Since both the Windows 10 and Windows 10 Mobile are officially launched, Microsoft has started internal development of Windows 10 "Redstone." Windows 10 will first get the Threshold 2 update, which will then be followed by the second update codenamed Redstone.
The Threshold update will include a small number of improvements, including Messaging app, Edge extensions, some under-the-hood improvements and other tweaks that were originally slated for the Windows 10, but due to not having enough time, they never made it.
The second update is the Redstone, which will bring more changes and improvements. It has entered early development, but it is still too early to talk about changes.