KLASS: KL-Guided Fast Inference in Masked Diffusion Models (NeurIPS 2025 Spotlight)

🎉 Accepted at NeurIPS 2025 (Spotlight)

Authors: Seo Hyun Kim*, Sunwoo Hong*, Hojung Jung, Youngrok Park, Se-Young Yun
*Equal contribution

KLASS (KL-Adaptive Stability Sampling) is a fast inference method designed to accelerate generation in masked diffusion models while maintaining high-quality outputs.

This repository provides an implementation of KLASS on LLaDA 8B Instruct and Dream 7B Instruct, along with evaluation scripts for standard benchmarks including GSM8K, MATH, HumanEval, and MBPP.

🚀 Installation

1. Create and activate the conda environment:

   conda create -n klass python=3.12
   conda activate klass

2. Install dependencies and models:

   bash install.sh

   This script updates generation_utils.py in Dream with a customized version adapted for KLASS.

📊 Evaluation

We provide ready-to-run evaluation scripts for all supported models and datasets.

LLaDA

# GSM8K
bash scripts/llada_gsm8k.sh

# MATH
bash scripts/llada_math.sh

# Humaneval
bash scripts/llada_humaneval.sh

# MBPP
bash scripts/llada_mbpp.sh

Dream

# GSM8K
bash scripts/dream_gsm8k.sh

# MATH
bash scripts/dream_math.sh

# Humaneval
bash scripts/dream_humaneval.sh

# MBPP
bash scripts/dream_mbpp.sh

⚙️ Configuration & Arguments

You can customize the sampling behavior using the following arguments.

Main Sampling Algorithm

• alg: Choose the unmasking algorithm.
  • klass: Uses KLASS sampling, which unmask tokens based on a combination of confidence and KL-divergence stability.
  • default (for LLaDA) / maskgit_plus (for Dream): Top-K confidence-based unmasking.
  • random (for LLaDA) / origin (for Dream): Random unmasking order.

KLASS-Specific Parameters

These arguments are used only when alg="klass".

• conf_threshold: Filter out tokens with confidence lower than this value.
• kl_threshold: Filter out tokens with a KL score higher than this value (calculated over history_length).
• history_length: Number of recent steps to use for the KL divergence stability calculation.
• unmask_strategy: Defines the strategy for unmasking the tokens that satisfy both the confidence and KL thresholds:
  • all: Unmask all tokens that satisfy the thresholds. (Default)
  • max_conf: Among the tokens satisfying the thresholds, unmask only the one with the maximum confidence.
  • min_kl: Among the tokens satisfying the thresholds, unmask only the one with the minimum KL score.

Debugging

• save_steps: If set, this flag saves the detailed results of each generation step (including position, token ID, confidence, and KL divergence for all tokens) for analysis.

🙏 Acknowledgements

This codebase builds upon the official implementations of LLaDA, Dream, and HumanEval. We thank the original authors for their open-source contributions.