A router that decides where your money goes is asking for a lot of trust. It sits in front of every request, quietly picks a model, and sends you a bill at the end of the month. If it tells you it saved you 60%, you mostly have to take its word for it.
I didn't want to take its word for it. So OmnisRouter attaches a receipt to every response, and the receipt is the whole point.
It's an open source (Apache 2.0), self-hosted proxy that speaks the Anthropic, OpenAI and Gemini formats. You change one base URL, keep your own provider keys, and each request goes to the cheapest model that can actually handle it. The response comes back in your client's own format, with a note explaining what was chosen and what it cost.
The receipt
Every response carries a set of headers:
X-Omnis-Model: gemini/gemini-2.5-flash
X-Omnis-Decision: Routed
X-Omnis-Confidence: 0.26
X-Omnis-Policy: v3-omnisbench-2026-08-20
X-Omnis-Cost-Delta-Vs-Big: -0.0121
And if you want to know what it'd do before spending anything, there's a cost-free endpoint that returns the full decision without calling a provider:
curl -s localhost:8080/v1/route -H "authorization: bearer $TOKEN" \
-d '{"messages":[{"role":"user","content":"Summarize this thread."}]}'
{ "policy_version": "v3-omnisbench-2026-08-20",
"decision": "ROUTED", "reason": "cheapest_capable",
"chosen": { "provider": "gemini", "model_id": "gemini-2.5-flash" },
"est_cost_delta_vs_big_usd": -0.0121 }
No screenshot, no dashboard you have to trust. The decision's in the response, and you can log it.
How it actually decides
There's no network hop to work out where to send a request. A small pinned ONNX model (bge-small-en-v1.5) embeds the prompt in-process, the embedding maps to the nearest intent cluster, and the cluster's policy table picks the cheapest candidate that clears the quality bar for that kind of work. If it isn't confident, it escalates to a strong model rather than guessing. The whole thing happens in well under the 50ms I gave it as a budget.
Here's a live trace from the shipped model:
| Request | Routed to | Decision |
|---|---|---|
| Summarize this thread | gemini-2.5-flash | routed (cheap) |
| Prove sqrt(2) is irrational | gpt-5-nano | routed (cheap) |
| Write a Python function to merge two lists | gpt-5 | routed (strong) |
| Hello. | claude-opus-5 | escalated |
The maths row is the interesting one. On grade-school maths, the tiny gpt-5-nano is essentially as accurate as the frontier model, so OmnisRouter sends the work there and keeps the roughly 25x price difference. That's not a guess. It comes from measurement.
Where the numbers come from
The routing model isn't a black box I'm asking you to believe in. The intent clusters and the policy table ship in the repo and rebuild from public data, so the same inputs produce the same model, and every decision is stamped with the policy version that made it.
The coding and maths policy is driven by OmnisBench, a companion benchmark that grades each model per task and publishes every response so you can re-grade it offline. So when the router says "the cheap model is good enough here", that's a number you can go and check, not a line on a slide. Other domains use sensible estimates for now, and the benchmark coverage grows from there.
The honest bit
Cheapest-capable isn't the same as cheapest. The point isn't to slam everything into the smallest model and hope. It's to spend frontier money only where the work needs it, and to be able to show, per request, why it went where it went. When a capability can't be carried faithfully to the chosen provider, it refuses with an explicit error instead of silently dropping it. Surprising the first time, correct every time.
It runs as a single self-hosted process with an embedded database, your keys are encrypted at rest, and prompt content only ever leaves your infrastructure to go to the model you chose.
Have a look
- Site and the full routing story: https://omnisrouter.fortitude-omnis.group/
- Code: https://github.com/Fortitude-Group/OmnisRouter
- The benchmark behind the routing: https://omnisbench.fortitude-omnis.group/
If you can make it route something badly, or you think the receipt should carry more than it does, tell me. That's what the open model and the decision log are for.
OmnisRouter is built by Fortitude Omnis. We make small, sharp tools, and we try not to lie in our own marketing.
