Upcoming Changes (Ratings, Ranks, and Moderators) (3 July 2026)

[euler]

The departure of the fastest solvers tables due to the data becoming increasingly polluted with cheats and members using genAI has meant more than just their removal from public view. It has also meant that one of the primary metrics we have used to rate problem difficulties has become increasingly unreliable. In an attempt to find a long term solution to this we have investigated other candidates, and we believe that we have found a balanced hybrid system that should provide measures that are less volatile and in theory can be used with confidence for many years.

Consequently, Project Euler will be taken offline briefly on Saturday to update the site with the new rating system. As mentioned, the previous metric relied heavily on the fastest solvers data, but with extensive correlation analysis it became clear that the fastest solvers data had a definite bias for certain types of problems. Fortunately, all of the new metrics we will be using: dynamic rating, demographic solves, and team ratings, generally agree with each other, which grants a greater degree of confidence in their combined reliability. However, we ask you to prepare for some surprising and, in some cases, seismic shifts in either direction. You will see some previously hard rated problems move down and at the same time other problems will shoot up towards the top.

We appreciate that this might be frustrating for those of you who had been working on that elusive problem at a particular difficulty level. So, ideally we do not want to make any significant changes after this, but there does remain scope to make small calibrations if necessary.

In addition to this, we have also decided to change the number of members at each rank to allow more to feel included. Moving from squares to cubes, we will have 100 Spheres, 800 Icosahedrons, 2700 Dodecahedrons, 6400 Octahedrons, 12500 Cubes, and 21600 Tetrahedrons, which means that 44100 members in total would have a ranked status.

After this update you will also notice below each problem that the information for each problem contains a lot more data. It will show a mean completion time of the most skilled solvers along with some fascinating demographic data, showing the percentage of members at each rank who have successfully solved the problem.

We would also like to thank Icy, griff, and Pacôme for joining a new moderator team. They are well known and respected members in the Project Euler Discord community. Their roles will include helping to keep the discussion threads up to the same high standards we have come to expect, including the removal of posts that disregard our genAI policy. They will also have the capability of viewing profiles of members flagged with suspicious solve patterns and taking action where necessary to help protect the integrity of the vast majority of our members, whilst ensuring that "cheats rarely prosper".

Finally, once we have completed this update and dealt with any bugs, we will be earnestly moving into the next major phase. We can't go into too much detail at this stage, but currently we are planning to introduce private and custom "groups" to Project Euler which will allow like-minded members to track each others progress. We are very excited by this and we hope you share our enthusiasm.

[TitanCode]

Looking at https://projecteuler.net/minimal=problems
I see:
994##Counting Triangles##2026-04-26 01:00:00##124######60

Rank and Level is missing?

[euler]

That was a leftover from my final testing that I forgot to change back. It should be working again now.

[JakubStawarczyk]

Wow, quite a massive change!
Almost all my harder problems are now classified as easier (rightly so)
But IMO good direction -> looking into fastest solvers (like 1min30s) gave the impression that something is not correct.

[euler]

Out of interest, which problem were you referring to with a fastest solve time of 1 minute 30 seconds?

[JakubStawarczyk]

This one was a shocker:
https://projecteuler.net/problem=978

But the winner is a Sphere, so probably just a "known" problem for pro solvers.

[TitanCode]

Plotting problem ID vs level change I see levels around ID 200 generally being lowered and levels from ID 500 and forward generally going up. This was also my gut feeling about difficulty.

Here are the biggest changes compared to data from June 15th:

Id title old level, new level, diff
186 Connectedness of a Network 19 7 -12
194 Coloured Configurations 31 19 -12
195 $60$-degree Triangle Inscribed Circles 28 15 -13
247 Squares Under a Hyperbola 25 13 -12
259 Reachable Numbers 25 12 -13
260 Stone Game 26 14 -12
274 Divisibility Multipliers 22 7 -15
413 One-child Numbers 29 16 -13
693 Finite Sequence Generator 19 33 14
712 Exponent Difference 12 25 13
722 Slowly Converging Series 14 26 12
744 What? Where? When? 19 31 12
756 Approximating a Sum 15 30 15
817 Digits in Squares 11 24 13
835 Supernatural Triangles 13 27 14
838 Not Coprime 12 24 12
848 Guessing with Sets 22 34 12
871 Drifting Subsets 13 28 15
874 Maximal Prime Score 13 27 14
894 Spiral of Circles 17 29 12
897 Maximal $n$-gon in a region 14 26 12
898 Claire Voyant 17 29 12
901 Well Drilling 18 31 13
945 XOR-Equation C 19 31 12
952 Order Modulo Factorial 16 31 15
953 Factorisation Nim 24 36 12
979 Heptagon Hopping 18 30 12
981 The Quaternion Group II 16 28 12

I mostly agree for the those I have solved, except this one:
991 Fruit Salad 20 29 9
Increased from lv 20 to 29. I think 20 was already too high

[euler]

It's good to hear that the new levels better align with your experience. Keep in mind that the data can't lie. We have not intervened or curated those difficulties. They are based on real encounters and who has been solving them. Problem 991 is bit of a phenomena. It is certainly not an easy problem, but it resembles another problem. So a lot of people have tried it based on that and failed. Rather than persist, it seems they give up, allowing the problem to earn an unbalanced number of undeserved wins.

[JakubStawarczyk]

Stats by location are disabled. Are they coming back or removed?