Already having raised $850million, Telegram is reportedly holding a second pre-ICO private sale aiming for the same ammount.
This would total $1.6 billion, before the ICO has even been held. To put this into perspective, Tezos, with a happy second place in the biggest ICOs of all time rakings, have raised a total of $232 million.
https://www.theverge.com/2018/2/21/17037606/telegram-open-network-app-ico-cryptocurrency-ton