“New kid, who dis?” the actress, 37, captioned the post, which had nearly 600,000 likes as of late Friday morning.
“Congratulations,” commented actress Eiza González.
“Welcome to never sleeping again,” one fan wrote in response.
“You look so different and wonder-filled. You are going to funnier and more poignant than ever,” said another.
“The best! Enjoy every second of him....the days are long, but the years are short,” one person advised.
Schumer on Monday announced the birth of her and husband Chris Fischer's son, whose middle name appears to be a nod to friend and comedian Dave Attell.
“10:55 pm last night. Our royal baby was born,” she captioned the Instagram post, referencing Duchess Meghan and Prince Harry’s newborn who they welcomed on Monday.
Schumer and Fischer were married in February 2018 — just days after the duo made their relationship official on social media. Eight months later, Schumer revealed she was pregnant with the couple’s first child.
Fox News' Katherine Lam contributed to this report.