The max level for Icy Arsenal in Last Z: Survival Shooter is Level 50. A public upgrade reference for the game’s S3 tiles states that the combat buildings, including Icy Arsenal and Icy Fort, cap at L50.

Quick note

Another season guide says the same general season-3 installations can be scaled only to Level 30 in that context, which appears to refer to a different season/building category rather than Icy Arsenal’s combat-building cap. For the specific question about Icy Arsenal , the clearest answer is 50.

Source context

  • Combat buildings: Icy Arsenal, Icy Fort → max 50.
  • Season 3 installations in one guide → max 30.

TL;DR: Icy Arsenal’s max level is 50.