The driver is not available via the normal Windows Update feature in Windows 8.1; it has to be manually downloaded via Microsoft's website. The company stated:
"The update – which is available now -- improves the mass deployment process, broadens the range of enterprise-level features, and helps bring the Surface 3 deployment experience in line with its more business-oriented sibling, Surface Pro 3. The update includes new and enhanced features including those expected in a larger-scale commercial environment such as enhanced PXE booting and support for asset tagging."
This update should help the Surface 3 be more enterprise and business friendly and could encourage more companies to purchase the tablet in the weeks and months to come.