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Karpathy's nanochat uses simplified GRPO for RL loop

Andrej Karpathy's nanochat project includes a simplified reinforcement learning loop, labeled GRPO, that deviates from the standard GRPO algorithm. This loop uses a basic policy gradient method, essentially REINFORCE with a mean baseline, to improve model performance on tasks with machine-checkable rewards like GSM8K. The simplified approach, which omits safety rails found in the full GRPO recipe, focuses on adjusting the model's output based on the average score of a batch, rather than relying on a separate critic or complex reward modeling. AI

IMPACT Demonstrates how simplified RL techniques can be effective for tasks with machine-checkable rewards, potentially lowering the barrier to training advanced models.

RANK_REASON The item discusses a simplified implementation of a reinforcement learning algorithm (GRPO) within a specific project (nanochat), detailing its technical aspects and comparison to established methods. [lever_c_demoted from research: ic=1 ai=1.0]

Read on dev.to — LLM tag →

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Karpathy's nanochat uses simplified GRPO for RL loop

COVERAGE [1]

  1. dev.to — LLM tag TIER_1 English(EN) · Ken Imoto ·

    nanochat + GRPO: I Read Karpathy's 300-Line RL Loop So You Don't Have To

    <p>Karpathy published <a href="https://github.com/karpathy/nanochat" rel="noopener noreferrer">nanochat on October 13, 2025</a>. Four hours on an 8×H100 node, roughly $100 of cloud spend, a ChatGPT-shaped model with a web UI at the end of it. The bit that got the least attention …