arXiv Computation and Language By Kirill Afendulev, Alexey Dontsov, Elena Tutubalina, Anton Korznikov

What Attention Recalls and Recurrence Controls in Hybrid Language Models

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Hybrid language models combine attention with a fixed-size recurrent state, yet the distinct roles of each component are not well understood. The authors introduce two cache-level interventions—split-prefill and state-swap—to isolate the contributions of the KV cache (attention) and the recurrent state. Experiments on Qwen3.5 and Falcon-H1 show that exact retrieval depends almost entirely on attention, while output language and persona rely mainly on recurrence, with the state-swap intervention confirming that answers derive from the KV side and language from the recurrent side.

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