Provides guidance for LLM post-training with RL using slime, a Megatron+SGLang framework. Use when training GLM models, implementing custom data generation workflows, or needing tight Megatron-LM integration for RL scaling.
apm install @orchestra-research/slime-rl-training---
name: slime-rl-training
description: Provides guidance for LLM post-training with RL using slime, a Megatron+SGLang framework. Use when training GLM models, implementing custom data generation workflows, or needing tight Megatron-LM integration for RL scaling.
version: 1.0.0
author: Orchestra Research
license: MIT
tags: [Reinforcement Learning, Megatron-LM, SGLang, GRPO, Post-Training, GLM]
dependencies: [sglang-router>=0.2.3, ray, torch>=2.0.0, transformers>=4.40.0]
---
# slime: LLM Post-Training Framework for RL Scaling
slime is an LLM post-training framework from Tsinghua's THUDM team, powering GLM-4.5, GLM-4.6, and GLM-4.7. It connects Megatron-LM for training with SGLang for high-throughput rollout generation.
## When to Use slime
**Choose slime when you need:**
- Megatron-LM native training with SGLang inference
- Custom data generation workflows with flexible data buffers
- Training GLM, Qwen3, DeepSeek V3, or Llama 3 models
- Research-grade framework with production backing (Z.ai)
**Consider alternatives when:**
- You need enterprise-grade stability features → use **miles**
- You want flexible backend swapping → use **verl**
- You need PyTorch-native abstractions → use **torchforge**
## Key Features
- **Training**: Megatron-LM with full parallelism support (TP, PP, DP, SP)
- **Rollout**: SGLang-based high-throughput generation with router
- **Data Buffer**: Flexible prompt management and sample storage
- **Models**: GLM-4.x, Qwen3, DeepSeek V3/R1, Llama 3
## Architecture Overview
```
┌─────────────────────────────────────────────────────────┐
│ Data Buffer │
│ - Prompt initialization and management │
│ - Custom data generation and filtering │
│ - Rollout sample storage │
└─────────────┬───────────────────────────┬───────────────┘
│ │
┌─────────────▼───────────┐ ┌─────────────▼───────────────┐
│ Training (Megatron-LM) │ │ Rollout (SGLang + Router) │
│ - Actor model training │ │ - Response generation │
│ - Critic (optional) │ │ - Reward/verifier output │
│ - Weight sync to rollout│ │ - Multi-turn support │
└─────────────────────────┘ └─────────────────────────────┘
```
## Installation
```bash
# Recommended: Docker
docker pull slimerl/slime:latest
docker run --rm --gpus all --ipc=host --shm-size=16g \
-it slimerl/slime:latest /bin/bash
# Inside container
cd /root/slime && pip install -e . --no-deps
```
### From Source
```bash
git clone https://github.com/THUDM/slime.git
cd slime
pip install -r requirements.txt
pip install -e .
```
## Quick Start: GRPO Training
```bash
# Source model configuration
source scripts/models/qwen3-4B.sh
# Launch training
python train.py \
--actor-num-nodes 1 \
--actor-num-gpus-per-node 4 \
--rollout-num-gpus 4 \
--advantage-estimator grpo \
--use-kl-loss --kl-loss-coef 0.001 \
--rollout-batch-size 32 \
--n-samples-per-prompt 8 \
--global-batch-size 256 \
--num-rollout 3000 \
--prompt-data /path/to/data.jsonl \
${MODEL_ARGS[@]} ${CKPT_ARGS[@]}
```
---
## Workflow 1: Standard GRPO Training
Use this workflow for training reasoning models with group-relative advantages.
