A Hybrid Early-Exit Algorithm for Large Language Models Based on Space Alignment Decoding (SPADE)

Large language models are computationally expensive due to their deep structures. Prior research has shown that intermediate layers contain sufficient information to generate accurate answers, leading to the development of early-exit algorithms that reduce inference costs by terminating computation at earlier layers. However, these methods often suffer from poor performance due to misalignment between intermediate and output layer representations that lead to decoding inaccuracy. To address these challenges, we propose SPADE (SPace Alignment DEcoding), a novel decoding method that aligns intermediate layer representations with the output layer by propagating a minimally reduced sequence consisting of only the start token and the answer token. We further optimize the early-exit decision-making process by training a linear approximation of SPADE that computes entropy-based confidence metrics. Putting them together, we create a hybrid early-exit algorithm that monitors confidence levels and stops inference at intermediate layers while using SPADE to generate high-quality outputs. This approach significantly reduces inference costs without compromising accuracy, offering a scalable and efficient solution for deploying large language models in real-world applications.

Distributed Rule Vectors is A Key Mechanism in Large Language Models' In-Context Learning

Large Language Models (LLMs) have demonstrated remarkable abilities, one of the most important being In-Context Learning (ICL). With ICL, LLMs can derive the underlying rule from a few demonstrations and provide answers that comply with the rule. Previous work hypothesized that the network creates a "task vector" in specific positions during ICL. Patching the "task vector" allows LLMs to achieve zero-shot performance similar to few-shot learning. However, we discover that such "task vectors" do not exist in tasks where the rule has to be defined through multiple demonstrations. Instead, the rule information provided by each demonstration is first transmitted to its answer position and forms its own rule vector. Importantly, all the rule vectors contribute to the output in a distributed manner. We further show that the rule vectors encode a high-level abstraction of rules extracted from the demonstrations. These results are further validated in a series of tasks that rely on rules dependent on multiple demonstrations. Our study provides novel insights into the mechanism underlying ICL in LLMs, demonstrating how ICL may be achieved through an information aggregation mechanism.