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HerBERT is a BERT-based Language Model trained on Polish Corpora using only MLM objective with dynamic masking of whole words. For more details, please refer to: KLEJ: Comprehensive Benchmark for Polish Language Understanding.


HerBERT training dataset is a combination of several publicly available corpora for Polish language:

Corpus Tokens Texts
OSCAR 6710M 145M
Open Subtitles 1084M 1.1M
Wikipedia 260M 1.5M
Wolne Lektury 41M 5.5k
Allegro Articles 18M 33k


The training dataset was tokenized into subwords using HerBERT Tokenizer; a character level byte-pair encoding with a vocabulary size of 50k tokens. The tokenizer itself was trained on Wolne Lektury and a publicly available subset of National Corpus of Polish with a fastBPE library.

Tokenizer utilizes XLMTokenizer implementation for that reason, one should load it as allegro/herbert-klej-cased-tokenizer-v1.

HerBERT models summary

Model WWM Cased Tokenizer Vocab Size Batch Size Train Steps
herbert-klej-cased-v1 YES YES BPE 50K 570 180k

Model evaluation

HerBERT was evaluated on the KLEJ benchmark, publicly available set of nine evaluation tasks for the Polish language understanding. It had the best average performance and obtained the best results for three of them.

Model Average NKJP-NER CDSC-E CDSC-R CBD PolEmo2.0-IN\t PolEmo2.0-OUT DYK PSC AR\t
herbert-klej-cased-v1 80.5 92.7 92.5 91.9 50.3 89.2 76.3 52.1 95.3 84.5

Full leaderboard is available online.

HerBERT usage

Model training and experiments were conducted with transformers in version 2.0.

Example code:

from transformers import XLMTokenizer, RobertaModel

tokenizer = XLMTokenizer.from_pretrained("allegro/herbert-klej-cased-tokenizer-v1")
model = RobertaModel.from_pretrained("allegro/herbert-klej-cased-v1")

encoded_input = tokenizer.encode("Kto ma lepszą sztukę, ma lepszy rząd – to jasne.", return_tensors='pt')
outputs = model(encoded_input)

HerBERT can also be loaded using AutoTokenizer and AutoModel:

tokenizer = AutoTokenizer.from_pretrained("allegro/herbert-klej-cased-tokenizer-v1")
model = AutoModel.from_pretrained("allegro/herbert-klej-cased-v1")


CC BY-SA 4.0


If you use this model, please cite the following paper:

    title = "{KLEJ}: Comprehensive Benchmark for {P}olish Language Understanding",
    author = "Rybak, Piotr  and
      Mroczkowski, Robert  and
      Tracz, Janusz  and
      Gawlik, Ireneusz",
    booktitle = "Proceedings of the 58th Annual Meeting of the Association for Computational Linguistics",
    month = jul,
    year = "2020",
    address = "Online",
    publisher = "Association for Computational Linguistics",
    url = "https://www.aclweb.org/anthology/2020.acl-main.111",
    doi = "10.18653/v1/2020.acl-main.111",
    pages = "1191--1201",


The model was trained by Allegro Machine Learning Research team.

You can contact us at: klejbenchmark@allegro.pl

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