The last official build that was released to Insiders before the January Technical Preview was build 9879, along with some minor fixes that followed soon after that. Microsoft explained at that time that they were taking a break over the holidays, but we know that internally they were compiling a lot of new builds, and by the time they released build 9926, build 10000 was already a thing of the past.
Why did Microsoft choose to wait so long before releasing the new build? The answer is quite simple. They wanted to align the release with their January press conference, and they also wanted to build up excitement and anticipation from Insiders, while they secretly prepared a lot of new features to blow us away at the event. And they sure did.
Not too long ago someone asked Gabe Aul if there would be faster releases, and he confirmed that we will no longer be dealing with long waits like the two months between build 9879 and build 9926. He also added that the cadence will increase as they get closer to the final version.
This means a big number of Insiders will get to test out new bits more frequently, and more feedback will get to the ears of Microsoft engineers. Gabe also confirmed that users will be able to upgrade "all the way with each build until the final release". Not only that, but the next build might be closer than you think:
There are a lot of new things in build 9926, and if you need a refresher, you can check all of our coverage here. If you happen to find something that we have not covered yet, make sure to send us a tip. Or, if you are having issues with your install, you can get help in our forums here.
Source: Gabe Aul