Terraform uses SDKs for interacting with provider APIs. There isn’t a distinction to be made for Terraform. You just bump the SDK version and it’s down to the individual provider APIs ‘under the covers’ to handle versioning. So in that case I looked at the top providers listed on https://registry.terraform.io/browse/providers which are AWS, Azure and Google Cloud Platform.
AWS versions its APIs using a versioning system based on the format “YYYY-MM-DD”. The YYYY-MM-DD format is based on the date of the API release. Each API has its own version number, which is incremented with each new release.
For example, an API released on January 1st, 2020, would have a version number of “2020-01-01”.