LightTransfer: Your Long-Context LLM is Secretly a Hybrid Model with Effortless Adaptation

Kavli Affiliate: Wei Gao

| First 5 Authors: Xuan Zhang, Fengzhuo Zhang, Cunxiao Du, Chao Du, Tianyu Pang

| Summary:

Scaling language models to handle longer contexts introduces substantial
memory challenges due to the growing cost of key-value (KV) caches. Motivated
by the efficiency gains of hybrid models and the broad availability of
pretrained large transformer backbones, we explore transitioning transformer
models into hybrid architectures for a more efficient generation. In this work,
we propose LightTransfer, a lightweight method that transforms models such as
LLaMA into hybrid variants. Our approach identifies lazy layers — those
focusing on recent or initial tokens — and replaces their full attention with
streaming attention. This transformation can be performed without any training
for long-context understanding tasks or with minimal fine-tuning for o1-like
long reasoning generation tasks that require stronger reasoning capabilities.
Experiments across diverse benchmarks and models (e.g., LLaMA, Mistral,
QwQ-STILL) demonstrate that, even when half of the layers are identified as
lazy, LightTransfer achieves up to 2.17$times$ throughput improvement with
minimal performance loss ($<1.5%$ on LongBench) and achieves 53.3% on math
benchmark AIME24 of advanced o1-like long reasoning model QwQ-STILL.

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