Relicensing from Apache-2.0 to Apache-or-MIT

Question

I'd like to relicense one of my projects from Apache 2.0 to Apache-or-MIT dual license for consistency with the outer community (Rust — see here), and to allow GPLv2 compatibility, which I was previously unaware was disallowed by Apache.

From what I understand, it is necessary to get approval from all contributors to migrate from MIT to Apache, as that implies contributions are providing the Apache 2.0 patent grant:

Requiring both MIT and Apache 2.0 as inbound licenses for contributions means that anyone making a contribution is providing the Apache 2.0 patent grant. And then having MIT and Apache 2.0 as outbound licenses people can use Rust under means that Rust provides widespread compatibility with all sorts of other FOSS licenses, including GPLv2.

But what about the inverse? Since MIT is mostly a subset of Apache, and the dual MIT license is there just to serve as an outbound license that allows GPLv2 compatibility, does the conversion from Apache to MIT still require approval from all contributors?

Answer 1

The rules are very simple: If you want to relicense a project, then you need approval from all the copyright holders.

It does not matter here that the MIT license is mostly a subset of the Apache license. They are different licenses and if you want to change the license under which the project is offered, you need permission.