Compose, don’t just choose.
Select a single model, escalate through a confidence cascade, deliberate with Fusion, or coordinate bounded micro-agent workflows.
Use the model path the request needs.
No model is best for everyone. vLLM Semantic Router selects, escalates, and coordinates models for each request—guided by user preference expressed through configurable signals and policy.
Your preference shapes the mixture
Models, compute, and locations keep diversifying. Preference defines what “best” means for each user and workload. Mixture-of-Models turns fragmented supply into preference-aligned intelligence.
Models, compute, and locations define what is available. Preference defines the right mixture.
Select a single model, escalate through a confidence cascade, deliberate with Fusion, or coordinate bounded micro-agent workflows.
Use the model path the request needs.
Route routine work to efficient model paths, reserve cascades and multi-model reasoning for requests that need them, and reuse similar answers with semantic caching.
Spend more only when more intelligence adds value.
Route across configured local, private, and cloud backends, keeping privacy-sensitive work on policy-approved paths and reaching cloud models when policy allows.
One routing policy across configured endpoints.
Encode priorities for quality, cost, latency, safety, privacy, modality, and hallucination tolerance as explicit signals and policies that shape each route.
The best mixture is the one aligned with the user.
16 signal families across heuristic and learned detectors, from knowledge base routing to history-aware reasks.
12 routing strategies spanning rules, latency heuristics, reinforcement learning, and ML selection.
18 research papers spanning routing, systems, safety, and multimodality.
The supported first-run path is a single installer that sets up the CLI and local serve flow on macOS and Linux.
curl -fsSL https://vllm-semantic-router.com/install.sh | bashResearch threads that trace the router's evolving ideas across safety, multimodality, orchestration, and system design.
vLLM Semantic Router Team
arXiv Technical Report
We introduce vLLM Semantic Router, a signal-driven decision routing framework for Mixture-of-Modality deployments that composes heterogeneous signals into deployment-specific routing policies across cost, privacy, latency, and safety constraints.
Huamin Chen, Xunzhuo Liu, Bowei He, Fuyuan Lyu, Yankai Chen, Xue Liu, Yuhan Liu, Junchen Jiang
arXiv Technical Report
We synthesize the project’s recent routing, fleet, multimodal, and governance results into the Workload-Router-Pool (WRP) architecture, connecting signal-driven routing to a full-stack inference optimization framework and outlining future research directions across workload, router, and pool design.
Xunzhuo Liu, Bowei He, Xue Liu, Andy Luo, Haichen Zhang, Huamin Chen
arXiv Technical Report
We formalize the visual confused deputy as a security failure mode in computer-using agents and introduce a dual-channel guardrail that independently checks click targets and action reasoning before execution.
Huamin Chen, Xunzhuo Liu, Junchen Jiang, Bowei He, Xue Liu
arXiv Technical Report
We introduce Outcome-Aware Tool Selection (OATS), an offline embedding refinement method that improves semantic-router tool ranking under single-digit millisecond CPU budgets without adding serving-time model inference.
Xunzhuo Liu, Bowei He, Xue Liu, Andy Luo, Haichen Zhang, Huamin Chen
arXiv Technical Report
We propose Adaptive VLM Routing (AVR), which estimates action difficulty and routes computer-use agent steps to the cheapest model that still satisfies a target reliability threshold.
Xunzhuo Liu, Bowei He, Xue Liu, Andy Luo, Haichen Zhang, Huamin Chen
arXiv Technical Report
We combine Flash Attention, prompt compression, and near-streaming body processing to cut routing latency from seconds to tens of milliseconds while keeping the router lightweight enough to share hardware with serving.
Huamin Chen, Xunzhuo Liu, Yuhan Liu, Junchen Jiang, Bowei He, Xue Liu
arXiv Technical Report
We present a queueing-theory-grounded fleet planner and discrete-event simulator for sizing multi-pool LLM GPU fleets against P99 TTFT targets, without requiring hardware profiling runs up front.
Huamin Chen, Xunzhuo Liu, Yuhan Liu, Junchen Jiang, Bowei He, Xue Liu
arXiv Technical Report
We derive the minimum-cost two-pool LLM fleet directly from the workload CDF and P99 TTFT target, then use Compress-and-Route to make the optimal boundary deployable in practice.
