Will a Windows 10 key work on Windows 11, and the other way round?

In most cases yes, as long as the edition matches.

The main rule: same edition

A Windows 10 Pro key activates Windows 11 Pro. A Home key activates Home.

Does it work the other way?

Generally yes: a Windows 11 key usually activates Windows 10 of the same edition.

Three common cases

• Same PC, upgrade: activation carries over automatically.
• Clean install on the same PC: it reactivates online.
• New PC: works for Retail, not OEM.

Keys for Windows 7 and 8

Microsoft ended that free upgrade path, so do not count on these keys.

What can get in the way

The PC must meet Windows 11 requirements, and an OEM licence stays with its device.