The peak the server reports to Cfx.re itself, next to the one Argos measured.
It advertises 512 slots but currently holds 17 players — only 7% of its own peak of 251. Servers swing hard by hour of day; the chart below shows when it fills up.
This data comes from the public Cfx.re server directory and contains no player identities. If you run this server and want to screen your players against cheat history, Argos Guard does that at connect time.