Biden administration officials on Wednesday evening briefed top officials from the Trump administration on China’s high-altitude surveillance program, according to a person familiar with the briefing.

Former Secretary of State Mike Pompeo, former National Intelligence Director John Ratcliffe and former national security adviser Robert O’Brien were briefed for just over an hour by top U.S. intelligence officials at the headquarters of the Office of the Director of National Intelligence, this person said.

The briefing touched on China’s overall program, the source said, as well as past incidents of surveillance balloons’ entering U.S. airspace, including during the Trump and Biden administrations.

A spokesperson for the national intelligence director’s office confirmed that Pompeo, Ratcliffe and O’Brien were jointly briefed Wednesday evening.

The Biden administration had offered classified briefings to former Trump administration officials because incidents that occurred during Trump’s presidency weren’t discovered until after Biden took office. The one the national intelligence director’s office conducted for Pompeo, Ratcliffe and O’Brien followed a briefing Wednesday for former national security adviser John Bolton.

Bolton was sharply critical of the administration’s handling of the Chinese surveillance balloon and the three other objects that were shot down. The person familiar with the briefing for Pompeo, Ratcliffe and O’Brien, however, described it as “gracious” of the Biden administration to provide them with the briefing.

The person familiar with the evening briefing said the Biden officials confirmed that the Chinese spy balloon that lingered over the U.S. before it was shot down off South Carolina on Feb. 4 was an “unprecedented” incident and that nothing of that magnitude had occurred in U.S. airspace before then.

The briefing also included discussion about the aerial objects the U.S. military shot down over the weekend, but the briefers did not have much information about those incidents, this person said. The primary focus of the briefing was on China’s surveillance program and the past incidents of Chinese intrusions into U.S. airspace, this person said.

They added that the Chinese spy balloon raised grave national security concerns for the U.S., calling the program a “very significant platform” and noting the balloon is big enough to carry all kinds of weapons if China desires.

“This is a very dangerous game they’re playing,” this person said. “This is a very significant Chinese operation, and we have to wake up.” To that point, the source said the incident appears to have been a “wakeup call” for the administration and the American people.