Science1 publisher2 min readPublished
A twelve-year prime-gap record changed hands three times inside four days
Julia Stadlmann's cut to the small prime-gap bound was the first in twelve years, and a rumor pushed her to post it in August. Axiom Math and OpenAI both went lower before the preprint was four days old.
The Scientist · Science desk

What happened
- Julia Stadlmann of the University of Illinois Urbana-Champaign moved the record for the small prime-gap bound from 246 down to 240, the first advance on the problem in more than a decade.
- She heard rumors in mid-August that OpenAI was preparing a big announcement on prime gaps, and her postdoctoral mentor Kevin Ford told her to get the result onto the preprint archive at once.
- Within three days of her report on the last day of August, the AI startup Axiom Math had built on her approaches and beaten her number.
- Two hours after Axiom Math announced, OpenAI surpassed both records, and five days after that it claimed to have solved another major problem in mathematics.
- The previous bound of 246, reached by collaborative work in mid-2014 after Yitang Zhang's 2013 proof of a bound under 70 million, had stood for a dozen years.
Compiled by The ScientistSomething wrong?How this is made
Why it matters
- constraint The preprint archive was the only instrument fast enough to secure priority here. A result held back in August for refereeing would have become public only after two AI labs had passed it.
- decision Anyone within reach of a contested bound now chooses between months of improving a constant and posting a weaker number to keep the credit. Stadlmann chose to post.
- exposure Publishing a method exposes the headroom left in it. Axiom Math's improvement came out of Stadlmann's own approaches, three days after she made them readable.
- precedent Priority in this corner of number theory will be dated by preprint timestamps, because a journal cycle is longer than the interval in which the record changed hands three times.
A bound of 240 says that some gap of 240 or less between consecutive primes recurs infinitely often [2]. It does not say that a gap of two does. That is what the twin prime conjecture asserts, and it is still unproved [3][9]. Between the record and the conjecture sit 238 integers [23].
Each further cut in the bound costs more work. The year after Yitang Zhang's result cut the bound by a factor of roughly 280,000 [24]. The twelve years after that cut it by 6, a reduction of about 2.4 percent [22].
Those 6 came out of the weights. Sieve methods filter composite numbers partially rather than completely, weighting the filter so that multiples of 2 are removed more strongly than multiples of 3, and the partial filter describes the distribution of primes better than a complete one would [10]. Stadlmann found the optimal weights by piecing together regions of high-dimensional space where the competing approaches each prevail, then calculating the volumes of those regions with only a rough idea of what the regions look like [11]. Andrew Granville, a number theorist at the University of Montreal, said of it: "It goes beyond finding a needle in a haystack." [12] Kannan Soundararajan of Stanford called the problem "fiendishly difficult" and said, "It was really quite impressive." [13]
Her methods could have done better with more time, and she did not have it [15]. Kevin Ford, her postdoctoral mentor at Illinois, gave her the instruction in plain words: "Drop everything you're doing and put this result on the math preprint archive. Get it out there." [17] Counting from that posting to OpenAI's result, the whole sequence fits inside about 74 hours [25].
Ford also said, "It's a David-versus-Goliath story where the human gets the gold." [18] Terence Tao of UCLA, a Fields Medalist, wrote on mathstodon.xyz that "what we are seeing here is a consequence of some very deliberate choices to abandon any pretense of gaining human understanding ... and using AI tools for the sole purpose of achieving a benchmark" [19]. Science News reports that many researchers now see some AI companies as subverting professional norms and undermining the pursuit of knowledge [26].
Neither Axiom Math nor OpenAI has given the bound it reached, and OpenAI's later result on another famous problem stands as a claim [21][6]. Stadlmann's 240 arrived with a method other people can read and extend, and Axiom Math extended it in three days [11][4].
What to watch
- Whether Axiom Math and OpenAI publish the bounds they reached in a form other number theorists can check.
- Whether anyone pushes Stadlmann's weight-optimisation further, given the room left in it.
- Whether OpenAI's separate claim, five days later, to have solved another major mathematical problem holds up.