You can however for now use wrappers which are not harnesses such as T3Code though. They were going to cut under the Programmatic API, but have at least temporarily walked it back.

Don't use providers that don't allow it.

You absolutely can; they are not banning anymore. The bigger problem is that subscription versions of the models are way crappier than when the "same" model is hit via API (Bedrock/Vertex)

You can also make it not count against extra usage.

OpenCode docs show it because Anthropic specifically ambushed them with a PR to remove support so simpletons can't use it easily.