Have you profiled your game? (https://docs.unrealengine.com/latest…e/Performance/) this will help you see where the CPU is spending it’s time.
Having 100 characters all animating at full LOD, and using BTs/Perception/etc can strain the PC. If they are not on screen, there are tricks like not updating the skeleton with animations when you cannot see them (or using level streaming). If you have 100 characters, I’m assuming the AI isn’t too detailed. Could you run some of it in the Controller, instead?
Ctrl + Shift + , for GPU profiling.
Also, try this tutorial by Epic’s Zak Parrish: https://www.youtube.com/watch?v=hcxetY8g_fs
If you give us a few more details about your game, we may be able to help more. 