### Prerequisites Checklist
- [ ] Docker environment or Megatron-LM + SGLang installed
- [ ] Model checkpoint (HuggingFace or Megatron format)
- [ ] Training data in JSONL format
### Step 1: Prepare Data
```python
# data.jsonl format
{"prompt": "What is 2 + 2?", "label": "4"}
{"prompt": "Solve: 3x = 12", "label": "x = 4"}
```
Or with chat format:
```python
{
"prompt": [
{"role": "system", "content": "You are a math tutor."},
{"role": "user", "content": "What is 15 + 27?"}
],
"label": "42"
}
```
### Step 2: Configure Model
Choose a pre-configured model script:
```bash
# List available models
ls scripts/models/
# glm4-9B.sh, qwen3-4B.sh, qwen3-30B-A3B.sh, deepseek-v3.sh, llama3-8B.sh, ...
# Source your model
source scripts/models/qwen3-4B.sh
```
### Step 3: Launch Training
```bash
python train.py \
--actor-num-nodes 1 \
--actor-num-gpus-per-node 8 \
--rollout-num-gpus 8 \
--advantage-estimator grpo \
--use-kl-loss \
--kl-loss-coef 0.001 \
--prompt-data /path/to/train.jsonl \
--input-key prompt \
--label-key label \
--apply-chat-template \
--rollout-batch-size 32 \
--n-samples-per-prompt 8 \
--global-batch-size 256 \
--num-rollout 3000 \
--save-interval 100 \
--eval-interval 50 \
${MODEL_ARGS[@]}
```
### Step 4: Monitor Training
- [ ] Check TensorBoard: `tensorboard --logdir outputs/`
- [ ] Verify reward curves are increasing
- [ ] Monitor GPU utilization across nodes
---
## Workflow 2: Asynchronous Training
Use async mode for higher throughput by overlapping rollout and training.
### When to Use Async
- Large models with long generation times
- High GPU idle time in synchronous mode
- Sufficient memory for buffering
### Launch Async Training
```bash
python train_async.py \
--actor-num-nodes 1 \
--actor-num-gpus-per-node 8 \
--rollout-num-gpus 8 \
--advantage-estimator grpo \
--async-buffer-size 4 \
--prompt-data /path/to/train.jsonl \
${MODEL_ARGS[@]}
```
### Async-Specific Parameters
```bash
--async-buffer-size 4 # Number of rollouts to buffer
--update-weights-interval 2 # Sync weights every N rollouts
```
---
## Workflow 3: Multi-Turn Agentic Training
Use this workflow for training agents with tool use or multi-step reasoning.
### Prerequisites
- [ ] Custom generate function for multi-turn logic
- [ ] Tool/environment interface
### Step 1: Define Custom Generate Function
```python
# custom_generate.py
async def custom_generate(args, samples, evaluation=False):
"""Multi-turn generation with tool calling."""
for sample in samples:
conversation = sample.prompt
for turn in range(args.max_turns):
# Generate response
response = await generate_single(conversation)
# Check for tool call
tool_call = extract_tool_call(response)
if tool_call:
tool_result = execute_tool(tool_call)
conversation.append({"role": "assistant", "content": response})
conversation.append({"role": "tool", "content": tool_result})
else:
break
sample.response = response
sample.reward = compute_reward(sample)
return samples
```
### Step 2: Launch with Custom Function
```bash
python train.py \
--custom-generate-function-path custom_generate.py \
--max-turns 5 \
--prompt-data /path/to/agent_data.jsonl \
${MODEL_ARGS[@]}
```
See `examples/search-r1/` for a complete multi-turn search example.
---
## Configuration Reference
### Three Argument Categories
slime uses three types of arguments:
**1. Megatron Arguments** (passed directly):
```bash
--tensor-model-parallel-size 2
--pipeline-model-parallel-size 1
--num-layers 32
--hidden-size 4096
```
**2. SGLang Arguments** (prefixed with `--sglang-`):
```bash
--sglang-mem-fraction-static 0.8
--sglang-context-length 8192
--sglang-log-level INFO
```
**3. slime Arguments**:
```bash
# Resource allocation
--actor-num-nodes 1
--actor-num-gpus-per-node 8
--rollout-num-gpus 8
--colocate # Share GPUs between training/inference
# Data
--prompt-data /path/to/data.jsonl
--input-key prompt
--label-key label
# Training loop
--num-rollout 3000
--rollout-batch-size 32
--n-samples-per-prompt 8
--global-batch-size 256
# Algorithm
--advantage-estimator grpo # or: gspo, ppo, reinforce_plus_plus
--use-kl-loss
--kl-loss-coef 0.001
```
### Key Constraints
```
rollout_batch_size × n_samples_per_prompt = global_batch_size × num_steps_per_rollout
```
Example: 32 × 8 = 256 × 1
---
## Data Buffer System
slime's data buffer enables flexible data management:
### Basic Data Source
```python
class RolloutDataSource:
def get_samples(self, num_samples):
"""Fetch prompts from dataset."""
