AdaptiVocab: Enhancing LLM Efficiency in Focused Domains through
  Lightweight Vocabulary Adaptation
Authors: name: Itay Nakash; name: Nitay Calderon; name: Eyal Ben David; name: Elad Hoffer; name: Roi Reichart
Published: 2025-03-25 14:18:21

Abstract: Large Language Models (LLMs) have shown impressive versatility as general
purpose models. However, their broad applicability comes at a high-cost
computational overhead, particularly in auto-regressive decoding where each
step requires a forward pass. In domain-specific settings, general-purpose
capabilities are unnecessary and can be exchanged for efficiency. In this work,
we take a novel perspective on domain adaptation, reducing latency and
computational costs by adapting the vocabulary to focused domains of interest.
We introduce AdaptiVocab, an end-to-end approach for vocabulary adaptation,
designed to enhance LLM efficiency in low-resource domains. AdaptiVocab can be
applied to any tokenizer and architecture, modifying the vocabulary by
replacing tokens with domain-specific n-gram-based tokens, thereby reducing the
number of tokens required for both input processing and output generation.
AdaptiVocab initializes new n-token embeddings using an exponentially weighted
combination of existing embeddings and employs a lightweight fine-tuning phase
that can be efficiently performed on a single GPU. We evaluate two 7B LLMs
across three niche domains, assessing efficiency, generation quality, and
end-task performance. Our results show that AdaptiVocab reduces token usage by
over 25% without compromising performance