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FLARE: Diffusion for Hybrid Language Model
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Presents FLARE, a recipe converting hybrid softmax+linear-attention Qwen3.5 AR checkpoints into diffusion LLMs (2B/4B/9B) via a clean/noisy two-stream loss, with hardware-aware recurrent-state kernels and a unified AR-Trust/Diffusion-Trust serving stack.
Problem
AR-to-diffusion LLM conversion often loses the seed model's capability, and it is unclear how to make diffusion training and serving efficient on hybrid-attention (softmax plus linear-attention) backbones under a limited training budget.
Approach
Jointly train a causal clean stream (next-token loss) and a block-bidirectional noisy stream (two complementary masked views, token-balanced loss) with a document-packed mask; realize noisy-block visibility on GDN layers via recurrent-state handoff from clean block-boundary states rather than dense masking, and serve both verified speculative (AR-Trust) and parallel denoising (Diffusion-Trust) fro
Key results
- FLARE-9B (AR-Trust) reaches 95.20 on MATH-500 vs 96.60 for Qwen3.5-9B and 49.71 on LiveCodeBench v6, exceeding LLaDA-2.1-flash on GPQA-Diamond (71.21 vs 66.67).
- On a single A100-80GB at concurrency 8, FLARE-2B reaches 2,087 tokens/s on GSM8K, a 2.2x gain over LLaDA-2.1-mini.
- Training MFU of FLARE-2B at B=4 on 8xA100 rises to 24.81%, slightly above the AR Qwen3.5-2B reference (24.04%).
Surprising findings
- Diffusion-Trust decoding is consistently weaker on code generation than AR-Trust, which the authors attribute partly to answer-extraction and truncation issues.
- Automatic IFD-based data filtering does not close the residual gap to the source AR model.
Limitations
- Training roughly doubles per-step compute and memory because clean and noisy views are concatenated into a 2L input.
- Residual gap to the source Qwen3.5 AR checkpoints on instruction following and some coding benchmarks.
- Validated only on dense models under 10B parameters with a single SFT stage; MoE and RL post-training untested.
Experimental setup
Datasets: Llama-Nemotron-Post-Training Nemotron-Math-Proofs-v1 Nemotron-Cascade-1/-2-SFT-Data Nemotron-Instruction-Following-Chat-v1/v2 Nemotron-Post-Training-Dataset-v2 GSM8K MATH-500 AIME 24/25 ARC-Challenge GPQA-Diamond MMLU MMLU-Pro
Benchmarks: GSM8K MATH-500 AIME 24 AIME 25 ARC-Challenge GPQA-Diamond MMLU MMLU-Pro IFEval HumanEval MBPP LiveCodeBench v6
Metrics: accuracy pass@1 tokens per second MFU
Baselines: Mercury-2 LLaDA-2.0-mini LLaDA-2.1-mini LLaDA-2.0-flash LLaDA-2.1-flash SDAR-30B-A3B SDAR-1.7B SDAR-4B SDAR-8B Qwen3.5
Builds on: Gated DeltaNet Qwen3.5 BD3-LM SDAR TiDAR I-DLM
Closest papers by meaning
- SimSD: Simple Speculative Decoding in Diffusion Language Models (NeurIPS 2026 · similarity 0.89)
- Accelerating Diffusion LLMs via Adaptive Parallel Decoding (NeurIPS 2025 · similarity 0.89)
- Polestar: Drift-Aware Cache Calibration and Token Commitment for Efficient Inference of Diffusion LLMs (NeurIPS 2026 · similarity 0.88)
- Fast and Fluent Diffusion Language Models via Convolutional Decoding and Rejective Fine-tuning (NeurIPS 2025 · similarity 0.88)
- When Linear Attention Meets Autoregressive Decoding: Towards More Effective and Efficient Linearized Large Language Models (ICML 2024 · similarity 0.88)
- DAWN: Dependency-Aware Fast Inference for Diffusion LLMs (NeurIPS 2026 · similarity 0.88)
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