arXiv AI

Limitations on Autoregressive Token Generation via Sequential Sampling

arXiv Machine Learning
Sep 25

Enabling Approximate Joint Sampling in Diffusion LMs

The paper introduces a lightweight single‑layer sampler that allows masked diffusion language models to approximate joint sampling of multiple tokens in a single full‑model forward pass. By training the sampler to mimic exact joint sampling from a frozen diffusion model, the authors enable parallel unmasking of tokens while maintaining a close match to the true joint distribution. Experiments on Dream‑7B and Llada‑7B models show that unmasking four tokens per denoising step yields a MAUVE score of 0.87, a substantial improvement over the marginal baseline of 0.31.

By Parikshit Bansal, Sujay Sanghavi
arXiv Machine Learning
Oct 2

Fork-dLLM: Avoiding the Flexibility Trap in Diffusion Language Models

The paper introduces Fork-dLLM, a hybrid sampling strategy for diffusion language models that combines parallel token generation with autoregressive ordering only at uncertain fallback steps, thereby avoiding the flexibility trap that reduces generation diversity. It also presents ForkGRPO, an extension that applies the GRPO objective selectively during post‑training rollouts, preserving policy‑likelihood ratios while cutting rollout and optimization costs. Experiments show Fork-dLLM achieves pass@k scaling comparable to autoregressive sampling but 2–3× more efficient, and ForkGRPO matches or surpasses AR‑based GRPO baselines at significantly lower training expense.

By Stipe Frkovi\'c, Metod Jazbec, Christian A. Naesseth
arXiv Computation and Language
1d ago

SpecCTMC: Exact Speculative Simulation of Diffusion Language Model Continuous-Time Markov Chains

SpecCTMC is a training‑free speculative sampler for masked diffusion language models that reduces the sequential bottleneck of exact continuous‑time sampling. It updates tokens successively using previously computed predictions, evaluates intermediate states in parallel, and applies an exact acceptance‑and‑correction step, thereby preserving the joint distribution of event times, generation order, and token values. Experiments on LLaDA‑8B‑Instruct and Dream‑v0‑Instruct‑7B show 1.73‑4.38× fewer sequential model evaluations while maintaining the reference sampling distribution.

By Siva Rajesh Kasa, Yasong Dai, Sumit Negi, Hongdong Li