Understanding Tokens in Large Language Models: A Complete Guide to GenAI Developers
As generative AI continues to evolve and integrate into various applications, developers in the GenAI field need a solid understanding of fundamental concepts, one of which is the “token.” In this blog post, we’ll delve into what tokens are, how they are calculated, and how language model providers, like OpenAI, count them. This knowledge is crucial not only for effective model training and tuning but also for managing operational costs.
What is a Token?
n the realm of language models, particularly those like GPT-3 and GPT-4, a token is not merely a word. It represents a piece of text, which could be a word, part of a word, or even punctuation. Tokens are the basic units of text that language models process. The process of breaking down text into tokens is called “tokenization.”
How are Tokens Calculated?
Tokenization might sound straightforward, but it’s a nuanced process influenced by the specific language model and its training. Here’s a general outline of how tokens are typically calculated:
1. Pre-processing: Initial text cleanup includes converting to lowercase, removing extra spaces, and sometimes standardizing text (like turning “don’t” into “do not”).
2. Breaking Down: The text is split into manageable pieces. For English, this often starts with words and punctuation.
3. Sub-tokenization: Larger words or complex entities might be further broken down into smaller units. For example, the word “unbelievable” might be split into “un”, “believ”, and “able”.
How Do Language Model Providers Count Tokens?
Each language model provider has its specific method for counting tokens, which is critical for developers to understand, especially for cost management in cloud-based language model APIs. Here’s how some of the major players do it:
1. OpenAI: For models like ChatGPT (based on GPT-3 or GPT-4), OpenAI counts tokens by considering each token as a piece of a word or punctuation as defined by their tokenizer. The input and output tokens are counted together towards the limit per request.
2. Google’s BERT and similar models: Tokenization involves WordPiece or SentencePiece models, which break down words into more predictable sub-units. Each piece counts as a token.
3. Meta’s RoBERTa: Uses a byte-level BPE tokenizer which means it breaks words down to a more granular level, and each byte-level piece counts as a token.
Practical Implications for Developers