The Take — The open-weights gap is real, and it is a price list

Three weeks ago I reported that Kimi K3.1 Pro had pulled within three points of Claude Opus 5.5, and the framing was that open weights had finally earned a scoreboard argument. The number was right. The conclusion was wrong, and it was wrong in the open-weights camp's favour.
The three-point gap was a measurement artifact. On the rewritten index, Kimi K3.1 Pro scores 46 against Opus 5.5's 58 — a 12-point gap, according to Artificial Analysis. Among models whose weights you can actually download today, DeepSeek V4.1 Flash 1017 and GLM-5.3 top out at 32, which is four points below Claude Haiku 5.5 at 36, never mind the leader. Our brief this afternoon laid out what changed inside the suite. What I want to argue is what the change proved.
The defence that no longer works
The standard open-weights response to a bad leaderboard is that the leaderboard is gamed: benchmarks are chosen to flatter whoever paid for them, and composite scores hide specialisation. That response was reasonable in general and wrong in this specific case, because the main thing v5 did was delete tests that everyone could study. Humanity's Last Exam gave way to a 1,000-question refined version. AA-Omniscience moved to a release that stripped saturated and leaked questions. CritPt's hard subset went private after the original turned out to be solvable. The mechanism that closed the gap in September was contamination, and the people who closed it were the models training on public questions.
You can see the suite is not built to favour one lab. Six different models lead six different evaluations: Kimi K3.1 Pro still tops Terminal-Bench 4.0 at 67%, Gemini 4 Argon tops AutomationBench at 78%, Sonnet 5.5 tops AA-Briefcase, Muse Wonder Full tops GDP.pdf. On the two evaluations that carry the most weight, Kimi scores 37% on HLE-Diamond against 68% for Opus 5.5, and 34% on Terminal-Bench-Science against 63% for Astra. Those are agentic and scientific tasks, and they are where open models are furthest behind — not because a benchmark committee decided so, but because that is the expensive part of training right now. It takes reinforcement-learning environments that resemble the eval, across several domains at once. Nathan Lambert makes the sharper version of this point: hill-climbing is easy, knowing what to hill-climb is hard, and the labs that can build the environments win the tasks that look like environments.
The fair objection
Here is where I have to be honest about what v5 costs, because the steelman is strong and it is not just cope.
A private test set is an unfalsifiable claim. When 60% of an index rests on questions nobody outside the evaluating organisation can read, the reader is trusting one team's judgment about what matters, one team's implementation of the harness, and one team's arithmetic — with no way to check any of it. The proof that this matters is in the same announcement: Artificial Analysis revised ambiguous and erroneous questions in AA-Omniscience, and the only reason anyone knows they were erroneous is that people could once see them. The same release reordered the top five in a direction that happens to favour OpenAI on coding and science, and moved GPT-6.1 Terra above Gemini 4 Argon and Fable 5.1, which is the kind of result that deserves a raised eyebrow rather than a citation. Effort settings swing a single model by 23 points, from 35 at low to 58 at max. A ranking that fragile is a ranking you can assemble to taste.
I take that seriously. I still do not think it rescues the three-point story.
Why the take holds
The claim under dispute was never "open weights are as good as closed models at everything." It was narrower and more interesting: open weights are within touching distance of the frontier, close enough that the price difference decides the purchase. That claim only ever held on tests the open models could train against. Strip those out and the distance is 12 points at the top and 26 points for downloadable weights — a different product category, not a rounding error.
And the price list, read properly, is the actual open-weights argument. Among the ten highest-scoring models, cost per task ranges from $0.96 for GPT-6.1 Terra to $13.04 for Claude Fable 5.1; Opus 5.5 costs $10.04 and Astra $6.24, while Sol sits four points off the lead at $1.27. A model at 32 that you can run on your own hardware, fine-tune, and keep when the vendor changes its terms is not competing with Opus 5.5. It is competing with Haiku, and on that comparison the gap looks survivable. What damaged the open-weights case was not the new ruler. It was the insistence on reading the old ruler's number as a frontier claim, which is how the 3-point story got written in the first place — by me, on a suite where the questions were public.
There is also a version test worth remembering. The same Astra that scored 61 in September, five points behind Anthropic, measures 57 under v5 while the leader measures 58 instead of 66. Quoting a score without its index version is now a factual error, and half the discourse this week is people arguing across versions without noticing.
What would change my mind
Kimi's weights are due by November 4. If they land near 46 and reproduce there when someone other than Artificial Analysis runs the suite, the gap is a fact about training infrastructure and my argument gets easier, not harder.
The thing that would actually unseat the take is different: a second independent evaluation, run by a different organisation, using a held-out public suite, that puts the best open model within five points of the leader. One such result and the 12-point gap becomes one org's opinion rather than a description of the field. The other path is process — publish the per-task answers on a lag, rotate the holdouts annually, show the disagreement between benchmarks instead of averaging it away. None of that is exotic. It is what a benchmark has to do before a procurement team is entitled to cite it.
Until then, the honest summary is uncomfortable for the side I would rather be on: open weights lost ground this month because the test got harder and the test got harder on purpose. That is not a conspiracy, and calling it one is how a movement spends its credibility on a leaderboard it cannot win and does not need.
Do you buy the 12-point gap, or do you think a private benchmark is just a press release with error bars? Write to us via our contact page.







