Azure Storage did it back in October, 2017 for new objects and retroactively applied it for existing objects too as a background process.
https://learn.microsoft.com/en-us/azure/storage/common/stora...
Google Cloud storage also has it available by default, but not sure if this was always the case.
https://cloud.google.com/storage/docs/encryption
[1]: https://cloudplatform.googleblog.com/2013/08/google-cloud-st...
[1]: https://cloudplatform.googleblog.com/2013/08/google-cloud-st...