AMD Support now offers downloads of new version 15.7 Catalyst reference drivers for AMD graphics cards running under Windows, noting these offer support for the imminent Windows 10 and DirectX 12 (thanks HARDOCP). Here's word:

Windows® 10 Support
This is a Technical Preview driver with full WDDM 2.0 support for Windows® 10 and DirectX® 12 on all Graphics Core Next (GCN) supported products, -AMD Radeon™ HD 7000 and newer graphics products. Official driver support for AMD products will be available when Microsoft launches Windows® 10 on July 29th, 2015.

NOTE: To ensure stability, users should upgrade to the latest available Windows® 10 Technical Preview build provided by Microsoft before installing AMD Catalyst™ 15.7.