Is There a Case for Conversation Optimized Tokenizers in Large Language
  Models?
Authors: name: Raquel Ferrando; name: Javier Conde; name: Gonzalo Martínez; name: Pedro Reviriego
Published: 2025-06-23 14:18:46

Abstract: The computational and energy costs of Large Language Models (LLMs) have
increased exponentially driven by the growing model sizes and the massive
adoption of LLMs by hundreds of millions of users. The unit cost of an LLM is
the computation of a token. Therefore, the tokenizer plays an important role in
the efficiency of a model, and they are carefully optimized to minimize the
number of tokens for the text in their training corpus. One of the most popular
applications of LLMs are chatbots that interact with users. A key observation
is that, for those chatbots, what is important is the performance of the
tokenizer in the user text input and the chatbot responses. Those are most
likely different from the text in the training corpus. So, a question that
immediately arises is whether there is a potential benefit in optimizing
tokenizers for chatbot conversations. In this paper, this idea is explored for
different tokenizers by using a publicly available corpus of chatbot
conversations to redesign their vocabularies and evaluate their performance in
this domain. The results show that conversation-optimized tokenizers
consistently reduce the number of tokens in chatbot dialogues, which can lead
to meaningful energy savings, in the range of 5% to 10% while having minimal or
even slightly positive impact on tokenization efficiency for the original
training corpus.