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The Optimal Token Baseline: Variance Reduction for Long-Horizon LLM-RL
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The Optimal Token Baseline: Variance Reduction for Long-Horizon LLM-RL

#Large Language Models #Reinforcement Learning #Gradient Variance #Token Baseline #Training Stability #arXiv #AI Research

📌 Key Takeaways

  • Researchers developed a new 'Optimal Token Baseline' to solve the issue of training collapse in Large Language Models.
  • The method targets exploding gradient variance, which typically destabilizes Reinforcement Learning in long-horizon tasks.
  • Traditional value models and group-based baselines are criticized for failing to account for sequence heterogeneity.
  • The new framework allows for more stable optimization, potentially improving the reasoning capabilities of generative AI.

📖 Full Retelling

A team of AI researchers published a new technical paper on arXiv on February 12, 2025, introducing 'The Optimal Token Baseline,' a novel framework designed to prevent training collapse in Large Language Models (LLMs) during complex Reinforcement Learning (RL) tasks. The research addresses a critical technical bottleneck where models struggle to learn effectively over long horizons due to exploding gradient variance, a phenomenon that often leads to unstable training cycles and poor model performance. By reimagining baseline computation at the token level, the authors aim to stabilize the optimization process for the next generation of generative AI models. At the core of the problem is the difficulty in calculating 'advantage'—the metric used to determine how much better a specific action is compared to the average. Traditionally, RL for LLMs has relied on value models or group-based baselines to manage this calculation. However, the researchers argue that these standard methods are flawed because they often overlook sequence heterogeneity, meaning they fail to account for the diverse and varying nature of data within a single long string of text. While classic theory offers a path toward global variance reduction, current implementations remain difficult to optimize in real-world, high-scale environments. The 'Optimal Token Baseline' shifts the focus from broad group averages to a more granular approach. This method seeks to achieve a significant reduction in gradient variance by applying specific mathematical corrections at the token level, rather than the sequence level. This advancement is particularly relevant for training LLMs on tasks that require long-term reasoning, code generation, or complex multi-step instructions, where a single error early in a sequence can traditionally cause the entire learning process to deviate or collapse entirely.

🏷️ Themes

Artificial Intelligence, Machine Learning, Optimization

📚 Related People & Topics

Large language model

Type of machine learning model

A large language model (LLM) is a language model trained with self-supervised machine learning on a vast amount of text, designed for natural language processing tasks, especially language generation. The largest and most capable LLMs are generative pre-trained transformers (GPTs) that provide the c...

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Reinforcement learning

Reinforcement learning

Field of machine learning

In machine learning and optimal control, reinforcement learning (RL) is concerned with how an intelligent agent should take actions in a dynamic environment in order to maximize a reward signal. Reinforcement learning is one of the three basic machine learning paradigms, alongside supervised learnin...

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📄 Original Source Content
arXiv:2602.07078v1 Announce Type: cross Abstract: Reinforcement Learning (RL) for Large Language Models (LLMs) often suffers from training collapse in long-horizon tasks due to exploding gradient variance. To mitigate this, a baseline is commonly introduced for advantage computation; however, traditional value models remain difficult to optimize, and standard group-based baselines overlook sequence heterogeneity. Although classic optimal baseline theory can achieve global variance reduction, it

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