/audio_2.wav

For CTC decoding, use Icefall's CTC entrypoint with the same architecture settings:

cd icefall/egs/librispeech/ASR

PYTHONPATH=../../.. python zipformer/pretrained_ctc.py \
  --checkpoint /path/to/Zipformer-cr-ctc-transducer-XL-290M/model.pt \
  --tokens /path/to/Zipformer-cr-ctc-transducer-XL-290M/tokens.txt \
  --method ctc-decoding \
  --sample-rate 16000 \
  --num-encoder-layers "2,2,4,5,4,2" \
  --downsampling-factor "1,2,4,8,4,2" \
  --feedforward-dim "512,1024,2048,3072,2048,1024" \
  --num-heads "4,4,4,8,4,4" \
  --encoder-dim "192,384,768,1024,768,384" \
  --encoder-unmasked-dim "192,192,320,384,320,192" \
  --query-head-dim "32" \
  --value-head-dim "12" \
  --pos-head-dim "4" \
  --pos-dim 48 \
  --cnn-module-kernel "31,31,15,15,15,31" \
  --decoder-dim 512 \
  --joiner-dim 512 \
  --context-size 2 \
  --causal false \
  --chunk-size "16,32,64,-1" \
  --left-context-frames "64,128,256,-1" \
  --use-transducer true \
  --use-ctc true \
  --use-attention-decoder false \
  --use-cr-ctc true \
  /path/to/audio_1.wav \
  /path/to/audio_2.wav

The architecture and decoding values above are also recorded in config.yaml.

Decoding Methods

The model supports the following Icefall decoding methods:

Transducer:

  • greedy_search
  • modified_beam_search
  • fast_beam_search

CTC:

  • ctc-decoding

The reported Open ASR Leaderboard result uses modified_beam_search with beam size 6. CTC decoding is supported, but the table above does not report CTC WERs.

Feature Extraction And Resampling

For this model, use Kaldi-style fbank features. kaldifeat and kaldi-native-fbank are the recommended feature extraction backends.

Audio should be mono 16 kHz before feature extraction. For sample-rate conversion, audioop.ratecv is recommended because it matches the resampling path used for evaluation. On Python 3.13 and newer, use an audioop-compatible package such as audioop-lts.

Output Formatting

The model emits normalized English text with punctuation and capitalization. It does not automatically capitalize the first word of every sentence unless that word is normally capitalized, such as a proper noun, honorific, acronym, or similar named expression.

The model also normalizes common written forms, including numbers, dates, and currency, to digit-based forms.

Open ASR Leaderboard Evaluation

The open_asr_leaderboard/soundsgoodai runner downloads this model repo, resamples audio to 16 kHz with audioop, computes fbank features with kaldi-native-fbank, and decodes with Icefall modified_beam_search.

cd open_asr_leaderboard/soundsgoodai
bash run_zipformer.sh

Notes

  • The model expects 16 kHz mono audio.
  • The packaged leaderboard decoding configuration uses transducer modified_beam_search with beam size 6.
  • The checkpoint is an offline ASR model and is not intended for streaming decoding.
  • The checkpoint includes both transducer and CR-CTC heads, so Icefall loading should use --use-ctc true and --use-cr-ctc true.

References