Raspberry Pi default firmware upgraded to Linux 4.1 as the latest stable kernel.
Linux 4.1 brings many new features and improvements and is now served as the kernel for the Pi’s default firmware. The source had been available for a while already with some RPi-focused Linux distributions like OpenELEC already having opted to utilize it for the newest Linux kernel capabilities.
The default source tree on https://github.com/raspberrypi/linux is now rpi-4.1.y. This tree is now considered the stable kernel source tree and will merge in minor bumps to the kernel version, rather than rebase.
There is now a 4.2 kernel tree where more experimental kernel commits may go (in general moving closer to upstream).
More details on the kernel upgrade via this RaspberryPi.org forum thread.