What does controlled airspace become when ATC goes off duty?

When Air Traffic Control (ATC) goes off duty, controlled airspace does indeed become unattended, akin to uncontrolled airspace. This change implies that while the airspace still retains its classification as controlled airspace, there is no active ATC service to provide separation and manage traffic.

Pilots are still expected to adhere to the regulations associated with that airspace, but they must operate with heightened vigilance due to the absence of ATC guidance. They must follow established procedures for operating in that area, such as using position reports and maintaining proper separation from other aircraft.

The classification as uncontrolled airspace signifies that pilots are responsible for their own navigation and separation from other traffic, which is a fundamental aspect of flying in an unattended airspace scenario.