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Long-context retrieval improved by spending the same attention budget on fewer, wider heads, and the gain survived freezing attention weights

AspireAI community · arXiv (Preferred Networks)
Holding the total attention budget fixed, the paper finds that allocating it to fewer, wider attention heads measurably improves long-context retrieval. On RULER-100, averaged over 13 tasks and seven context lengths from 4K to 256K, a 0.6B model scored 31.25 at head dimension 128 and 41.21 at head dimension 512, and a 3B model scored 35.93 versus 50.93. Pretraining loss and short-context non-retrieval performance were largely unaffected by head dimension, so the trade is specific to retrieval rather than general capability. Wider-head models also show a higher proportion of retrieval heads with comparable absolute retrieval-head counts, associating more parameters with retrieval. The ablations are the interesting part: the retrieval advantage persists even when the attention projection weights are frozen during long-context continual pretraining, which points at better adaptation of embeddings and MLPs rather than a quirk of attention updates. The limitation is that the models are small, at 0.6B and 3B, and each 3B allocation was run once.
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