From Fedora Project Wiki
Installation Notes
Anaconda is the name of the Fedora installer. This section outlines issues related to Anaconda and installing Fedora 25.
Ext4 for boot partitions
Although ext4 was the default file system in Fedora 11, the version of the GRUB bootloader included with Fedora 11 could not read ext4 partitions. Fedora 11 therefore required a separate ext3 boot partition. The version of GRUB included in Fedora 12 now supports ext4, so anaconda now allows you to place /boot on an ext4 partition.