Microsoft DirectX 12 is DirectX 11 with Mantle Integrated

Sources have revealed that Direct X 12 is basically DirectX 11 with Mantle absorbed, the performance increase on Xbox One is in doubt.

NVIDIA Highlights DirectX 12 Strengths Over AMD - Legit Reviews

Testing DirectX 11 vs. DirectX 12 performance with Stardock's

NVIDIA releases first DirectX 12 Ultimate driver for developers

Microsoft announces DirectX 12, coming 2015

DirectX 12 vs DirectX 11 – How DX12 will transform PC gaming on

Why DirectX 12 is a game-changer for PC enthusiasts

AMD shows DirectX 12 performance in 3DMark benchmark

Mantle API vs DirectX 11 on Battlefield 4 – goldfries

Microsoft announces DirectX 12, coming 2015