This one [0] about the Higgs boson is hard to beat. Pages 25-32 are just full of around 5150 „authors“, pages 33-37 are their affilliations.
Even without that particularly special case, high-energy physics collaborations have long since broken the idea of authors. There are now many collaborations with hundreds of authors publishing regularly and quite a few that are into the thousands.
I think the number is ~2930 authors according to the CDS [1] which is comparable to the corresponding CMS paper which has about ~2900 authors [2]
[1] https://cds.cern.ch/record/1471031
[2] https://impact.ornl.gov/en/publications/observation-of-a-new...