arXiv Machine Learning

Embedding Geometry Shapes LLM Routing: Tracing Failure Modes and Improving Generalization

arXiv Machine Learning
Aug 13

LLM Router: Rethinking Routing with Prefill Activations

arXiv:2603. 20895v3 Announce Type: replace-cross Abstract: Existing routers rely on semantic query features or handcrafted features, which often fail to capture model-specific failures or intrinsic task difficulty.

By Tanay Varshney, Annie Surla, Michelle Xu, Gomathy Venkata Krishnan, Maximilian Jeblick, David Austin, Neal Vaidya, Davide Onofrio
arXiv AI
Oct 9

RouterInterp: Understanding Superposed Specialisation in Mixture of Experts Routing

RouterInterp: Understanding Superposed Specialisation in Mixture of Experts Routing proposes the Superposed Specialisation Hypothesis (SSH), suggesting that experts in Sparse Mixture of Experts models specialise in a disjoint union of fine‑grained features rather than a single domain. The paper introduces RouterInterp, a method that identifies Sparse Autoencoder features predictive of routing decisions and generates unified natural‑language explanations. On the gpt‑oss‑20b model, RouterInterp achieves approximately 65% higher detection accuracy than previous token‑statistics based methods, offering a scalable way to explain expert routing.

By Ilya Lasy, Nora Yinuo Cai, Kola Ayonrinde
arXiv Computer Vision
Sep 18

Not All Layers Are Equal: Dynamic Layer Routing for Reliable CLIP OOD Detection

The paper introduces Voyager, a lightweight router that learns to select a sparse, final‑layer‑anchored expert from CLIP’s layer depth for out‑of‑distribution (OOD) detection. Using a weak OOD supervision context, Voyager outperforms state‑of‑the‑art prompt‑learning methods on three benchmarks, achieving an average FPR@95 of 18.86 on ImageNet‑1K. The router can be trained in about two minutes with less than 1 GB of memory, making it roughly 20× more efficient than existing approaches.

By Ignacio M. De la Jara, Cristian Rodriguez-Opazo, Damith Ranasinghe
arXiv AI
Sep 3

SCX Router: Streaming Zero-Shot Model Selection with a Decoder-KV Classifier and a Real-World Task Ontology

The paper introduces SCX Router, a lightweight GLiClass-based model selector that assigns suitability scores to inference-time language models without autoregressive generation. It uses a 0.6B-parameter Qwen3 decoder with a shallow bidirectional scorer, preserving a text-only key–value cache across sessions and predicting task attributes such as type, difficulty, and expected output length. The authors build a comprehensive task ontology with 23 families, 115 types, and 1,173 synthetic examples, generating 150,000 verifier-scored tasks to train the router, which outperforms baseline models on LiveBench subsets with a top‑1 score of 0.707 versus 0.696 for the strongest fixed model.

By Ihor Stepanov, Aleksandr Smechov, Mykhailo Shtopko, Dmytro Vodianytskyi, Oleksandr Lukashov