Arena AI Model ELO History
59 points by mayerwin 7 hours ago | 42 comments
Hi HN,

I built a live tracker to visualize the lifecycle and performance changes of flagship AI models.

We've all experienced the phenomenon where a flagship model feels amazing at launch, but weeks later, it suddenly feels a bit off. I wanted to see if this was just a feeling or a measurable reality, so I built a dashboard to track historical ELO ratings from Arena AI.

Instead of a massive spaghetti chart of every single model variant, the logic plots exactly ONE continuous curve per major AI lab. It dynamically tracks their highest-rated flagship model over time, which makes both the sudden generational jumps and the slow performance decays much easier to see. It took quite a lot of iterations to get the chart to look nice on mobile as well. Optional dark mode included.

However, I have a specific data blindspot that I'm hoping this community might have insights on.

Arena AI largely relies on testing API endpoints. But as we know, consumer chat UIs often layer on heavy system prompts, safety wrappers, or silently switch to heavily quantized models under high load to save compute. API benchmarks don't fully capture this "nerfing" that everyday web users experience.

Does anyone know of any historical ELO or evaluation datasets that specifically scrape or test outputs from the consumer web UIs rather than raw APIs?

I'd love to integrate that data for a more accurate picture of the consumer experience. The project is open-source (repo link in the footer), so I'd appreciate any feedback, or pointers to datasets!


underyx 5 hours ago
> the slow performance decays

the decays are just more capable other models entering the population, making all prior models lose more frequently

reply
TekMol 2 hours ago
No, that is not how ELO scores work.
reply
qnleigh 2 hours ago
As far as I understand, this is exactly how ELO scores work. If a more capable show up and starts beating all the other models, it literally takes ELO points from everyone else.

https://en.wikipedia.org/wiki/Elo_rating_system

reply
harperlee 41 minutes ago
Depends on the test design; is an agent competing against other agent in a given match, or against a test? Plus! Does the test's ELO fluctuate?
reply
whiplash451 2 hours ago
It depends what you use as an anchor. If the anchor is a fixed model, you’re right. If the anchor is updated to a better model over time, then the elo of historical models degrades, right?
reply
tedsanders 5 hours ago
For what it's worth, I work at OpenAI and I can guarantee you that we don't switch to heavily quantized models or otherwise nerf them when we're under high load. It's true that the product experience can change over time - we're frequently tweaking ChatGPT & Codex with the intention of making them better - but we don't pull any nefarious time-of-day shenanigans or similar. You should get what you pay for.
reply
selcuka 5 hours ago
> we don't switch to heavily quantized models

That sounded like a press bulletin, so just to let you clarify yourself: Does that mean you may switch to lightly quantized models?

reply
jychang 4 hours ago
There's almost 0% chance that OpenAI doesn't quantize the model right off the bat.

I am willing to bet large amounts of money that OpenAI would never release a model served as fully BF16 in the year of our lord 2026. That would be insane operationally. They're almost certainly doing QAT to FP4 for FFN, and a similar or slightly larger quant for attention tensors.

reply
selcuka 4 hours ago
It's ok if they never release a BF16 model, but it's less ok if they release it, win the benchmarks, then quantise it after a few weeks.
reply
Ciph 5 hours ago
Thank you for your answer. I have a similar question as OP, but in regards of the GPT models in MS copilot. My experience is that the response quality is much better when calling the API directly or through the webUI.

I know this might be a question that's impossible for you to answer, but if you can shed any light to this matter, I'd be grateful as I am doing an analysis over what AI solutions that can be suitable for my organisation.

reply
sans_souse 2 hours ago
As phrased the only answer is the question; "as opposed to what?"
reply
aiscoming 2 hours ago
webUIs have giant system prompts built in

APIs have much smaller ones

reply
_kidlike 2 hours ago
its very interesting to see that this only happens to American companies. What gives?
reply
ponyous 2 hours ago
Seems like Chinese labs are the only ones that are trustworthy (at least when it gets to this specific issue). This feels so ironic haha
reply
mordae 2 hours ago
I am using novita-hosted DeepSeek V4 (Flash) for work and DeepSeek API for personal projects.

Novita's has occassional problem counting white space. DeepSeek hosted does not.

No idea why.

reply
whiplash451 2 hours ago
Neat. Would you add the option to normalize the elo over time (e.g update the model used as an anchor for the elo computation) so the diff between labs is more visible?
reply
eis 5 hours ago
The Elo rating system measures relative performance to the other models. As the other models improve or rather newer better models enter the list, the Elo score of a given existing model will tend to decrease even though there might be no changes whatsoever to the model or its system prompt.

You can't use Elo scores to measure decay of a models performance in absolute terms. For that you need a fixed harness running over a fixed set of tests.

reply
TurdF3rguson 46 minutes ago
Is that strictly true? ELO rankings do also inflate over time (looking at you, Chess GMs)
reply
bob1029 2 hours ago
The relative and auto-scaling nature of Elo ranking feels like an advantage here.

Relative ranking systems extract more information per tournament. You will get something approximating the actual latent skill level with enough of them.

reply
eis 2 hours ago
Advantage for what exactly though? I'm not saying Elo Ranking doesn't give any information. It just doesn't give the information that the OP's project claims to be able to give: that models get nerfed over time. You could extract this kind of information from the raw results of each evaluation round between two models, ignoring any new model entries and compare these over time but not from the resulting Elo scores with an ever changing list of models.

