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Posted by tdchaitanya 11 hours ago

Openrouter Fusion API(openrouter.ai)
176 points | 68 comments
all2 49 minutes ago|
I had a prompt I used for this just using Claude Code:

    Let's review <filepath or specific file> for architectural issues. Spawn 10 agents, create personas for them, have them review the _api.go and write their review to reviews/<persona>-review.md, then have each agent do a round robin response to 3 of the reviews of their choosing (based on the abstract at the beginning of each review) and write the response to response/<original file name>-<agent persona name>-response.md. Then we do rebuttals to the responses in rebuttals/<response file name>-rebuttal.md. Finally, each agent should launch agents to review the reviews, responses, and rebuttals to their review, and compile findings to findings/<original file name>-findings.md. Finally, have another agent compile the findings and write that to review-findings.md. Present a concise version of the findings here.
This works well with frontier models and even locally hosted models (last I used it was with Qwen 3.5).
dsl 7 hours ago||
Heh. I built "Fusion" a few months ago as an MCP using OpenRouter. The idea was to give Claude a "panel of experts" to go talk to when it got stuck.

After extensive testing and benchmarking I discovered that when you ask one model to judge another's response you don't actually get a better answer. You are just asking it "how closely does this resemble the answer you would have given me." Additional rounds and all the "obvious" solutions that pop into your mind reading the proceeding sentence are essentially just cranking up the temperature.

I did find a solution, but it is insanely expensive. Maybe if this gains traction I'll release mine.

ceroxylon 2 hours ago||
I made a rough version of this in 2024[0], interesting to see that the idea is still around. I had the ability to set "quality thresholds", but it didn't seem to matter, the frontier models pretty much always agreed with each other and scored the answer highly, I should revisit it since it is a whole different ballgame than it was 2 years ago.

[0] https://github.com/Ceroxylon/konsensis

fomoz 4 hours ago|||
I think it depends on whether the answer is verifiable.

I have tested two judge models in my apps:

1. Judge model for a resume tailor. It evaluated the result resume vs the base resume and JD and judged it out of 10 on fit and honesty. It worked well and was useful.

2. Review model in my LLM trading bot platform. It reviews decisions from the Main model. The problem here is that the bot is navigating ambiguity. So unless the Review model catches an outright blunder (e.g. making a decision on wrong candle price or a BUY when it should be a SELL), the Review model can do more harm than good.

First, it adds latency to decisions, decisions take twice the amount of time (like be 60s instead of 30s for Gemma 4 31B). Second, it can make the bot too cautious, because Review model only runs on BUY/SELL decisions and not HOLD decisions, so the bot will only make less trades instead of review model increasing number of trades (because of latency and cost).

So overall, I think you'll get better results with a better model single shotting it rather than a review model if the answer isn't easily verifiable. But then why do you need a judge model and not just have the same agent review itself?

ALSO, if you read the reasoning text for a reasoning model (like Gemma 4), you see that it ALREADY reviews itself. So it's doing its best, re-review isn't really adding information. It's an interesting experiment, but you need to evaluate on a case by case basis.

comboy 5 hours ago|||
Prompt matters. Obviously if you want another model opinion you must generate from the scratch using the same prompt and then you can try to synthesize, but working with an existing response can work if desired. I use explicit instructions to find issues with assigned severities and then these are going through the panel of judges, only issues passing certain threshold are fixed in the original response.

I'll share a revelation which vastly improved my results: tell judges to evaluate truth and usefulness/should-be-fixed axis separately. Because inevitably with a prompt that is forcing to find issues you will end up with nitpicks. Plus truth axis allows to better evaluate the issue-finder models for your use case.

That's some part of what happens when I generate explanations like this one: https://hanzirama.com/character/%E6%9D%A5#explain - at this point the site is a small side product of my LLMs-evaluation machinery.

Bonus content for patient readers: if you need top quality you will likely need to pin provider(s) on OR, :exacto is not enough to get good repeatable results especially for open-weights models.

zone411 1 hour ago|||
Yes, definitely not a new idea. I had a multi-turn composite model in 2024 that was outperforming the top models across benchmarks: https://x.com/LechMazur/status/1828804485033992514.
SubiculumCode 3 hours ago|||
I've found that if I tell a judge that the answer came from a small and weak local LLM, it will pick the answer apart brutally...but since I have not done this systematically, I dont know how well it generalizes past my vibes.

Anyone else fell like if you can trick the LLM into a mode where it "feels" superior, it will act the asshole very well?

fridder 3 hours ago||
Yeah. I usually do this by telling it to be adversarial and find gaps and holes. Not fool proof but it does seem to increase the quality. It has helped when using local models in particular.
SubiculumCode 2 hours ago||
Yeah, you have to shortcut the RL-trained people pleasing
bilater 2 hours ago|||
Nice - I built an npm package in a similar fashion called Agent Order: https://github.com/btahir/agent-order

I think there is alpha just have to be very careful how you let the models com up with solutions and collaborate.

