It is definitely not open-source. They created their own license: https://github.com/antiwork/gumroad?tab=License-1-ov-file
And the tl;dr on the “suspicious timing” is that the owner seems to have gotten rid of support staff and replaced them with an AI chatbot so that he can go “work” for DOGE. Yes, really.
FOSS die-hards may not agree, but this kind of threading-the-needle can be done well, and honestly, IMHO. A good example is the content-management framework Directus, which essentially makes it free to use in most cases, unless you make more than $5 million in finances per year, at which point you need to start paying for it. Not purely open source, but it throws FOSS folks a bone by making it so that versions of the software that are more than three years old revert to the General Public License.
This has nothing to do with being a FOSS die-hard. Three year old versions are basically completely useless if you plan to run anything resembling a secure website.
Meanwhile a license that is attached to the amount of income of the legal entity (company, organization,…) instead of the project is never going to be popular because those values can easily change by reorganizations that have very little to do with the actual project.
I hate that assholes are in charge of everything.
Why should anyone care about the gumroad code anyway? The software is the least important part of running a service like that.
Alternative to gumroad?