This morning, I tried reserving a copy of Windows 10 on a system that packs a GTX 980 Ti and, to my surprise, found that it wouldn't show the usual "Reserve your upgrade" or "How this free upgrade works" options. Digging into the "Check your PC" portion of the app revealed why: Windows 10 apparently doesn't recognize the graphics card--even though the 980 Ti is one of the first GPUs to support DirectX 12's 12.1 feature level.
Bummer. Super mega major bummer.
Digging a little deeper revealed a several other GTX 980 Ti owners suffering from the same problem.
The issue appears to stem from the relative newness of both the card itself as well as Windows 10. The GTX 980 Ti gained support for Windows 10 with Nvidia's 353.30 driver, released over a month ago; perhaps Microsoft simply needs to update the compatibility database its app hooks into (Of note: The Windows 10 upgrade app says the "Check your PC" test was last run on June 29, as you see in the screenshot above, though I opened the app and tried reserving the copy this very morning.)
Either way, the error is preventing GTX 980 Ti owners from reserving a Windows 10 upgrade right now. Here's hoping it gets fixed sooner rather than later. But if you're impatient, this Reddit post offers a technical workaround--which I haven't personally tested--that can supposedly force Windows 10 into accepting your hardware right now.