As you may know, Arch Linux is among the most popular rolling release Linux systems. On April 14, Arch has received a major kernel upgrade, replacing Kernel 4.4.5 with Kernel 4.5, which has been added to the Testing repositories some time ago.
The Arch developers have skipped the Kernel 4.4.6 and Kernel 4.4.7 and adopted kernel 4.5 directly. Among others, Kernel 4.5 brings better support for AMD Radeon GPUs, comes with support for the AMD PowerPlay power management technology and brings enhancements to the AMDGPU open-source driver.
If you want to get the latest Kernel version on your system, run:
$ sudo pacman -Syu