The two-sided medal is engraved with a Sydney skyline showing course landmarks including the Opera House, the Sydney Harbour Bridge -- and a building that closely resembles Allianz Arena in Munich.
The German arena's shape and diamond-patterned exterior seem to be reproduced in the medal instead of the flatter features of Allianz Stadium in Sydney.
"There's more to this medal than meets the eye. Every detail tells a part of Sydney," Sydney Marathon said in an Instagram post revealing the design ahead of the August 30 event.
"Look closely and you'll find the story of the course in the details," it said.
"A beautiful Sydney skyline brings the course to life, featuring the landmarks runners will experience along the way -- starting with the Sydney Harbour Bridge and finishing at the world-famous Sydney Opera House."
Sydney Marathon organisers did not immediately respond to a request for comment.
The medal's reception on social media was light-hearted.
"Oh, dear. Oh, this is bad," said Instagram account @morningcoffeerun, speculating that someone may have mixed up the stadiums in an online search for Allianz.
Munich's Allianz Arena took the gaffe in good humour.
"Oh wow, we didn't have that on our bingo card!" it posted on Instagram.
"Perhaps they tried to find something else they had in common: Allianz Arena -- Sydney Opera -- Unique Architecture -- Both are worth a visit!"
Australian media also poked fun at the organisers.
"The medal that will put Sydney on the map. The wrong map," ran a headline in the Sydney Morning Herald.
The other side of the Sydney Marathon medal shows a widely praised blue-and-gold design by Indigenous artist Ambrose Killian, who told AFP he was not involved in the creation of the Sydney skyline.
Marathon organisers say they expect a record of more than 40,000 participants who will earn the medal as a "badge of honour" for completing the 42.2-kilometre (26.2-mile) course.
"With the event a week away, this is the medal our finishers will receive," the Sydney Marathon spokesperson said.
"Behind every one of these medals is months of early mornings, long runs and quiet determination, and having it placed around your neck at the Sydney Opera House is a moment our participants will never forget," the spokesperson added.
"It's a beautiful medal, and now a little more unique."