ESSA: Evolutionary Strategies for Scalable Alignment

Abstract: LLMs are increasingly relying on alignment techniques to ensure that their outputs match human preferences. Although reinforcement learning from human feedback (RLHF) is the dominant approach, it has high computational costs, memory requirements, and training instability, particularly when scaling to larger models. This paper introduces ESSA (Evolutionary Strategies for Scalable Alignment), a new framework that uses Evolutionary Strategies (ES) to efficiently align LLMs without the need for gradient computation. ES is well-suited for LLM alignment due to its favorable properties, such as high parallelizability, memory efficiency, robustness to sparse rewards, and fewer data samples required for convergence, especially when starting from a strong pre-trained policy. Moreover, ES eliminates the need for extensive hyperparameter tuning, making the alignment process simpler and more stable. Although ES excels in low-dimensional optimization, it poses a challenge when applied to high-dimensional LLMs. To address this challenge, we propose a parameter-efficient architectural modification that reduces the dimensionality of optimization through low-rank adaptation. We evaluated our approach on mathematical reasoning tasks with verifiable accuracy-based metrics, demonstrating that ESSA converges faster and is more data efficient than gradient-based methods like Group Relative Policy Optimization (GRPO). Our findings establish ES as a promising and scalable alternative to gradient-based alignment, paving the way for efficient post-training of LLMs.