Paper Overview
Field: NLP Authors: Ryan Wang, Akshita Bhagia, Sewon Min Published: 2026-05-07 arXiv: 2605.06663
Abstract
Large language models are typically deployed as monolithic systems: even when an application only needs a narrow subset of capabilities such as code, math, or domain-specific knowledge, the full model must be loaded. Mixture of Experts (MoE) seemingly offers an alternative by activating only a subset of experts per input, but in practice, restricting inference to a domain-specific subset of experts severely degrades performance. This limits their usefulness in memory-constrained settings, especially as models grow larger and sparser.
We propose EMO, a Mixture of Experts designed for modularity — supporting independent use and composition of expert subsets without human-defined priors. Our core idea is to encourage tokens from similar domains to depend on similar experts. Since tokens within the same document typically share a domain, EMO constrains them to select experts from a shared pool, while allowing different documents to use different pools. This simple constraint, leveraging only document boundaries, induces coherent expert grouping during pretraining.
We pretrained a 1B-active-parameter, 14B-total-parameter EMO on 1T tokens. As a full model, it matches the performance of a standard MoE. Crucially, it enables selective expert usage: retaining only 25% (12.5%) of experts causes only 1% (3%) absolute performance degradation, whereas a standard MoE collapses in the same setting. We also find that expert subsets in EMO achieve semantic-level specialization (e.g., domains like math or code), in contrast to the low-level syntactic specialization observed in standard MoE.
Overall, our results demonstrate a path toward modular, memory-efficient deployment of large sparse models and open up new opportunities for composable architectures.
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