Gabby Thomas has more bling than just her Olympic gold medals ... the track star is engaged after her man got down on one knee and popped the question -- and the rock is massive!
Gabby and her fiancée Spencer McManes announced the amazing news on Tuesday ... revealing he proposed during a staycation in Texas.
McManes -- founder of drink brand Kaviva -- picked a romantic spot ... the rooftop of an Airbnb where they were staying.