Openai.client.files.content(files_id) does not work for any file in Assistant realm

When upload a file as part of a thread or as part of an Assistant I get an error 400 when trying to retrieve that file:

Error code: 400 - {‘error’: {‘message’: ‘Not allowed to download files of purpose: assistants’, ‘type’: ‘invalid_request_error’, ‘param’: None, ‘code’: None}}

The API docs do not mention such a limitation.