Long Context Pre-Training with Lighthouse Attention
Lighthouse Attention addresses a fundamental scaling bottleneck in transformer training by replacing quadratic attention complexity with a hierarchical, gradient-free compression strategy that works during pre-training and can be discarded afterward. The technique symmetrically pools queries, keys, and values while maintaining causal masking, enabling models to train on extreme sequence lengths without the memory and compute penalties that currently limit context windows. This matters because sequence length remains a hard constraint on model capability, and training-time-only optimizations that vanish at inference sidestep the latency costs of other sparse attention schemes.
Modelwire context
ExplainerThe key detail the summary gestures at but doesn't unpack is the 'discard afterward' property: Lighthouse Attention is not a permanent architectural change but a scaffolding technique, meaning models trained with it are fully compatible with standard inference stacks without any runtime overhead or latency penalty.
This connects directly to the theoretical work covered in 'Characterizing the Expressivity of Local Attention in Transformers' from early May, which formalized why bounded-window attention sometimes outperforms global attention despite processing less context. Lighthouse Attention's hierarchical pooling operates in a similar design space, trading full pairwise token interaction for a structured approximation, but it does so only during training rather than as a permanent architectural constraint. That distinction matters: the expressivity tradeoffs the earlier paper identified apply to inference-time local attention, not to training scaffolds that are later removed. The KV cache compression work in 'Make Your LVLM KV Cache More Lightweight' addresses the same memory pressure from the inference side, making these two papers complementary approaches to the same resource ceiling hit at different points in the model lifecycle.
The credibility test here is whether models pre-trained with Lighthouse Attention on very long sequences (say, 128K tokens or beyond) match or exceed the downstream benchmark performance of models trained with standard attention on shorter sequences, at equivalent compute budgets. If published ablations show degradation on retrieval-heavy long-context evals like SCROLLS or HELMET, the compression is losing signal that matters.
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MentionsLighthouse Attention · scaled dot-product attention · transformers
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