no, the extension on the "GET /" endpoint will always be optional. mainly because its not important to the server, its mostly there just to allow the client to have a hint at file type so it can show an image / video / pdf viewer

Although I'm going to open a PR tomorrow to make the file extension required on the "url" field returned from the /upload /list and /mirror endpoints. since that field is intended to be used by the client and the client generally needs the file extension