All the 40g and 100g interfaces will be called with “et” prefix. This is in line with Junos interface naming convention.
10g interfaces will remain to be called “xe”.
If a 40g interface is channelized to 10g, it will be called xe interface with “colon” notation.
https://www.juniper.net/documentation/en_US/junos/topics/topic-map/switches-interface-port.html
On QFX5100-48S and QFX5100-48T switches running Enhanced Layer 2 Software:
The valid port range for a 10-Gigabit Ethernet interface is 0 through 47 on PIC 0. There are 48 available ports. When you channelize the 6 40-Gbps QSFP+ ports on 0 through 5 on PIC 1, there are 72 available ports.