Airbnb has closed on a more than $1 billion round of funding, a source close to the company told CNBC. The round was confirmed in an&nbsp;SEC filing that dropped on Thursday. It is now worth approximately $31 billion. The company raised roughly an additional $450 million as part of its Series F round, making the round nearly twice as much as it stood last fall. The total amount raised was $1,003,312,065, according to the filing.