London Heathrow’s new Terminal 2 will officially open June 4, following a £2.5 billion ($3.8 billion) upgrade, Star Alliance has confirmed. United Airlines will be the first carrier to arrive at the revamped terminal.

According to Star Alliance, 23 of its members will operate to London Heathrow, the highest number of alliance carriers coming together at any airport. About 12 million Star Alliance passengers are expected to pass through Heathrow annually.

Currently, Heathrow handles 121 Star Alliance flights per day to 45 destinations in 25 countries.

The new T2 can handle 20 million passengers annually, “but the terminal is designed to expand if necessary,” Star Alliance VP-customer experience and technology Justin Erbacci said during a media briefing.

Erbacci said the alliance is “expecting a dramatic reduction of operation costs for our member airlines,” which became part of the synergies of having all member airlines under one roof.

“In the last two years, we have worked very hard to bring all the airlines together in the terminal,” Erbacci said, adding that no one else in the industry has achieved a project like this.

Star carriers, which are currently spread out over three Heathrow terminals, will be transferred to T2 from June 4 through October.

Aer Lingus, Germanwings and Virgin Atlantic Airways will also operate from T2.

T2, which was Heathrow’s first terminal, closed after 54 years of service in 2009 and was demolished in 2010. The new T2 is the latest phase of an £11 billion transformation of Heathrow.