> I don't know which field you're talking about, but in general, math and cs journals do not have page limits.

A lot of physics journals do. Anything ending in "Letters" (e.g. Applied Physics Letters, Physical Review Letters".

Science has a word limit per article.

Nature doesn't have a hard limit, but if it exceeds 6-8 pages, it needs to be exceptional.

In CS, unlike in many other fields, the best work comes out as conference papers, not journals, and they do have strict page limits. Most arxiv papers I read become conference papers, not journal papers.

Have you ever tried publishing a paper to an IEEE Section 8 conference? The page limits are ruthless. TELFOR 2026 has a 4 - 8 pages maximum.

ACL conference papers usually cap the main body at 8 pages, with unlimited appendices. KDD has a hard limit of 9 pages plus 3 for references and appendices.

cryptography, for example, which is essentially math + cs together

Which journal?

look at essentially any proceedings of any conference (in crypto we dont really do journals). see EUROCRYPT for example https://link.springer.com/book/10.1007/978-3-031-91098-2 in there, every paper will be cut down and referring to full version for proofs etc. which are typically on eprint.iacr.org

Well, yes, conference proceedings are usually page limited, but that's not a journal.

In AI, conferences are far more prestigious than journals.

We usually do conferences in cryptography/security, and most of them have page limits: CCS, USENIX, NDSS, S&P, CRYPTO, EUROCRYPT all have page limits (some allow appendices, which reviewers are not obligated to read).