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Microsoft’s WINA Cuts LLM Inference Costs with Sparse Activation, No Training Required

DATE: 6/1/2025 · STATUS: LIVE

AI systems groan under inference demands until a radical sparse activation hack teases lightning-fast performance but conceals an unexpected twist…

Microsoft’s WINA Cuts LLM Inference Costs with Sparse Activation, No Training Required
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Large language models (LLMs) that incorporate billions of parameters form the backbone of many AI-enabled solutions in sectors such as finance, healthcare, and customer support. Their ability to generate text, summarize documents, and handle question-answering tasks has driven widespread adoption. Yet the computational burden of running inference through such extensive networks remains a major obstacle for organizations that seek to deploy these systems at scale. As each input requires a full forward pass, service providers face high latency and energy consumption costs.

The primary obstacle emerges during inference. Whenever an input, like a prompt or a document snippet, is fed into an LLM, every layer and every neuron activates in sequence, causing billions of parameter interactions. In reality, only a fraction of neurons contributes significant information to the final answer. Activating the entire parameter set leads to wasted computation. Researchers have developed sparse activation algorithms to address this inefficiency, turning off low-impact neurons at inference time. Most of these efforts, though, rely solely on measuring hidden state magnitudes and neglect how weight magnitudes shape error flow through the model.

Some existing sparse schemes leverage Mixture-of-Experts (MoE) frameworks, as seen in GPT-4 and Mistral, where a routing mechanism assigns input tokens to a small collection of expert sub-networks. That approach requires extensive extra training so the gating network can learn expert selection for each input. Alternative strategies like TEAL (Token-Efficient Activation Learning) and CATS (Channel-wise Activation Thresholding) trim computation by dropping neurons with lower activation values. These methods can misidentify critical neurons or retain nodes with little influence. They also demand careful threshold tuning for each model, which limits portability across different architectures.

To overcome these hurdles, teams from Microsoft, Renmin University of China, New York University and the South China University of Technology have unveiled WINA, short for Weight Informed Neuron Activation. WINA represents a training-free sparse activation method that considers both the activation strength of hidden units and the column-wise ℓ2 norms of weight matrices. By merging those two metrics, it consistently selects the most impactful neurons. WINA adapts automatically to each layer’s characteristics, eliminating the need for fine-tuning or manual threshold selection.

At the core of WINA is a simple computation: it multiplies each neuron’s hidden state value with its corresponding weight vector norm and then picks the top-K elements based on that product. This process constructs a smaller sub-network that retains the majority of signal-carrying pathways. Beyond this, WINA applies a lightweight tensor transformation that enforces column-wise orthogonality in the weight matrices—often implemented via a QR decomposition step. This orthogonal constraint guarantees that the theoretical bounds on approximation error remain valid in practice, keeping model predictions stable.

The research team tested WINA on a suite of popular LLMs—Qwen-2.5-7B, LLaMA-2-7B, LLaMA-3-8B and Phi-4-14B—across tasks such as reasoning, summarization and code generation, at sparsity rates from 30% up to 70%. In all experiments, WINA outmatched TEAL and CATS. On Qwen-2.5-7B with 65% inactive neurons, it delivered a 2.94% higher average accuracy than TEAL and a 1.41% gain over a TEAL variant with transformation. When applied to LLaMA-3-8B, WINA yielded a 1.06% improvement at 50% sparsity and 2.41% at 65%. On complex benchmarks like GSM8K arithmetic reasoning and the ARC Challenge, performance remained robust. Floating-point operations dropped by as much as 63.7% on LLaMA-2-7B and 62.7% on Phi-4-14B, translating into real-time speed-ups.

This approach provides a reliable, plug-and-play avenue for reducing inference costs in large language models without modifying original weights or adding training overhead. It can be deployed across varied architectures without extra configuration, making it an appealing option for settings that demand low latency, lower energy consumption and consistent output quality.

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