A while ago the coreboot project started to do 4 regular releases a year. It appears they are adjusting their release cycle plans a bit. Stefan Reinauer posted a message on the coreboot list with information about this schedule/cycle change, including a long FAQ. Excerpt of Stefan’s message:

“However, releases take a lot of time, and we were not able to tighten the release process with each release, as we had originally hoped, and so, after I talked with Patrick and Martin, we have decided to move to a slightly slower paced release cycle, creating only two releases per year. In turn, we will try to improve the overall quality of the releases in the future. This switch will mean, that the coreboot 4.5 release will happen in fall 2016, rather than this month.”

More info:
https://www.coreboot.org/pipermail/coreboot/2016-July/081677.html