In the photo, dozens of red heart-shaped balloons covered the ceiling of their home.
The supermodel and "America’s Got Talent" judge also shared two other photos and a short video of the couple kissing and nuzzling.
HEIDI KLUM, 49, REVEALS IF SHE'D HAVE ANOTHER BABY AND THE WILD THING SHE'D DO NAKED
Heidi Klum and Tom Kaulitz were married on Feb. 22, 2019. (Photo by Jeff Kravitz/FilmMagic)
Another photo showed two cakes, including a sprinkle-filled one that said "4 years" and the last photo was a closeup of a bouquet of roses and the ceiling-clinging heart-shaped balloons.
Heidi Klum shared a kissing selfie with her husband Tom Kaulitz for their fourth anniversary. (Heidi Klum/Instagram)
Earlier this month, Klum, 49, told Jennifer Hudson on her talk show that it "depends on what day it is" on whether she’d like to have a baby with Kaulitz, 33.
The model shares four children with ex-husband Seal.
Heidi Klum with her oldest daughter Leni. (Photo by ANGELA WEISS / AFP via Getty Images)
Her eldest daughter, Leni, 18,was adopted by Seal upon her birth. They also share sons Henry and Johan, as well as daughter Lou. The couple separated in 2012 after seven years of marriage, and were divorced in 2014.
Their other children are 17, 16 and 13.
Kaulitz, who is stepdad to her kids, has no biological children of his own.