Only 14 months ago, Hahn was playing in the German third division for Kickers Offenbach.
On Friday, he received a phone call from Joachim Low's assistant Hans-Dieter Flick telling him he was part of the squad to face Chile in a friendly in Stuttgart next Wednesday.
"I thought I was being wound up," said Hahn, one of Augsburg's most impressive players in a 1-1 draw against Hannover on Saturday, in front of Flick.
"I shivered the full length of my body. My career path is anything but normal."
Rather than reporting for training with his Augsburg team-mates on Monday, the 23-year-old will take the train to Stuttgart, where he will get his first taste of international football.
The former Koblenz player did not even represent his country at youth level.
"I'm just going to savour the occasion and give it all I've got," Hahn said on sport1.de.
"It doesn't get any better than this. I'm not going to have any expectations. I'm just glad to get the chance to train with such world-class players and gain this experience."