arXiv Machine Learning

Bayesian Wind Tunnels for Model Selection

arXiv:2607. 19379v1 Announce Type: new Abstract: Prior work has shown that transformers can perform exact Bayesian filtering within a fixed hypothesis class.

arXiv Machine Learning
Jun 24

LLMs are Bayesian, In Expectation, Not in Realization

arXiv:2507. 11768v3 Announce Type: replace-cross Abstract: Bayesian accounts of in-context learning face a direct objection: exact posterior predictives for exchangeable data are invariant to task-preserving order, yet transformers change next-token probabilities when the same examples are serialized differently.

By Leon Chlon, Fatima Sheaib, Zein Khamis, Maggie Chlon, Mahdi El Zein, MarcAntonio M. Awada
arXiv AI
Sep 7

Unifying ICL, SFT, KL-Regularized RL Through a Bayesian Lens

The paper presents a Bayesian framework that unifies several large‑language‑model training and evaluation paradigms—supervised fine‑tuning (SFT), few‑shot in‑context learning (ICL), and KL‑regularized reinforcement learning (RLHF/RLVR). It shows that each method can be viewed as a two‑step process: first constructing a Bayes or Gibbs posterior over outputs or actions using a prior and a utility signal, then approximating this posterior via a forward‑KL projection onto a parametric family. The authors formalize ICL and SFT as amortized weight projections, and demonstrate that reward‑weighted SFT, reward‑weighted ICL, and advantage‑weighted SFT are all special cases of forward‑KL projection onto reward‑induced posteriors, while also outlining where these equivalences hold and where they break down.

By Junxin Fan
arXiv AI
Jun 9

How Transformers Reject Wrong Answers: Rotational Dynamics of Factual Constraint Processing

arXiv:2603. 13259v2 Announce Type: replace-cross Abstract: When a decoder-only transformer is forced to process matched correct and incorrect single-token continuations of a factual query, the two pathways through hidden-state space diverge in a specific way: displacement vectors from the query-only representation maintain approximately equal magnitude but rotate apart in direction.

By Javier Mar\'in