An early Windows 11 version was made available to members of the Windows Insider program. More specifically, Windows 11 requires Intel 8th Gen Coffee Lake or Zen 2 CPUs and up, TPM 2.0, 4GB of RAM, and 64GB of storage.
We've talked about the Windows 11 system requirements elsewhere - but, this time, Microsoft said you can only install it on processors made from roughly 2016 to 2017 onward.
Pocket-lint has a detailed guide that explains all the new features in Windows 11.