New models are on average better than older models, the average skill of the population of models increases over time and so you are mathematically guaranteed that any existing model will over time degrade in Elo score even though it didn't change itself in any way.

It's like benchmarking a model against a list of challenges that over time are made more and more difficult and then claiming the model got nerfed because its score declined.

Elo is good at establishing an overall ranking order across models but that's not what this is about.

To detect nerfing of a model, projects like https://marginlab.ai/trackers/claude-code/ are much much better (I'm not affiliated in any way).

reply
cherioo 4 hours ago
The interesting thing I find is how Anthropic has been more consistently improving over time in the last few years, that allows it to catchup and surpass OpenAI and Google. The latter two have pretty much plateau over the last year or so. GPT 5.5 is somehow not moving the needle at all.

I hope to see the other labs can bring back competition soon!

reply
XCSme 3 hours ago
Gpt 5.5 is quite a big leap, it's a lot better than opus 4.7 for agentic coding
reply
energy123 3 hours ago
Arena only allows very small context sizes, so it's a noisy benchmark for what we care about IRL.
reply
mettamage 2 hours ago
Better in what ways? I'm just curious about your experience.
reply
XCSme 2 hours ago
Consistency, not making mistakes.
reply
mettamage 2 hours ago
Ahh... that is indeed an issue I have with Claude. I'll check it out!
reply
fph 2 hours ago
Very neat! It would be great to extend it to non-flagship models as well.
reply
kimjune01 3 hours ago
Although Arena is adversarial and resistant to goodharting, it's not immune. Models that train on Arena converge on helpfulness, not necessarily truthiness
reply
jdw64 3 hours ago
This is great, but personally, I really wish we had an Elo leaderboard specifically for the quality of coding agents.

Honestly, in my opinion, GPT-5.5 Codex doesn't just crush Claude Code 4.7 opus —it's writing code at a level so advanced that I sometimes struggle to even fully comprehend it. Even when navigating fairly massive codebases spanning four different languages and regions (US, China, Korea, and Japan), Codex's performance is simply overwhelming.

How would we even go about properly measuring and benchmarking the Elo for autonomous agents like this?

reply
vachanmn123 3 hours ago
Isn't code that you fail to understand literally a sign that its worse?
reply
jdw64 3 hours ago
It was often much faster, and when I revisited the code later, there were cases where I realized it had moved the implementation toward a better abstraction.
reply
jdw64 3 hours ago
I should also add that I am not claiming to be a particularly great programmer. I have never worked at FAANG, and I haven't had much exposure to the kind of massive codebases those engineers deal with every day.

Most of the code I've worked with comes from Korean and Chinese startups, industrial contractors, or older corporate research-lab environments. So I know my frame of reference is limited.

When I write code, I usually rely on fairly conservative patterns: Result-style error handling instead of throwing exceptions through business logic, aggressive use of guard clauses, small policy/strategy objects, and adapters at I/O boundaries. I also prefer placing a normalization layer before analysis and building pure transformation pipelines wherever possible.

So when Codex produced a design that decoupled the messy input adapter from the stable normalized data, and then separated that from the analyzer, it wasn't just 'fancier code.' It aligned perfectly with the architectural direction I already value, but it pushed the boundaries of that design further than I would have initially done myself.

This is exactly why I hesitate to dismiss code as 'bad' just because I don't immediately understand it. Sometimes, it really is just bad code. But sometimes, the abstraction is simply a bit ahead of my current local mental model, and I only grasp its true value after a second or third requirement is introduced.

To be completely honest, using AI has caused a significant drop in my programming confidence. Since AI is ultimately trained on codebases written by top-tier programmers, its output essentially represents the average of those top developers—or perhaps slightly below their absolute peak.

I often find myself realizing that the code I write by hand simply cannot beat it

reply
tedsanders 5 hours ago
FYI, Elo isn't an acronym - it's a person's name. No need to capitalize it as ELO.
reply
alex_duf 2 hours ago
Electric Light Orchestra anyone?
reply
andrewshadura 3 hours ago
Unless you've just missed your last train to London.
reply
SilverElfin 5 hours ago
reply
gitowiec 4 hours ago
> ELO ratings

Thank you, I just looked at the chart and said to myself: ELO? YOLO!

That Elo ranking is also called chess ranking

reply
andrewshadura 3 hours ago
Élő. Meaning alive (él = it lives, -ő = adjective)
reply
Thomashuet 4 hours ago
It seems to be a USA only thing, Chinese models and Mistral don't show any downward trend.
reply
patall 3 hours ago
Wouldn't it be really weird if a open-weight model dropped in performance? Because then, it would rather be the Elo ranking
reply
refulgentis 4 hours ago
Is this slop? It has wildly aggressive language that agrees with a subset of pop sentiment, re: models being “nerfed”. It promises to reveal this nerfing. Then, it goes on to…provide an innocuous mapping of LM Arena scores that always go up?
reply
ninjalanternshk 41 minutes ago
It links to the GitHub repo for the project, and while it’s not inconceivable that an AI bot would create and populate a functioning public GitHub repo, it’s pretty unlikely.
reply
gptbased 2 hours ago
[dead]
reply