I see a lot of misinformation regarding what you can do with the Telegram APIs on this thread. I do not know the reason behind OP needing to scrape groups for users, but I do have a bit of experience with both of Telegram's APIs. The Bot API, which is the one that lets you create a bot that can join group chats easily, does not allow in any way to obtain all of the users for a group until they send a message or enter/exit the group. On the other hand, the Telegram Client API does allow for this; however, this is much more different than the bot API. The Telegram Client API is meant to be implemented in Telegram clients and does not facilitate bot usage. This is done to prevent spam, which is something that OP might actually be looking to avoid. That being said, it is perfectly possible to do so by just using the latter API, just not as easy.