Huamin Chen, Xunzhuo Liu, Yuhan Liu, Junchen Jiang, Bowei He, Xue Liu
arXiv Technical Report
We derive the 1/W law showing that tokens per watt roughly halve whenever the serving context window doubles, making context-length routing topology a larger energy-efficiency lever than a pure GPU generation upgrade.
Xunzhuo Liu, Hao Wu, Huamin Chen, Bowei He, Xue Liu
arXiv Technical Report
We show how probabilistic ML predicates in policy languages can silently co-fire on the same query, and implement conflict detection plus a softmax-based prevention mechanism in the Semantic Router DSL.
Huamin Chen, Xunzhuo Liu, Bowei He, Xue Liu
arXiv Technical Report
We extend the Semantic Router DSL from stateless, per-request routing to multi-step agent workflows, emitting verified decision nodes for orchestration frameworks, Kubernetes artifacts, YANG/NETCONF payloads, and protocol-boundary gates from a single declarative source file.
Xunzhuo Liu, Bowei He, Xue Liu, Andy Luo, Haichen Zhang, Huamin Chen
arXiv Technical Report
We show that conversational memory and retrieval-grounded routing let a lightweight 8B model recover most of a 235B model’s performance on persistent user-specific queries while cutting effective inference cost by 96%.
Xunzhuo Liu, Bowei He, Xue Liu, Haichen Zhang, Huamin Chen
SIGIR 2026 Industry Track
We present a real-time verification component for long-document RAG that processes contexts up to 32K tokens, balancing latency and grounding coverage so interactive systems can detect unsupported answers without falling back to truncated checks.
Huamin Chen, Xunzhuo Liu, Junchen Jiang, Bowei He, Xue Liu
arXiv Technical Report
We propose token-budget-aware pool routing, which estimates each request’s total token budget using a self-calibrating bytes-per-token ratio and dispatches it to short or long vLLM pools to cut fleet cost while avoiding KV-cache failures.
Chen Wang, Xunzhuo Liu, Yuhan Liu, Yue Zhu, Xiangxi Mo, Junchen Jiang, Huamin Chen
NeurIPS - MLForSys
We present a semantic router that classifies queries based on their reasoning requirements and selectively applies reasoning only when beneficial.
Chen Wang, Xunzhuo Liu, Yue Zhu, Alaa Youssef, Priya Nagpurkar, Huamin Chen
We present a category-aware semantic caching where similarity thresholds, TTLs, and quotas vary by query category, with a hybrid architecture separating in-memory HNSW search from external document storage.
Huamin Chen, Luay Jalil
Internet Engineering Task Force (IETF)
This document specifies the Semantic Inference Routing Protocol (SIRP), a framework for content-level classification and semantic routing in AI inference systems.
H. Chen, L. Jalil, N. Cocker
Internet Engineering Task Force (IETF) - Network Management Research Group
This document specifies multi-provider extensions for agentic AI inference APIs. Published: 20 October 2025. Intended Status: Informational. Expires: 23 April 2026.
Routing Blueprint
An interactive walkthrough of signal extraction, projection coordination, decision logic, and model routing behavior.
Structural mapping from communication theory to the routing pipeline.
The user request is the raw source message before encoding.
Purpose-built encoders read intent, rank relevance, and classify modality before generation begins.
Sequence classification, token labeling, embeddings, and reranking collapse into one system-intelligence layer.
Detect and route text, image and audio inputs to the right modality-capable model.
Independently encode queries and candidates into dense vectors for similarity search and semantic caching.
Joint cross-attention scoring of query-candidate pairs for high-precision reranking.
Domain, jailbreak, PII and fact-check classification across 14 MMLU categories via ModernBERT with LoRA.
Bidirectional attention across tokens and sentences, with full context instead of causal masking.
Adjust embedding layers and dimensions at inference time to trade compute for accuracy on the fly.
Truncate embedding vectors to any dimension without retraining to balance accuracy and speed per request.
