Earlier today, Microsoft released Windows 10 Insider Preview build 15055 to the Fast ring for both PCs and phones. Slow ring users are getting some love as well, as the company is offering build 15051, which was originally released to the Fast ring earlier this week.
15051 replaces 15043, which was only introduced to the Slow ring eight days ago, and was also the first new Windows 10 Mobile build in the ring since November. Two days ago, PC users got their first Slow ring build since December in 15048.
The difference in time between builds 15043 and 15051 is worth noting, because the Slow ring typically gets new releases monthly, while Fast ring is weekly; however, both of them have been more frequent as of late. This is yet another sign that the Creators Update is near completion, as it's scheduled for general availability in April.
If you were on the previous build, you won't notice any new features in this one. There are some fixes and known issues, of course. In fact, there's an issue that will cause background tasks to not run, which is also present in today's Fast ring build. Microsoft says it will fix it in the next update.
If you're on the Slow ring, you can get today's build by heading over to Settings -> Update & security -> Phone update -> Check for updates. If not, you can go to the Windows Insider Program tab and tap 'Get started'. Once your phone reboots, go back and set it to the Slow ring.