LLMRouter: An Open-Source Library for LLM Routing

Introduction

LLMRouter is an intelligent routing system designed to optimize LLM inference by dynamically selecting the most suitable model for each query. To achieve intelligent routing, it defines:

1. 🚀 Smart Routing: Automatically routes queries to the optimal LLM based on task complexity, cost, and performance requirements.
2. 📊 Multiple Router Models: Support for over 15 routing models, including KNN, SVM, MLP, Matrix Factorization, Elo Rating, Graph-based routers, BERT-based routers, Hybrid probabilistic routers, transformed-score routers, multi-round routers, and many additional advanced strategies.
3. 🛠️ Unified CLI: Complete command-line interface for training, inference, and interactive chat with Gradio-based UI.

Supported Routers

Single-Round Routers

Router	Training	Inference	Description
knnrouter	✅	✅	K-Nearest Neighbors based routing
svmrouter	✅	✅	Support Vector Machine based routing
mlprouter	✅	✅	Multi-Layer Perceptron based routing
mfrouter	✅	✅	Matrix Factorization based routing
elorouter	❌	✅	Elo Rating based routing
routerdc	✅	✅	Dual Contrastive learning based routing
automix	❌	✅	Automatic model mixing
hybrid_llm	✅	✅	Hybrid LLM routing strategy
graphrouter	✅	✅	Graph-based routing
causallm_router	✅	✅	Causal Language Model router
smallest_llm	❌	✅	Always routes to smallest model
largest_llm	❌	✅	Always routes to largest model

Multi-Round Routers

Router	Training	Inference	Description
router_r1	❌	✅	Pre-trained Router-R1 model for multi-turn conversations

Agentic Routers

Router	Training	Inference	Description
knnmultiroundrouter	✅	✅	KNN-based agentic router for complex tasks
llmmultiroundrouter	❌	✅	LLM-based agentic router for complex tasks

Get Started

Installation

Clone the repository and install from source using a virtual environment (e.g., with anaconda3):

# Clone the repository
git clone https://github.com/ulab-uiuc/LLMRouter.git
cd LLMRouter

# Create and activate virtual environment
conda create -n llmrouter python=3.10
conda activate llmrouter

# Install the package
pip install -e .

Note: PyPI package coming soon! Once published, you'll be able to install directly with pip install llmrouter.

Training a Router

Train various router models with your configuration:

# Train KNN router
llmrouter train --router knnrouter --config configs/model_config_train/knnrouter.yaml

# Train MLP router with GPU
llmrouter train --router mlprouter --config configs/model_config_train/mlprouter.yaml --device cuda

# Train MF router quietly
llmrouter train --router mfrouter --config configs/model_config_train/mfrouter.yaml --quiet

Running Inference

Perform inference with trained routers:

# Single query inference
llmrouter infer --router knnrouter --config config.yaml --query "What is machine learning?"

# Batch inference from file
llmrouter infer --router knnrouter --config config.yaml --input queries.txt --output results.json

# Route only (without calling LLM API)
llmrouter infer --router knnrouter --config config.yaml --query "Hello" --route-only

# Custom generation parameters
llmrouter infer --router knnrouter --config config.yaml --query "Explain AI" --temp 0.7 --max-tokens 2048 --verbose

Input file formats supported: .txt (one query per line), .json (list of strings or objects with "query" field), .jsonl (one JSON object per line).

Interactive Chat Interface

Launch a Gradio-based chat interface:

# Basic chat interface
llmrouter chat --router knnrouter --config config.yaml

# Custom host and port
llmrouter chat --router knnrouter --config config.yaml --host 0.0.0.0 --port 7860

# With public sharing link
llmrouter chat --router knnrouter --config config.yaml --share

# Specify query mode
llmrouter chat --router knnrouter --config config.yaml --mode full_context --top_k 5

Query Modes:

• current_only: Routes based on current query only (default)
• full_context: Combines all chat history with current query
• retrieval: Retrieves top-k similar historical queries for context

Direct Script Execution

You can also run the CLI scripts directly:

# Training
python -m llmrouter.cli.router_train --router knnrouter --config config.yaml

# Inference
python -m llmrouter.cli.router_inference --router knnrouter --config config.yaml --query "Hello"

# Chat
python -m llmrouter.cli.router_chat --router knnrouter --config config.yaml

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