# Katanemo releases Arch-Router 1.5B, a router that follows your own route descriptions

> For context: a Qwen2.5-1.5B-based model that maps a query to a user-defined route and returns JSON. Released under the Katanemo licence.

Published 2025-06-19

Canonical: https://shipped.anth.us/decisions/katanemo-arch-router-1-5b/

For context: Arch-Router is from mid-2025, outside the last twelve months, and is included as an early open router model. The card cites a paper, arXiv 2506.16655, published on 19 June 2025. The Hub repository was created on 30 May 2025.

Arch-Router is a compact 1.5B-parameter router that maps a query to a user-defined domain or action so that it can be sent to the best-suited model. It powers the Arch proxy server. It is built on Qwen2.5-1.5B. You define routes with a name and description, such as code generation or bug fixing, and pass them as JSON inside route tags along with the conversation. The model returns a JSON route name, or other if no route fits. Each route is tied to a preferred model.

The licence is the Katanemo licence, shown on the Hub with a research-use tag; the card links a LICENSE file. The Hub lists about 2B parameters in F16 where the text says 1.5B.

The card claims state-of-the-art results in matching queries with human preferences on conversational datasets, but gives no figures on the page.

A router that reads your route descriptions rather than guessing task difficulty. Read the licence before using it commercially.

## Sources
- https://huggingface.co/katanemo/Arch-Router-1.5B
- https://arxiv.org/abs/2506.16655

## Editor's first pass (AI-assisted)
- Real 4: Weights and GGUF builds are on the Hub under a Katanemo licence tagged for research use.
- Useful 3.5: Routes by user-written domain or action descriptions rather than fixed benchmarks.
- Notable 3: Powers the Arch proxy server.
- Novel 3.5: Preference-aligned routing is the angle in its paper.