Unchosen Experts Can Contribute Too: Unleashing MoE Models' Power by Self-Contrast

TL;DR

This paper introduces SCMoE, a simple and efficient method that leverages unchosen experts in MoE models through self-contrast during inference, significantly improving reasoning accuracy across multiple benchmarks.

Contribution

The paper proposes SCMoE, a training-free self-contrast strategy that utilizes unchosen experts in MoE models to enhance performance without additional training.

Findings

SCMoE improves GSM8K accuracy from 61.79 to 66.94.

SCMoE increases major@20 accuracy from 75.59 to 78.31.

Using unchosen experts via self-contrast enhances MoE model reasoning capabilities.

Abstract

Mixture-of-Experts (MoE) has emerged as a prominent architecture for scaling model size while maintaining computational efficiency. In MoE, each token in the input sequence activates a different subset of experts determined by a routing mechanism. However, the unchosen experts in MoE models do not contribute to the output, potentially leading to underutilization of the model's capacity. In this work, we first conduct exploratory studies to demonstrate that increasing the number of activated experts does not necessarily improve and can even degrade the output quality. Then, we show that output distributions from an MoE model using different routing strategies substantially differ, indicating that different experts do not always act synergistically. Motivated by these findings, we propose Self-Contrast Mixture-of-Experts (SCMoE), a training-free strategy that utilizes unchosen experts in a self-contrast manner during inference. In SCMoE, the next-token probabilities are determined by contrasting the outputs from strong and weak activation using the same MoE model. Our method is conceptually simple and computationally lightweight, as it incurs minimal latency compared to greedy decoding. Experiments on several benchmarks (GSM8K, StrategyQA, MBPP and HumanEval) demonstrate that SCMoE can consistently enhance Mixtral 8x7B's reasoning capability across various domains. For example, it improves the accuracy on GSM8K from 61.79 to 66.94. Moreover, combining SCMoE with self-consistency yields additional gains, increasing major@20 accuracy from 75.59 to 78.31.