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Build Status Coverage Status Downloads Language grade: Python Code style: black License: GPL3


Fast Sentence Embeddings

Fast Sentence Embeddings is a Python library that serves as an addition to Gensim. This library is intended to compute sentence vectors for large collections of sentences or documents with as little hassle as possible:

from fse import Vectors, Average, IndexedList

vecs = Vectors.from_pretrained("glove-wiki-gigaword-50")
model = Average(vecs)

sentences = [["cat", "say", "meow"], ["dog", "say", "woof"]]


If you want to support fse, take a quick survey to improve it.


This package builds upon Gensim and is intenteded to compute sentence/paragraph vectors for large databases. Use this package if:

  • (Sentence) Transformers are too slow
  • Your dataset is too large for existing solutions (spacy)
  • Using GPUs is not an option.

The average (online) inference time for a well optimized (and batched) sentence-transformer is around 1ms-10ms per sentence. If that is not enough and you are willing to sacrifice a bit in terms of quality, this is your package.


Find the corresponding blog post(s) here (code may be outdated):

fse implements three algorithms for sentence embeddings. You can choose between unweighted sentence averages, smooth inverse frequency averages, and unsupervised smooth inverse frequency averages.

Key features of fse are:

[X] Up to 500.000 sentences / second (1)

[X] Provides HUB access to various pre-trained models for convenience

[X] Supports Average, SIF, and uSIF Embeddings

[X] Full support for Gensims Word2Vec and all other compatible classes

[X] Full support for Gensims FastText with out-of-vocabulary words

[X] Induction of word frequencies for pre-trained embeddings

[X] Incredibly fast Cython core routines

[X] Dedicated input file formats for easy usage (including disk streaming)

[X] Ram-to-disk training for large corpora

[X] Disk-to-disk training for even larger corpora

[X] Many fail-safe checks for easy usage

[X] Simple interface for developing your own models

[X] Extensive documentation of all functions

[X] Optimized Input Classes

(1) May vary significantly from system to system (i.e. by using swap memory) and processing. I regularly observe 300k-500k sentences/s for preprocessed data on my Macbook (2016). Visit Tutorial.ipynb for an example.


This software depends on NumPy, Scipy, Scikit-learn, Gensim, and Wordfreq. You must have them installed prior to installing fse.

As with gensim, it is also recommended you install a BLAS library before installing fse.

The simple way to install fse is:

pip install -U fse

In case you want to build from source, just run:

python install

If building the Cython extension fails (you will be notified), try:

pip install -U git+


Using pre-trained models with fse is easy. You can just use them from the hub and download them accordingly. They will be stored locally so you can re-use them later.

from fse import Vectors, Average, IndexedList
vecs = Vectors.from_pretrained("glove-wiki-gigaword-50")
model = Average(vecs)

sentences = [["cat", "say", "meow"], ["dog", "say", "woof"]]


If your vectors are large and you don't have a lot of RAM, you can supply the mmap argument as follows to read the vectors from disk instead of loading them into RAM:

Vectors.from_pretrained("glove-wiki-gigaword-50", mmap="r")

To check which vectors are on the hub, please check: For example, you will find:

  • glove-twitter-25
  • glove-twitter-50
  • glove-twitter-100
  • glove-twitter-200
  • glove-wiki-gigaword-100
  • glove-wiki-gigaword-300
  • word2vec-google-news-300
  • paragram-25
  • paranmt-300
  • paragram-300-sl999
  • paragram-300-ws353
  • fasttext-wiki-news-subwords-300
  • fasttext-crawl-subwords-300 (Use with FTVectors)

In order to use fse with a custom model you must first estimate a Gensim model which contains a gensim.models.keyedvectors.BaseKeyedVectors class, for example Word2Vec or Fasttext. Then you can proceed to compute sentence embeddings for a corpus as follows:

from gensim.models import FastText
sentences = [["cat", "say", "meow"], ["dog", "say", "woof"]]
ft = FastText(sentences, min_count=1, vector_size=10)

from fse import Average, IndexedList
model = Average(ft)

fse offers multi-thread support out of the box. However, for most applications a single thread will most likely be sufficient.

Additional Information

Within the folder nootebooks you can find the following guides:

Tutorial.ipynb offers a detailed walk-through of some of the most important functions fse has to offer.

STS-Benchmarks.ipynb contains an example of how to use the library with pre-trained models to replicate the STS Benchmark results [4] reported in the papers.

Speed Comparision.ipynb compares the speed between the numpy and the cython routines.

In order to use the fse model, you first need some pre-trained gensim word embedding model, which is then used by fse to compute the sentence embeddings.

After computing sentence embeddings, you can use them in supervised or unsupervised NLP applications, as they serve as a formidable baseline.

The models presented are based on

  • Deep-averaging embeddings [1]
  • Smooth inverse frequency embeddings [2]
  • Unsupervised smooth inverse frequency embeddings [3]

Credits to Radim Řehůřek and all contributors for the awesome library and code that Gensim provides. A whole lot of the code found in this lib is based on Gensim.

