Model reference · open weights

diar_streaming_sortformer_4spk

diar_streaming_sortformer_4spk is an open-weight audio or speech model from nvidia, listed in the AxForge catalogue. AxForge can bring it up on EU-owned hardware for you on request — with the licence handled where one is required.

Licence fee required Audio nvidia 1 variants 39k downloads/mo
Request a licence + hosting quote All served models Not on the shared API today — deployed on request.

About

What diar_streaming_sortformer_4spk is

Streaming Sortformer Diarizer 4spk v2.1 img { display: inline; } [](#model-architecture) This model is a streaming version of Sortformer diarizer. Sortformer[1] is a novel end-to-end neural model for speaker diarization, trained with unconventional objectives compared to existing end-to-end diarization models. Streaming Sortformer[2] employs an Arrival-Order Speaker Cache (AOSC) to store frame-level acoustic embeddings of previously observed speakers. Sortformer resolves permutation problem in diarization following the arrival-time order of the speech segments from each speaker. This speaker diarization model can be used to enable the NeMo Voice Agent to recognize speakers in conversations. See the NeMo Voice Agent and the YAML configuration for more details. Discover more from NVIDIA: For documentation, deployment guides, enterprise-ready APIs, and the latest open models—including Nemotron and other cutting-edge speech, translation, and generative AI—visit the NVIDIA Developer Portal at developer.nvidia.com. Join the community to access tools, support, and resources to accelerate your development with NVIDIA’s NeMo, Riva, NIM, and foundation models.<br Explore more from NVIDIA: <br What is Nemotron?<br NVIDIA Developer Nemotron<br NVIDIA Riva Speech<br NeMo Documentation<br Model Architecture Streaming sortformer employs pre-encode layer in the Fast-Conformer to generate speaker-cache. At each step, speaker cache is filtered to only retain the high-quality speaker cache vectors. Aside from speaker-cache management part, streaming Sortformer follows the architecture of the offline version of Sortformer. Sortformer consists of an L-size (17 layers) [NeMo Encoder for Speech Tasks (NEST)](https://arxiv.org/abs/2408.13106)[3] which is based on Fast-Conformer[4] encoder. Following that, an 18-layer Transformer[5] encoder with hidden size of 192, and two feedforward layers with 4 sigmoid outputs for each frame input at the top layer. More information can be found in the Streaming Sortformer paper[2]. NVIDIA NeMo To train, fine-tune or perform diarization with Sortformer, you will need to install NVIDIA NeMo[6]. We recommend you install it after you've installed Cython

Summarised from the published model card. Read the full card on the HuggingFace links below.

Specifications

What it is

Makernvidia
TypeAudio & music
Variants1
Runs withnemo
Released2025-10-22
Popularity39k downloads / month
Likes100
LicenceCommercial licence needed

How it works

How audio & music work

Audio or textinputAudio modelrecognise / synthesiseText or audiooutputSpeech-to-text turns audio into text; text-to-speech and music models turn text into audio.

Variants

Sizes & precisions

Open weights ship in several sizes and precisions. One page, all the variants — pick the one that fits your GPU. VRAM figures are estimates from model size.

VariantParamsPrecisionVRAMFits 16 GBWeights
diar_streaming_sortformer_4spk-v2.1BF16Weights ↗

Benchmarks

Reported results

As published on the model card — the maker's own numbers, not measured by AxForge.

TaskDatasetMetricScore
Speaker DiarizationDIHARD III Eval (1-4 spk)Test DER15.09
Speaker DiarizationDIHARD III Eval (5-9 spk)Test DER41.42
Speaker DiarizationDIHARD III Eval (full)Test DER20.21
Speaker DiarizationCALLHOME (NIST-SRE-2000 Disc8) part2 (2 spk)Test DER6.65
Speaker DiarizationCALLHOME (NIST-SRE-2000 Disc8) part2 (3 spk)Test DER11.25
Speaker DiarizationCALLHOME (NIST-SRE-2000 Disc8) part2 (4 spk)Test DER13.35
Speaker DiarizationCALLHOME (NIST-SRE-2000 Disc8) part2 (5 spk)Test DER22.12
Speaker DiarizationCALLHOME (NIST-SRE-2000 Disc8) part2 (6 spk)Test DER24.51
Speaker DiarizationCALLHOME (NIST-SRE-2000 Disc8) part2 (full)Test DER11.19
Speaker Diarizationcall_home_american_english_speechTest DER5.09
Speaker DiarizationAliMeeting Test nearTest DER12.6
Speaker DiarizationAliMeeting Test farTest DER15.6
Speaker DiarizationAMI Test IHMTest DER16.67
Speaker DiarizationAMI Test SDMTest DER20.57
Speaker DiarizationNOTSOFAR1 Eval SC (<=4 spk)Test DER17.26
Speaker DiarizationNOTSOFAR1 Eval SC (>=5 spk)Test DER36.76
Speaker DiarizationNOTSOFAR1 Eval SC (full)Test DER28.75

Using it via the API

Call it like any OpenAI endpoint

Once AxForge deploys diar-streaming-sortformer-4spk for you, it answers on the OpenAI-compatible API — the same base URL and keys as every other model. (diar-streaming-sortformer-4spk below is illustrative; you get the exact model name on deployment.)

$ curl -sS https://api.axforge.ai/v1/audio/transcriptions \
  -H "Authorization: Bearer $AXFORGE_API_KEY" \
  -F model="diar-streaming-sortformer-4spk" -F file=@audio.mp3

Details

Languages, data & research

Trained / evaluated on

fisher_english NIST_SRE_2004-2010 librispeech ami_meeting_corpus voxconverse_v0.3 icsi aishell4 dihard_challenge-3-dev NIST_SRE_2000-Disc8_split1 NOTSOFAR1 Alimeeting-train DiPCo

Tags

nemo speaker-diarization speaker-recognition speech audio Transformer FastConformer Conformer NEST pytorch NeMo automatic-speech-recognition dataset:fisher_english dataset:NIST_SRE_2004-2010

Papers

Licence

Commercial licence needed

The weights are open but its licence needs a commercial agreement for business use. AxForge can arrange that licence and host the model for you — you pay AxForge, we settle with the model’s maker. Ask us for a quote. Read the licence ↗

Sources

Weights & code

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