ADPUL claims:

http://www.ultralight-glider.fr/en/biggest-competition-task-launched/

The biggest competition task ever launched.

The biggest Free Flight task* ever launched in the world Despite medium flying
conditions: a 306km task, with 83% pilots at goal. Arrival order: Manfred,
Jacques, Philippe, Ernst, Roger; Pavel landed out in Dévoluy. * closed circuit
competition task.

The headline is misleading. Of course, the longest hang gliding
task ever called and made was called an made right here in Big Spring, Texas.
Goal 215 miles (346 km) to the north. And we are not taking Swifts here.

http://ozreport.com/12.154#0