As of last week, Microsoft has released updates for Windows Technical Preview build 9926. These updates for the current preview of Windows 10 on the computer are intended to prepare the transition to the next build.
As mentioned earlier, the latter was not published in the process but Microsoft had indicated a probable availability before the end of February. So we can count on it by the end of this week.
The Russian hacker WZor has just published several captures of a build 10022 of the Windows 10 preview, and therefore proof of close availability. However, they don't say much about what's in there. And if going from 9926 to 10022 (or more) may suggest a big jump, it will not necessarily be the case.
The only pretty sure thing about the next build of Windows 10 is that it will bring the Start Menu transparency effect (which was previously released in January). However, we do not know if the browser codenamed Spartan will be present. It is however noted that it will actually be offered in a preview.
There is also uncertainty about the availability of Cortana in a language other than English. The digital assistant continues to learn French in particular.