I think it essentially always has been. It was there first, [GCP copied it](https://cloud.google.com/storage/docs/xml-api/overview), [OpenStack has compatibility middleware](https://docs.openstack.org/swift/latest/middleware.html#modu...).

Yev here -> It's not so much a standard, though S3 is generally the most often used suite of APIs. 100s of integrations exist with our B2 Native APIs (https://www.backblaze.com/b2/integrations.html), but a lot of folks only know how to write to S3 Compatible APIs and don't have the resources to write to multiple API suites, so this makes integration easier for them!

Digital Ocean, OVH and others seem to use the S3 API. It does give you the benefit of clients written against S3 can now be used for your platform, and unlike a lot of AWS the API contract seems pretty reasonable and well kept.

Edit: Confused Hetzner and OVH, sorry

That's a good question to ask. S3 has become so common that it's going toward that road.

It's like brand names that become so common that people use no more the material name, but the brand.

I don't see Google, MS Azure or Rackspace switching their API anytime soon, but yes, smaller players and new ones do.