On FortiGates with NP6 or NP6lite processors, the first packet of a session determines if the session can be offloaded. As long as there is no proxy-based UTM/NGFW, if your FortiGate includes NP6 processors, most sessions can be offloaded to them.
Access Control Lists (ACLs) use NP6 offloading to drop IPv4 or IPv6 packets at the physical network interface before the packets are analyzed by the CPU. The ACL feature is available only on FortiGates with NP6-accelerated interfaces. ACL checking is one of the first things that happens to the packet and checking is done by the NP6 processor. The result is very efficient protection that does not use CPU or memory resources.