WhitneyLand 5 hours ago|||
Yeah, same experience. It turned out that objectively better answers were not that easy to find plus the expense plus it’s slow.
awongh 3 hours ago|||
I've started to have different models review things like architectural planning docs- and I think for these more "fuzzy" outputs the differences between the outputs can be quite different and I can use my own "taste" to pick the best one.

I don't think it would work without a human in the loop but it is surprising to me how varied models' vibes are and how a system design varies by what it thinks is important to include and emphasize.

efromvt 4 hours ago|||
I’d be interested in the benchmarking if you ever write it up! People do seem to assume LLM as a judge/panel improves outcomes (and arguably it does in cases like code review?) but I suspect it is very situational and the priors from human panel of experts don’t always translate cleanly.
bushido 4 hours ago|||
I had a very similar experience. I'd be keen to see how you went about it if you release it.

Here's what I use: https://github.com/DheerG/swarms

sfilkin 4 hours ago|||
I've been thinking along those lines, too. Could you give a general overview of your solution?
dist-epoch 5 hours ago|||
I think it depends.

I regularly ask both GPT and Gemini to give me options - programming libraries to do X, architecture suggestions, names for projects/services/classes

After they answer I ask each model what does it think of the other answer, and to give me a final suggestion considering both answers.

Both GPT and Gemini would frequently say "that other answer is much better than my one, it considered X factor that I missed".

SubiculumCode 3 hours ago||
Try telling it the answer came from a small local LLM..the condescension can become palpable.
jiaosdjf 6 hours ago|||
But.. but I told the LLM that it is an _expert_, is that worth nothing??
CrazyStat 5 hours ago||
Make sure to remind it to make no mistakes.
ihaveajob 4 hours ago||
You found the smoking gun!
iosjunkie 4 hours ago||
prompting "no mistakes" was load-bearing
crooked-v 2 hours ago|||
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huflungdung 6 hours ago||
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cj 9 minutes ago||
Are there any good web apps for asking a single question to multiple LLMs? I frequently find myself switching between LLMs to compare results.

A unified UI would be great, although not obvious how useful the "fusion" value prop is.

monkeydust 24 minutes ago||
I have been experimenting with multi-agent llms for last month, as I put in the writeup for my repo and in the video the biggest value I have found is when you run a bunch of different agentic strategies in parallel then have a judge review the variance of them. So far that has uncovered interesting insights. The rest of it is so-so. Been fun but also expensive!

Repo with video: https://github.com/monkeydust/rightmind

michaelbuckbee 8 hours ago||
I ran a quick eval to see what this looks like qualitatively vs just calling Opus 4.7 or GPT 5.5 directly.

As expected, Fusion was 7x slower and 4x the cost.

This isn't a knock against it, just that it I think this places Fusion into a "use it only when you need it" category.

https://3fpi5avcqq.evvl.io/

nielsole 7 hours ago||
Sounds like fusion would be a really good distillation target?
IanCal 7 hours ago|||
Which models were you using under this? If you used the quality default as exists in the interface, it makes sense that it was ~4x the cost as it'd be 3 frontier models judged by one of those.

The idea would be to use fusion with simpler, cheaper models.

galsapir 7 hours ago|||
yeah its really counterintuitive i think; i.e, getting the right framework and structure for this to work probably isn't trivial, models really hate playing well together. i wonder how their version would fair in real world use.
jimmypk 5 hours ago||
[flagged]
alex7o 4 hours ago||
I have been thinking a lot about this and my simplified understanding is that each model can be seen as a bell curve over human knowledge and each model has a different distribution. Using multiple models would allow us to change the distribution of other models with text that is out of their original curve. But then if you think about it does SFP and RL even alter the original distribution of text enough that models have enough variety so that their combined output is something better or just an echo chamber I believe not but I have no way to prove it yet.
andai 8 hours ago||
Context:

Surpassing Frontier Performance with Fusion

https://news.ycombinator.com/item?id=48525392

And a slightly better UI here: https://openrouter.ai/fusion

On OpenRouter's fusion API your request is routed to several models simultaneously and a judge model combines their answers into a final response. This significantly boosts performance, at the cost of time (at least on the one benchmark they tested, a deep research benchmark).

They have a Budget preset consisting of 3 cheaper models (which roughly matches Fable on that benchmark, costing half as much), and a Quality preset of 3 expensive ones (which beats Fable, but costs twice as much as Fable).

Pareto graph: https://openrouter.ai/blog/images/blog/fusion-benchmark-cost...

Curiously, fusing a model with itself also boosted performance (2xOpus4.8 roughly matching Fable on the benchmark, but costing twice as much as Fable). There's a further, smaller gain from mixing different models. The main gain seems to be from additional test time compute.

