arXiv Computation and Language

Measuring Optimal Transport in Transformer Depth

The study investigates whether transformer models transport token representations across layers in a manner consistent with optimal transport theory. Using Pythia-160m and Pythia-410m, the authors measure exact assignments between consecutive layer clouds, calibrate couplings, and decompose the transport cost into common shifts and token‑specific moves. Results show that at the final layer both models align closely with the optimal‑transport map—Pythia‑410m at optimal cost and Pythia‑160m slightly above—while earlier layers deviate, and the agreement improves with training.

arXiv Computer Vision
2d ago

We Have Been Interpreting Diffusion Transformer Backbone Behaviors Wrong

The paper revisits the interpretation of depth profiles in Diffusion Transformer backbones, showing that the commonly observed inverted‑U curve reflects the influence of the prediction target (e.g., ε, u, x0) rather than a simple shift from coarse to fine semantic granularity. It argues that the semantically meaningful signal is merely an intermediate by‑product of predicting the target, and that different training setups—particularly the choice of prediction target—predictably alter the curve’s shape. The authors demonstrate how this new understanding can guide the optimal placement of REPA modules and provide code for further exploration.

By Benyuan Meng, Longtao Huang, Yang Liu, Liang Lin
arXiv AI
Jul 16

DeepLoop: Depth Scaling for Looped Transformers

arXiv:2607. 13491v1 Announce Type: cross Abstract: Looped Transformers scale sequential computation by applying a compact stack of physical blocks for multiple rounds, increasing unrolled depth without increasing stored parameters.

By Shuzhen Li, Yifan Zhang, Jiacheng Guo, Quanquan Gu, Mengdi Wang
arXiv AI
Jun 17

Rethinking Cross-Layer Information Routing in Diffusion Transformers

arXiv:2605. 20708v2 Announce Type: replace-cross Abstract: Diffusion Transformers (DiTs) have become a de facto backbone of modern visual generation, and nearly every major axis of their design -- tokenization, attention, conditioning, objectives, and latent autoencoders -- has been extensively revisited.

By Chao Xu, Maohua Li, Qirui Li, Yixuan Xu, Yanke Zhou, Yunhe Li, Cuifeng Shen, Hanlin Tang, Kan Liu, Tao Lan, Lin Qu, Shao-Qun Zhang
arXiv Machine Learning
Oct 22

Generalization and Scaling Laws for Mixture-of-Experts Transformers

The paper presents a theoretical framework for understanding generalization and scaling in Mixture-of-Experts (MoE) Transformers. It derives a sup‑norm covering‑number bound that separates active per‑input capacity from routing combinatorics, leading to a generalization bound under a manifold data model. Additionally, a constructive approximation theorem shows how error can be reduced by scaling active capacity or increasing the number of experts, from which neural scaling laws and compute‑optimal tradeoffs are derived.

By Mansour Zoubeirou a Mayaki
arXiv Machine Learning
Sep 22

Optimizers for Diffusion Models: A Controlled Benchmark

The paper introduces the first controlled benchmark for optimizers in discrete diffusion models, evaluating seven optimizers (AdamW, Lion, Muon, SOAP, MARS, MARS‑M, Schedule‑Free) across four diffusion formulations: masked diffusion on text8, uniform diffusion on QM9 and LM1B, and Gaussian diffusion on CelebA‑64. Each optimizer undergoes the same search protocol and is retrained with full budget and multiple seeds, revealing that AdamW, while strong, is not universally optimal and that optimizers validated on autoregressive language models (Muon, MARS‑M, SOAP) can outperform tuned AdamW on certain tasks.

By Arman Bolatov, Egor Shulgin, David Li, Abduragim Shtanchaev, Sebastian U. Stich, Maxim Panov, Eric Moulines, Peter Richt\'arik, Martin Tak\'a\v{c}
arXiv Machine Learning
Oct 3

Learning Rate Transfer for Hybrid Transformer-SSM Architectures

arXiv:2610. 01172v1 Announce Type: new Abstract: We study learning rate (LR) scaling for hybrid architectures combining Transformer and State-Space Model (SSM) blocks, a class adopted by several recent production language models.

By Jimin Seo, Gyubok Lee, Yeonsik Jo, Kiwoong Yoo, Yeongoon Kim, Minhae Oh, Jin Woo Koo, Suhwan Kim, Nakyung Lee, Minsik Seol, Idris Nechnech, Jaehyeon Kim, Giho Lee, Jungwoo Lee