Diffusion vs. Autoregressive Language Models: A Text Embedding
  Perspective
Authors: name: Siyue Zhang; name: Yilun Zhao; name: Liyuan Geng; name: Arman Cohan; name: Anh Tuan Luu; name: Chen Zhao
Published: 2025-05-21 02:59:14

Abstract: Large language model (LLM)-based embedding models, benefiting from large
scale pre-training and post-training, have begun to surpass BERT and T5-based
models on general-purpose text embedding tasks such as document retrieval.
However, a fundamental limitation of LLM embeddings lies in the unidirectional
attention used during autoregressive pre-training, which misaligns with the
bidirectional nature of text embedding tasks. To this end, We propose adopting
diffusion language models for text embeddings, motivated by their inherent
bidirectional architecture and recent success in matching or surpassing LLMs
especially on reasoning tasks. We present the first systematic study of the
diffusion language embedding model, which outperforms the LLM-based embedding
model by 20% on long-document retrieval, 8% on reasoning-intensive retrieval,
2% on instruction-following retrieval, and achieve competitive performance on
traditional text embedding benchmarks. Our analysis verifies that bidirectional
attention is crucial for encoding global context in long and complex text.