Layer-Order Inversion: Rethinking Latent Multi-Hop Reasoning in Large Language Models

Code

• github.com/laquabe/layer-order-inversion
  OfficialIn paper★ 0

Abstract

Large language models (LLMs) perform well on multi-hop reasoning, yet how they internally compose multiple facts remains unclear. Recent work proposes hop-aligned circuit hypothesis, suggesting that bridge entities are computed sequentially across layers before later-hop answers. Through systematic analyses on real-world multi-hop queries, we show that this hop-aligned assumption does not generalize: later-hop answer entities can become decodable earlier than bridge entities, a phenomenon we call layer-order inversion, which strengthens with total hops. To explain this behavior, we propose a probabilistic recall-and-extract framework that models multi-hop reasoning as broad probabilistic recall in shallow MLP layers followed by selective extraction in deeper attention layers. This framework is empirically validated through systematic probing analyses, reinterpreting prior layer-wise decoding evidence, explaining chain-of-thought gains, and providing a mechanistic diagnosis of multi-hop failures despite correct single-hop knowledge. Code is available at https://github.com/laquabe/Layer-Order-Inversion.

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