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arxiv:2502.01618

A Probabilistic Inference Approach to Inference-Time Scaling of LLMs using Particle-Based Monte Carlo Methods

Published on Feb 3
· Submitted by akashsri on Feb 6
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Abstract

Large language models (LLMs) have achieved significant performance gains via scaling up model sizes and/or data. However, recent evidence suggests diminishing returns from such approaches, motivating scaling the computation spent at inference time. Existing inference-time scaling methods, usually with reward models, cast the task as a search problem, which tends to be vulnerable to reward hacking as a consequence of approximation errors in reward models. In this paper, we instead cast inference-time scaling as a probabilistic inference task and leverage sampling-based techniques to explore the typical set of the state distribution of a state-space model with an approximate likelihood, rather than optimize for its mode directly. We propose a novel inference-time scaling approach by adapting particle-based Monte Carlo methods to this task. Our empirical evaluation demonstrates that our methods have a 4-16x better scaling rate over our deterministic search counterparts on various challenging mathematical reasoning tasks. Using our approach, we show that Qwen2.5-Math-1.5B-Instruct can surpass GPT-4o accuracy in only 4 rollouts, while Qwen2.5-Math-7B-Instruct scales to o1 level accuracy in only 32 rollouts. Our work not only presents an effective method to inference-time scaling, but also connects the rich literature in probabilistic inference with inference-time scaling of LLMs to develop more robust algorithms in future work. Code and further information is available at https://probabilistic-inference-scaling.github.io.

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The paper "A Probabilistic Inference Approach to Inference-Time Scaling of LLMs using Particle-Based Monte Carlo Methods" presents a novel approach to improve the inference-time scaling of large language models (LLMs). Instead of relying on traditional deterministic optimization, which is often prone to reward hacking and diminishing returns, the paper proposes a probabilistic framework using particle-based Monte Carlo methods. This methodology allows for sampling from the "typical set" of a distribution, enabling robust scaling without directly optimizing for the mode of the reward function.

Unique Contributions and Relevance

  1. Breakthrough in Efficient Scaling:
    The method allows smaller LLMs to achieve performance comparable to larger models by dynamically allocating computational resources at inference time. For example, with only a few rollouts, smaller models demonstrated the ability to outperform state-of-the-art larger models like GPT-4o on challenging tasks. This indicates a pathway to reducing the carbon footprint and resource demands of AI by leveraging smarter algorithms rather than sheer size.

  2. Probabilistic Framework for Robustness:
    By focusing on probabilistic inference and exploring distributions effectively, the framework mitigates issues like overfitting to spurious patterns or reward hacking. It shifts the paradigm from deterministic search to probabilistic exploration, leading to more generalized and robust solutions.

  3. Mathematical and Cognitive Parallels:
    The paper connects the mechanics of machine learning to broader probabilistic reasoning frameworks, offering potential insights into how machines can simulate human-like adaptability and reasoning under uncertainty.

How It Helps Humanity Stay "Human"

  1. Ethical Machine Control:
    By focusing on probabilistic frameworks and rejecting reward hacking, the proposed method aligns machine behavior closer to human ethical reasoning systems, where decisions are rarely binary or deterministic.

  2. Empower Smaller Systems:
    The approach democratizes access to AI capabilities, reducing reliance on massive-scale computational infrastructure. This aligns with the humanist goal of making powerful tools accessible without monopolizing resources.

  3. Guardrails Against Misaligned AI:
    Probabilistic reasoning frameworks allow for more predictable and interpretable AI behavior, ensuring systems are more aligned with human values and reducing risks of uncontrollable outputs.

This framework underscores the importance of balancing computational efficiency, performance, and ethical considerations. Its methodology supports the creation of AI systems that not only perform well but remain under human control, reinforcing humanity’s role as the stewards of technology.

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