SIGNALAI·Jun 24, 2026, 4:00 AMSignal75Medium term

LLMs are Bayesian, In Expectation, Not in Realization

Source: arXiv cs.LG

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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. We show this objection targets a structural invariant rather than the quantity scoring online prediction. For any Bayesian reference, excess prequential code length is exactly cumulative predictive KL. For unordered support sets that must be serialized, the expected regret of a single

Why this matters
Why now

Ongoing research into the theoretical underpinnings of large language models is actively refining our understanding of their capabilities and limitations.

Why it’s important

This paper clarifies a fundamental debate regarding the Bayesian nature of LLMs, impacting how we design, interpret, and trust these increasingly powerful AI systems.

What changes

Our theoretical understanding of LLM inference is evolving, differentiating between ideal Bayesian behavior and real-world transformer realization, which could guide future architectural improvements.

Winners
  • · AI researchers
  • · ML architects
  • · Bayesian learning practitioners
Losers
  • · Oversimplified interpretations of LLM learning
Second-order effects
Direct

It provides a more nuanced theoretical framework for understanding the internal workings of large language models.

Second

This improved understanding could lead to more robust and explainable AI models, potentially reducing unexpected behaviors.

Third

Long-term, a stronger theoretical foundation might accelerate progress toward true artificial general intelligence by clarifying learning mechanisms.

Editorial confidence: 90 / 100 · Structural impact: 60 / 100
Original report

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Read at arXiv cs.LG
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