This is according to Telegram’s founder Pavel Durov where he posted that the company will start introducing ads to its platform, but in a limited capacity so that it doesn’t get in the way of its usability.
According to Durov, “Telegram will not show promotional messages in your chat list, private conversations or groups. Advertising will affect only large channels – services where there is already advertising, and the support of which leads to the greatest costs on the part of Telegram.”
The company had previously attempted to monetize itself by launching a cryptocurrency operation, but it seems that those plans fizzled out which is why the company has opted to go back to a more traditional model. Since these ads don’t appear in private groups or individual conversation, it shouldn’t impact users too much. Only those who use and participate in large channels will probably be affected, so unless that’s you, this shouldn’t be an issue.