To install fse on Colab, check out:


Model Vectors  params STS Benchmark
CBOW paranmt-300 79.82
uSIF paranmt-300 length=11 79.00
SIF-10 paranmt-300 components=10 76.72
SIF-10 paragram-300-sl999 components=10 74.21
SIF-10 paragram-300-ws353 components=10 74.03
SIF-10 fasttext-crawl-subwords-300 components=10 73.38
uSIF paragram-300-sl999 length=11 73.04
SIF-10 fasttext-wiki-news-subwords-300 components=10 72.29
uSIF paragram-300-ws353 length=11 71.84
SIF-10 glove-twitter-200 components=10 71.62
SIF-10 glove-wiki-gigaword-300 components=10 71.35
SIF-10 word2vec-google-news-300 components=10 71.12
SIF-10 glove-wiki-gigaword-200 components=10 70.62
SIF-10 glove-twitter-100 components=10 69.65
uSIF fasttext-crawl-subwords-300 length=11 69.40
uSIF fasttext-wiki-news-subwords-300 length=11 68.63
SIF-10 glove-wiki-gigaword-100 components=10 68.34
uSIF glove-wiki-gigaword-300 length=11 67.60
uSIF glove-wiki-gigaword-200 length=11 67.11
uSIF word2vec-google-news-300 length=11 66.99
uSIF glove-twitter-200 length=11 66.67
SIF-10 glove-twitter-50 components=10 65.52
uSIF glove-wiki-gigaword-100 length=11 65.33
uSIF paragram-25 length=11 64.22
uSIF glove-twitter-100 length=11 64.13
SIF-10 glove-wiki-gigaword-50 components=10 64.11
uSIF glove-wiki-gigaword-50 length=11 62.06
CBOW word2vec-google-news-300 61.54
uSIF glove-twitter-50 length=11 60.41
SIF-10 paragram-25 components=10 59.07
uSIF glove-twitter-25 length=11 55.06
CBOW paragram-300-ws353 54.72
SIF-10 glove-twitter-25 components=10 54.16
CBOW paragram-300-sl999 51.46
CBOW fasttext-crawl-subwords-300 48.49
CBOW glove-wiki-gigaword-300 44.46
CBOW glove-wiki-gigaword-200 42.40
CBOW paragram-25 40.13
CBOW glove-wiki-gigaword-100 38.12
CBOW glove-wiki-gigaword-50 37.47
CBOW glove-twitter-200 34.94
CBOW glove-twitter-100 33.81
CBOW glove-twitter-50 30.78
CBOW glove-twitter-25 26.15
CBOW fasttext-wiki-news-subwords-300 26.08



  • Added support for gensim>=4. This library is no longer compatible with gensim<4. For migration, see the README.
  • size argument is now vector_size


  • Added Vectors and FTVectors class and hub support by from_pretrained
  • Extended benchmark
  • Fixed zero division bug for uSIF
  • Moved tests out of the main folder
  • Moved sts out of the main folder


  • Fixed dependency issue where you cannot install fse properly
  • Updated readme
  • Updated travis python versions (3.6, 3.9)

0.1.15 from 0.1.11:

  • Fixed major FT Ngram computation bug
  • Rewrote the input class. Turns out NamedTuple was pretty slow.
  • Added further unittests
  • Added documentation
  • Major speed improvements
  • Fixed division by zero for empty sentences
  • Fixed overflow when infer method is used with too many sentences
  • Fixed similar_by_sentence bug


  1. Iyyer M, Manjunatha V, Boyd-Graber J, Daumé III H (2015) Deep Unordered Composition Rivals Syntactic Methods for Text Classification. Proc. 53rd Annu. Meet. Assoc. Comput. Linguist. 7th Int. Jt. Conf. Nat. Lang. Process., 1681–1691.

  2. Arora S, Liang Y, Ma T (2017) A Simple but Tough-to-Beat Baseline for Sentence Embeddings. Int. Conf. Learn. Represent. (Toulon, France), 1–16.

  3. Ethayarajh K (2018) Unsupervised Random Walk Sentence Embeddings: A Strong but Simple Baseline. Proceedings of the 3rd Workshop on Representation Learning for NLP. (Toulon, France), 91–100.

  4. Eneko Agirre, Daniel Cer, Mona Diab, Iñigo Lopez-Gazpio, Lucia Specia. Semeval-2017 Task 1: Semantic Textual Similarity Multilingual and Crosslingual Focused Evaluation. Proceedings of SemEval 2017.


Disclaimer: I am working full time. Unfortunately, I have yet to find time to add all the features I'd like to see. Especially the API needs some overhaul and we need support for gensim 4.0.0.

I am looking for active contributors to keep this package alive. Please feel free to ping me at if you are interested.

Author: Oliver Borchers

Copyright (C) 2022 Oliver Borchers


If you found this software useful, please cite it in your publication.

	author = {Borchers, Oliver},
	title = {Fast sentence embeddings},
	year = {2019},
	publisher = {GitHub},
	journal = {GitHub Repository},
	howpublished = {\url{}},