return self.dataset.sample(num_samples)
def add_samples(self, samples):
"""Called after generation (no-op by default)."""
pass
```
### Buffered Data Source (Off-Policy)
```python
class RolloutDataSourceWithBuffer(RolloutDataSource):
def __init__(self):
self.buffer = []
def add_samples(self, samples):
"""Store generated samples for reuse."""
self.buffer.extend(samples)
def buffer_filter(self, args, buffer, num_samples):
"""Custom selection logic (prioritized, stratified, etc.)."""
return select_best(buffer, num_samples)
```
---
## Common Issues and Solutions
### Issue: SGLang Engine Crash
**Symptoms**: Inference engine dies mid-training
**Solutions**:
```bash
# Enable fault tolerance
--use-fault-tolerance
# Increase memory allocation
--sglang-mem-fraction-static 0.85
# Reduce batch size
--rollout-batch-size 16
```
### Issue: Weight Sync Timeout
**Symptoms**: Training hangs after rollout
**Solutions**:
```bash
# Increase sync interval
--update-weights-interval 5
# Use colocated mode (no network transfer)
--colocate
```
### Issue: OOM During Training
**Symptoms**: CUDA OOM in backward pass
**Solutions**:
```bash
# Enable gradient checkpointing
--recompute-activations
# Reduce micro-batch size
--micro-batch-size 1
# Enable sequence parallelism
--sequence-parallel
```
### Issue: Slow Data Loading
**Symptoms**: GPU idle during data fetch
**Solutions**:
```bash
# Increase data workers
--num-data-workers 4
# Use streaming dataset
--streaming-data
```
---
## Supported Models
| Model Family | Configurations |
|--------------|----------------|
| GLM | GLM-4.5, GLM-4.6, GLM-4.7, GLM-Z1-9B |
| Qwen | Qwen3 (4B, 8B, 30B-A3B), Qwen3-MoE, Qwen2.5 |
| DeepSeek | V3, V3.1, R1 |
| Llama | Llama 3 (8B, 70B) |
| Others | Kimi K2, Moonlight-16B |
Each model has pre-configured scripts in `scripts/models/`.
---
## Advanced Topics
### Co-location Mode
Share GPUs between training and inference to reduce memory:
```bash
python train.py \
--colocate \
--actor-num-gpus-per-node 8 \
--sglang-mem-fraction-static 0.4 \
${MODEL_ARGS[@]}
```
### Custom Reward Model
```python
# custom_rm.py
class CustomRewardModel:
def __init__(self, model_path):
self.model = load_model(model_path)
def compute_reward(self, prompts, responses):
inputs = self.tokenize(prompts, responses)
scores = self.model(inputs)
return scores.tolist()
```
```bash
--custom-rm-path custom_rm.py
```
### Evaluation Multi-Task
```bash
--eval-prompt-data aime /path/to/aime.jsonl \
--eval-prompt-data gsm8k /path/to/gsm8k.jsonl \
--n-samples-per-eval-prompt 16
```
---
## Resources
- **Documentation**: https://thudm.github.io/slime/
- **GitHub**: https://github.com/THUDM/slime
- **Blog**: https://lmsys.org/blog/2025-07-09-slime/
- **Examples**: See `examples/` directory for 14+ worked examples