Research map / Image generation / Fast diffusion sampling
ELF: Embedded Language Flows
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Proposes ELF, a continuous-time flow matching diffusion language model that denoises in frozen T5 embedding space with a shared-weight final decoding step, adding training-time CFG and self-conditioning.
Problem
Continuous diffusion language models lag discrete DLMs; it is unclear whether the gap stems from the discrete nature of language or from algorithmic design choices, and existing continuous DLMs use per-step token-level losses or separate decoders.
Approach
Perform flow matching entirely in a frozen pretrained contextual embedding space (x-prediction, rectified flow), discretizing only at the final time step with a shared-weight network trained with cross-entropy, so no separate decoder is needed and image-style CFG can be applied directly via training-time CFG with self-conditioning.
Key results
- ELF-B reaches generative perplexity 24 on OWT with 32 sampling steps (SDE sampler, self-conditioning CFG 3), with 105M parameters versus ~170M for baselines.
- ELF-B achieves 26.4 BLEU on WMT14 De-En and 36.0 ROUGE-1 on XSum, best among compared methods of similar scale.
- ELF uses about 45B training tokens versus over 500B for prior DLMs; ELF+PD distillation reaches 21.32 Gen. PPL at 32 steps and 136.10 at 1 step.
Surprising findings
- v-prediction works poorly when weights are shared with the final discretization step, so x-prediction is needed.
- Shared-weight denoiser-decoder matches a separately trained two-stage decoder and extends further toward low generative perplexity.
Limitations
- Performance degrades with very few sampling steps (1-4 steps) without distillation.
- Evaluation uses generative perplexity under GPT-2 Large, which is an imperfect quality proxy; no validation perplexity reported for likelihood.
Experimental setup
Datasets: OpenWebText WMT14 German-English XSum
Benchmarks: OpenWebText WMT14 De-En XSum
Metrics: generative perplexity unigram entropy BLEU ROUGE-1 ROUGE-2 ROUGE-L
Baselines: MDLM Duo FLM LangFlow E2D2 CDCD SeqDiffuSeq MDLM+SDTT Duo+DCD FMLM AR
Builds on: Flow Matching rectified flow classifier-free guidance self-conditioning Muon optimizer progressive distillation
Closest papers by meaning
- LangFlow: Continuous Diffusion Rivals Discrete in Language Modeling (NeurIPS 2026 · similarity 0.92)
- Flow Map Language Models: One-step Language Modeling via Continuous Denoising (NeurIPS 2026 · similarity 0.90)
- Simple and Effective Masked Diffusion Language Models (NeurIPS 2024 · similarity 0.88)
- Continuous Latent Diffusion Language Model (NeurIPS 2026 · similarity 0.87)
- Rare Text Semantics Were Always There in Your Diffusion Transformer (NeurIPS 2025 · similarity 0.87)
- Discrete Modeling via Boundary Conditional Diffusion Processes (NeurIPS 2024 · similarity 0.87)
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