Microsoft has been quite busy lately, rolling out Windows 10 Mobile build 10549 to Insiders, and build 10565 for desktop to both the Slow ring and the Fast ring along with its ISO files. Now, the company has pushed out a patch to members enrolled in the Insider Preview as well.
KB3103470 which has been identified as the "October Update for x64-based Systems" brings improvements to the overall functionality of Windows 10, as detailed on the company's support page. While Microsoft hasn't exactly expanded fully on what these improvements are, the details it does offer relate mainly to the Notepad app.
This is in line with the company's previous comment where it stated that it would detail only "significant" KB patches in the future. This is somewhat understandable, given that the majority of users don't care enough to see what every single minor update contains, and what little information the company does provide for some KB patches is usually sufficient to gain a basic idea about what the update addresses.
You can download KB3103470 via the Windows Update process.