Weaker copyleft. Doesn’t guarantee freedom the way GPL does.
If someone were to make a proprietary derivative using the MIT licensed code, that would be allowed. Their source code changes aren’t required to be shared and licensed under a FLOSS license.
GPL on the other hand, guarantees (legally, not always in practice) that any derivatives are to be licensed the same way, so they must remain FLOSS.
Okay, but openai was open source once. And then they just didn’t change their name when they changed their licenses. Which I actually think is more dishonest.