Sushant Kumar

Tokenization in Large Language Models

Table of Contents

  1. Introduction
  2. Vocabulary
  3. Tokenization Strategies


Tokenization is the process of breaking down a text into smaller units called tokens. These tokens can be words, subwords, or characters. Tokenization is a crucial step in Natural Language Processing (NLP) tasks, as it helps in converting text data into a format that can be used by machine learning models.


The set of unique tokens in a tokenizer is called the vocabulary. The vocabulary size is an important factor in tokenization, as it determines the number of unique tokens that the model can recognize and process. Large vocabularies can lead to memory and computational constraints, while small vocabularies may not capture the diversity of language effectively.

ModelVocabulary Size
Mistral - All models32,000

In the context of Large Language Models (LLMs) like BERT, GPT-2, and RoBERTa, tokenization plays a crucial role in converting raw text data into a format that the models can process and understand. The tokenization process is essential for several reasons:

  1. Vocabulary Size: Tokenization helps in reducing the vocabulary size by breaking down words into smaller units. This is particularly important in LLMs, where large vocabularies can lead to memory and computational constraints.

  2. Out-of-Vocabulary (OOV) Handling: Tokenization strategies like subword tokenization can handle rare and out-of-vocabulary terms effectively by breaking them down into subword units.

  3. Context Preservation: Tokenization ensures that the context of the text is preserved by representing words and phrases consistently across different documents.

  4. Model Interpretability: Tokenization impacts the interpretability of LLMs by influencing how the models process and represent text data. Different tokenization strategies can lead to variations in model performance and behavior.

In the context of LLMs, tokenization is a critical component of the Natural Language Processing (NLP) pipeline. It transforms raw text data into a format that can be used as input to the models, enabling them to learn patterns and relationships in the text.

Tokenization Strategies

The tokenization process involves converting raw text data into tokens that can be processed by machine learning models. There are several types of tokens that can be used in tokenization, including word, subword, and character tokens. Each type of token has its advantages and limitations, depending on the tokenization strategy used.

  • Word Tokenization: Word tokenization involves breaking down text into individual words based on whitespace or punctuation. While word tokenization is intuitive and easy to understand, it can lead to a large vocabulary size and may not handle rare or out-of-vocabulary terms effectively.

  • Subword Tokenization: Subword tokenization breaks down words into smaller subword units, such as prefixes, suffixes, and root words. This approach is effective in handling rare and out-of-vocabulary terms by representing them as combinations of subword units. Subword tokenization algorithms like Byte-Pair Encoding (BPE) and SentencePiece are commonly used in LLMs.

  • Character Token Tokenization: Character tokenization represents text as individual characters. While character tokenization can handle any input text, it may not capture higher-level linguistic patterns present in words and phrases.

Different tokenization strategies can lead to variations in the tokenized output, affecting the performance and interpretability of LLMs. The choice of tokenization strategy depends on factors such as the language of the text, the vocabulary size, and the computational resources available.