Would love to see more research on this, especially focusing on the cheap models that came out recently (e.g. Fusing DSV4 with itself, or with Mimo), and to see what the tradeoffs look like between running a fusion (parallel test time compute) vs increased reasoning or turns.

wongarsu 7 hours ago||
> Curiously, fusing a model with itself also boosted performance

Back in the GPT2 to GPT3 era this was a pretty common thing to do. You are effectively taking more samples from the space of likely outputs. If your model can do the task 60% of the time just take 5-10 samples and implement some kind of majority voting

It became less common to use as models got high accuracy on problems where combining results is trivial. But with a more complex judge (a competent LLM) you can still get better results by just sampling more of the output space and picking out the best aspects

sigmoid10 8 hours ago|||
Interesting how well a panel of Fable 5 + GPT 5.5 beats the frontier of either one, but if you add Gemini into the mix the panel of three performs worse, not better. To me that sounds like Gemini is worse at the given tasks but better at convincing judges of its solutions. Oh and a Panel of 2 Opus 4.8 models is almost exactly as good as one Fable 5. That smells suspicious. Do we know if that might simply be what Anthropic is doing behind the curtain?
qsort 8 hours ago|||
Yeah, GPT 5.5 + Fable beating either individually is belivable, but 2x Opus > Fable is what makes me a bit dubious about the whole thing. They might be measuring skills that are too specific or benefit a lot from more tokens being thrown at them. Also Claude Code (the harness) is not the best at the moment, that might be part of it as well?
andai 4 hours ago||
What throws me off is DeepSeek beating both Opus 4.8 and GPT 5.5.

That definitely doesn't sound right.

andai 4 hours ago||||
> Interesting how well a panel of Fable 5 + GPT 5.5 beats the frontier of either one, but if you add Gemini into the mix the panel of three performs worse

I'm not seeing that? Did you maybe misread the #2 ranked one as Fable + GPT + Gemini? It's actually Opus + GPT + Gemini.

waysa 8 hours ago|||
> Oh and a Panel of 2 Opus 4.8 models is almost exactly as good as one Fable 5. That smells suspicious. Do we know if that might simply be what Anthropic is doing behind the curtain?

I wouldn't be surprised if Fable/Mythos is a model distilled from a Panel/Council of Claude instances. Recursive self improvement is something all AI labs must be working on in some way or another.

jorvi 8 hours ago||
I don't know if it is still the case with current models, but a few generations back Microsoft had some research results where asking a model to iterate N times would significantly improve performance, with the optimal point being 4 iterations.
andai 4 hours ago|||
I think there's a sweet spot for it. If a model can't do a task, iterating won't help. If a model can do it reliably, there's no need to iterate.

If it can do it, but unreliably, that's where you would get major gains from iterating. I think the Chinese models are in that sweet spot, for many tasks. I would love to test that.

I started working on my own fusion system yesterday. I'm not sure how to benchmark it though.

The thing I'm most interested in is reliability. Going from 90% to 95% on a benchmark doesn't seem like much but you've cut the error rate in half.

Garlef 8 hours ago|||
> but a few generations back

Out of interest: Was this still before CoT/thinking-mode became the norm?

arizen 7 hours ago||
Some anecdata on Fusion: I run same query I used for Fable on OR Fusion and results were worse.

It felt, like Fable was able to kinda grasp very deep knowledge/intelligence layers and outline solution not only in agreeable way, but rather it proposed to prioritize solution items, with discarding some of the items, which made a lot of sense to me.

While Fusion felt more like a bit diversified answer of the same class of pre-Fable SOTA models, without touching the depth of knowledge/intelligence layers, which Fable was able to get, in my very limited tests I did, while Fable was accessible.

SteveMorin 5 hours ago||
Spent the weekend inspired by the new openrouter fusion model and wanted to see if it could run in Claude Code and if I could make it very easy for everyone else to try.

Built - claude-fusion-launcher — run Claude Code on a panel of models, not just one

Also shows cost

https://github.com/smorinlabs/claude-fusion-launcher

admn2 3 hours ago|
Doesn't it get expensive fast? I found the one-off prompts I did in their website to cost almost a $1/prompt.
SteveMorin 3 minutes ago||
Yes does get expensive fast
ElFitz 3 hours ago|
I’ve been experimenting with two things on this:

- multi-model consensus, with multiple cross-review rounds. Obviously, the number of inference tasks explodes with the number of models. Led to some interesting results [^0].

- giving an agent "stray thoughts" produced by the same model, or another, giving the second model a selection of the agent’s context, with different triggers (random, loop detection,…)[^1]. So far has proven very helpful and much cheaper than the first.

[0]: https://github.com/lightless-labs/refinery

[1]: https://github.com/Lightless-Labs/skunkworks/tree/main/flux

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