# vLLM Semantic Router introduces System Duo for fast and deep reasoning routing

> Original title: One router, two minds 🧠⚡

- Source: vLLM
- Published: 2026-11-05T23:21:07.000Z
- Bad Influence: https://badinfluence.news/items/evetig9qzk23byo08m6ygvfao
- Original: https://x.com/vllm_project/status/2118483782223470605

## Summary

vLLM Semantic Router introduces System Duo, which uses fast decision models for quick calls such as triage, guard, verify, and check. The router sends deep reasoning tasks to the right model only when needed. The system is open source and runs on vLLM.

## Post

One router, two minds 🧠⚡

 Huge work from @XunzhuoLiu and the vLLM Semantic Router team on System Duo — fast decision models handle the blink-of-an-eye calls (triage, guard, verify, check), while the router sends deep reasoning to the right model only when it matters.

 All open source, all running on vLLM → http://app.vllm-sr.ai

## Quoted post @XunzhuoLiu

> 𝗠𝗮𝗸𝗲 𝘆𝗼𝘂𝗿 𝗮𝗴𝗲𝗻𝘁 𝘁𝗵𝗶𝗻𝗸 𝗳𝗮𝘀𝘁 𝗮𝗻𝗱 𝘀𝗹𝗼𝘄.
> 
> System One decides in a blink. System Two reasons in depth.
> 
> 𝗢𝗻𝗲 𝗿𝗼𝘂𝘁𝗲𝗿. 𝗧𝘄𝗼 𝗺𝗶𝗻𝗱𝘀.
> 
> 𝗜𝗻𝘁𝗿𝗼𝗱𝘂𝗰𝗶𝗻𝗴 𝗦𝘆𝘀𝘁𝗲𝗺 𝗗𝘂𝗼 → https://app.vllm-sr.ai
> 
> #Jev #SystemOne #SystemTwo #OpenSource

https://x.com/XunzhuoLiu/status/2118445187051733452