On EX4400 the 100G interfaces are not coming up.

These 100G ports are set up by default as 50G Virtual Chassis ports.

If you are not using an EX4400 switch as a member switch in a Virtual Chassis, you can use a command with the network-port option to enable network port mode, which converts the default VCPs on the switch into network ports. By default, the two 100-Gigabit Ethernet QSFP28 ports on the rear panel are set as two logical 50-Gbps VCP interfaces each, forming a total of four logical 50-Gbps VCPs. (The default VCPs are in PIC slot 1, so the VCP interfaces are named vcp-255/1/0 through vcp-255/1/3.)

If you convert these ports into network port mode, they become two 100 Gigabit Ethernet network ports, or you can channelize each of them into four 25-Gigabit Ethernet or four 10-Gigabit Ethernet network ports.

On Juniper Networks EX4400 series use the following command to enable 100G interfaces:

>request virtual-chassis mode network-port

Then, reboot the switch and use the command > show interfaces terse to confirm the interface is now detected