--- license: apache-2.0 language: - en metrics: - accuracy base_model: - Qwen/Qwen2.5-3B-Base pipeline_tag: reinforcement-learning tags: - Search - QuestionAnswering library_name: transformers ---

On GRPO Collapse in Search-R1: The Lazy Likelihood-Displacement Death Spiral

📃 Paper |🤗 LLDS-Huggingface |🐙 GitHub

## ⚡ Introduction **LLDS** is a lightweight likelihood-preserving regularization designed to stabilize **tool-integrated reinforcement learning** (e.g., GRPO / Search-R1 style training). It prevents training collapse by regularizing **only when** the likelihood of (good) action decreases, and **only on** the tokens responsible for the decrease. - We identify **Lazy Likelihood Displacement (LLD)** as a key mechanism behind collapse in tool-integrated GRPO training. - LLDS activates **selectively**: it penalizes likelihood reduction on a *preserving set* (e.g., non-negative-advantage actions). - We release our **LLDS-tuned Qwen2.5-3B-Base** checkpoint for searchs-integrated reasoning and QA. - **A refer to action-level gate**, R refer to response-level gate, **action (A) level gate achieve the best performance**. ## 🔍 Tool-Integrated Search Inference (Search-R1 style) We support tool-integrated inference using the same workflow as **[Search-R1](https://github.com/PeterGriffinJin/Search-R1)**, where the LLM interacts with a local retrieval server for multi-step reasoning. The pipeline consists of two parts: 1. Launch a local retriever server 2. Run inference with the LLDS model --- ### 1️⃣ Launch the local retrieval server Search-R1 recommends running the retriever in a separate environment. ```bash conda activate retriever bash retrieval_launch.sh ``` ### 2️⃣ Run inference with LLDS-R-GRPO-Qwen2.5-3B-Base ```bash conda activate searchr1 python infer.py MODEL_NAME = "/" # e.g. my-org/LLDS-R-GRPO-Qwen2.5-3B-Base question = "Your question here" ``` ## 📖 Citation ``` @article{deng2025grpo, title={On GRPO Collapse in Search-R1: The Lazy Likelihood-Displacement Death Spiral}, author={Deng, Wenlong and Li, Yushu and Gong, Boying and Ren, Yi and Thrampoulidis, Christos and Li, Xiaoxiao}, journal={arXiv preprint arXiv:2512.04220}, year={2025} } ```