Innovation thrives when great minds come together
Steering CommitteeLLM Routing @ vLLM
Steering CommitteePostdoc @ MBZUAI / McGill
Steering CommitteePostdoctoral Associate @ McGill University / MBZUAI
Steering CommitteePhD Candidate @ McGill University / Mila
Steering Committee@Microsoft
Steering Committee@MBZUAI / McGill / Mila
CommitterCloud-native Open Source Contributor @Tongji University
CommitterGTM Tech Lead @Google
CommitterCloud-native Engineer @DaoCloud
CommitterComputer Science Engineer @Intuit
CommitterSoftware Engineer @DELTA ELECTRONICS, INC.
CommitterSDE, Data and AI @Red Hat
CommitterOpen Source Contributor
CommitterSenior Staff Research Scientist @IBM
CommitterStaff Research Scientist @IBM
CommitterR&D Manager @Red Hat
CommitterSenior Principal Engineer @Red Hat
CommitterAI Infrastructure / Cloud-Native PM @DaoCloud
Software Engineer @Red Hat
Senior Software Engineer @Red Hat
Software Engineer @Red Hat
Software Engineer @Red Hat
CommitterOpen Source Contributor @Red Hat
CommitterSoftware Engineer @Z.ai
CommitterSenior Software Engineer @Red Hat
CommitterSoftware Engineer @Red Hat
Software Engineer @Yokogawa
Open Source Engineer @DaoCloud
CommitterSenior Software Engineer @Kong
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
Steering CommitteeLLM Routing @ vLLM
Steering CommitteePostdoc @ MBZUAI / McGill
Steering CommitteePostdoctoral Associate @ McGill University / MBZUAI
Steering CommitteePhD Candidate @ McGill University / Mila
Steering Committee@Microsoft
Steering Committee@MBZUAI / McGill / Mila
CommitterCloud-native Open Source Contributor @Tongji University
CommitterGTM Tech Lead @Google
CommitterCloud-native Engineer @DaoCloud
CommitterComputer Science Engineer @Intuit
CommitterSoftware Engineer @DELTA ELECTRONICS, INC.
CommitterSDE, Data and AI @Red Hat
CommitterOpen Source Contributor
CommitterSenior Staff Research Scientist @IBM
CommitterStaff Research Scientist @IBM
CommitterR&D Manager @Red Hat
CommitterSenior Principal Engineer @Red Hat
CommitterAI Infrastructure / Cloud-Native PM @DaoCloud
Software Engineer @Red Hat
Senior Software Engineer @Red Hat
Software Engineer @Red Hat
Software Engineer @Red Hat
CommitterOpen Source Contributor @Red Hat
CommitterSoftware Engineer @Z.ai
CommitterSenior Software Engineer @Red Hat
CommitterSoftware Engineer @Red Hat
Software Engineer @Yokogawa
Open Source Engineer @DaoCloud
CommitterSenior Software Engineer @Kong
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
Steering CommitteeLLM Routing @ vLLM
Steering CommitteePostdoc @ MBZUAI / McGill
Steering CommitteePostdoctoral Associate @ McGill University / MBZUAI
Steering CommitteePhD Candidate @ McGill University / Mila
Steering Committee@Microsoft
Steering Committee@MBZUAI / McGill / Mila
CommitterCloud-native Open Source Contributor @Tongji University
CommitterGTM Tech Lead @Google
CommitterCloud-native Engineer @DaoCloud
CommitterComputer Science Engineer @Intuit
CommitterSoftware Engineer @DELTA ELECTRONICS, INC.
CommitterSDE, Data and AI @Red Hat
CommitterOpen Source Contributor
CommitterSenior Staff Research Scientist @IBM
CommitterStaff Research Scientist @IBM
CommitterR&D Manager @Red Hat
CommitterSenior Principal Engineer @Red Hat
CommitterAI Infrastructure / Cloud-Native PM @DaoCloud
Software Engineer @Red Hat
Senior Software Engineer @Red Hat
Software Engineer @Red Hat
Software Engineer @Red Hat
CommitterOpen Source Contributor @Red Hat
CommitterSoftware Engineer @Z.ai
CommitterSenior Software Engineer @Red Hat
CommitterSoftware Engineer @Red Hat
Software Engineer @Yokogawa
Open Source Engineer @DaoCloud
CommitterSenior Software Engineer @Kong
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
CommitterIndividual Contributor
vLLM Semantic Router is made possible by the open-source ecosystem.
Install, configure, train, and operate from one dense documentation graph.
Docs indexPapers, working groups, and contributors evolve the same system in public.
Community routes