Fahrenheit was an effort to create a unified high-level API for 3D computer graphics to unify Direct3D and OpenGL. It was designed primarily by Microsoft and SGI and also included work from an HP-Microsoft joint effort.

Direct3D and OpenGL are low-level APIs that concentrate primarily on the rendering steps of the 3D rendering pipeline. Programs that use these APIs have to supply a considerable amount of code to handle the rest of the pipeline. Fahrenheit hoped to provide a single API that would do most of this work, and then call either Direct3D or OpenGL for the last steps.

Much of the original Fahrenheit project was abandoned, and Microsoft and SGI eventually gave up on attempts to work together. In the end, only the scene graph portion of the Fahrenheit system, known as XSG, saw a release and was discontinued shortly afterwards.

In the 1990s SGI's OpenGL was the de facto standard for 3D computer graphics. Prior to the mid-90s different platforms had used various custom solutions, but SGI's power in the graphics market, combined with the efforts of the OpenGL Architecture Review Board (ARB), led to the rapid standardization of OpenGL across the majority of the graphics workstation market. In the mid-1990s, Microsoft licensed OpenGL for their Windows NT operating system as its primary 3D system; Microsoft was positioning NT as a workstation-class system, and OpenGL was required in order to be a real competitor in this space. Initial support was released in Windows NT Workstation version 3.5 in 1994.

Confusing matters was Microsoft's February 1995 purchase of RenderMorphics. Their Reality Lab product was a 3D library written specifically for gaming purposes, aimed primarily at the "low end" market. After renaming it to Direct3D 3.0, Microsoft released it as the primary 3D API for Windows 95 and game programming. This sparked off a massive debate, both within Microsoft and outside, about the merits of the two APIs and whether or not Direct3D should be promoted.

Through the mid-90s SGI had been working on a series of efforts to provide a higher level API on top of OpenGL to make programming easier. By 1997 this had evolved into their OpenGL++ system, a retained-mode C++ API on top of OpenGL. They proposed that a modified version be used as a single API on top of either OpenGL or a new high-performance low-level API that Microsoft was known to be working on (not based on Reality Lab). This would not only hide the implementation details and make the OpenGL/DirectX war superfluous, but at the same time offer considerably better high-level interfaces for a more robust object oriented development environment.

The OpenGL++ effort dragged on in the ARB through 1997. Although SGI committed resources to the project in order to provide a sample implementation, it appears they were unhappy with progress overall and complained "There's been lots of work, but relatively little communication." Microsoft in particular had stated in no uncertain terms that they would not be supporting the effort, and SGI felt that their support would be essential for any efforts moving forward.

A joint press release in December 1997, followed by an announcement at an ARB meeting in early 1998 by SGI, announced that work on OpenGL++ had been abandoned and SGI had partnered with Microsoft to produce a new system code-named "Fahrenheit". SGI was to provide the primary "mid-sized" API used in most applications, Fahrenheit Scene Graph, as well as a modified version for handling very large models from CAD applications, Fahrenheit Large Model. Microsoft would provide a new low-level rendering engine for Windows known as Fahrenheit Low Level, essentially a replacement for the Reality Lab-based version of Direct3D. The project was officially announced at SIGGRAPH 1998 for release in late 1999 or early 2000.