ChatLearn: A flexible and efficient reinforcement learning framework for large language models(LLMs)

Introduction

ChatLearn is a large-scale reinforcement learning training framework for LLMs developed by the Alibaba Cloud PAI platform.

RLHF Flow

Chatlearn has the following advantages:

  1. 🚀User-friendly programming interface: Users can focus on programming individual models by wrapping a few functions, while the system takes care of resource scheduling, data and control flow transmission, and distributed execution.

  2. 🔧Highly Scalable Training Methodology: ChatLearn supports user-defined model execution flows, making customized training processes more flexible and convenient.

  3. 🔄Diverse Distributed Acceleration Engines: ChatLearn supports industry-leading SOTA training (FSDP2, Megatron) and inference engines (vLLM, SGLang), delivering exceptional training throughput performance.

  4. 🎯Flexible Parallel Strategies and Resource Allocation: ChatLearn supports different parallel strategies for various model configurations, enabling the formulation of distinct parallel approaches tailored to each model’s computational, memory, and communication characteristics. Additionally, ChatLearn features a flexible resource scheduling mechanism that accommodates exclusive or shared use of resources across models. Through its system scheduling policies, it facilitates efficient serial/parallel execution and optimized GPU memory sharing, enhancing overall performance and efficiency.

  5. ⚡High performance: Compared to current SOTA systems, ChatLearn achieves a 52% performance improvement at the 7B+7B (Policy+Reward) scale and a 137% performance improvement at the 70B+70B scale. Meanwhile, ChatLearn supports reinforcement learning training at scales exceeding 600B parameters.

Quick Start

Please refer to the documentation for a quick start.

  1. Environment and Code Setup

  2. End-to-End GRPO Training Pipeline for Qwen3 Model Using FSDP + vLLM

  3. End-to-End GRPO Training Pipeline for Qwen3 Model Using Megatron + vLLM

Feature List

  • Supports training engines such as Megatron and FSDP

  • Supports inference engines including vLLM and SGLang, controlled via the runtime_args.rollout_engine parameter

  • Supports reinforcement learning algorithms such as GRPO and GSPO

  • Supports experiment monitoring with wandb and tensorboard

  • Supports training acceleration techniques such as sequence packing, Ulysses sequence parallelism, and Group GEMM

Performance

We compared the RLHF training throughput of models with different parameter scales, adopting an N+N model configuration where both the Policy model and the Reward model have the same number of parameters. We benchmarked against DeepSpeed-Chat and OpenRLHF with 7B and 70B model configurations. For the 8 GPU setup with a 7B+7B scale, we achieved a 115% speedup; for the 32 GPU setup with a 70B+70B scale, the speedup was 208%. The larger the scale, the more pronounced the acceleration effect becomes. Additionally, ChatLearn can support even larger-scale reinforcement learning, such as at a 600B scale.

compare perf

Note: The performance of DeepSpeed-Chat and OpenRLHF has already been optimized.

Roadmap

The upcoming features for ChatLearn include:

  • Simplify Configuration Settings
  • Support tutorials for the RL training of MoE (Mixture of Experts) models
  • Support for more models
  • Performance Optimization
  • Support for more RL algorithms