10:22 AM PT -- 8/30 -- According to his filing, Andy wants joint physical and legal custody of their kid, and says he's going to pay spousal support. Andy also wants to split property with his wife.
In the docs, Andy is citing irreconcilable differences as the reason for the split.
Andy Richter and his actress wife are a done deal ... officially ... he just filed for divorce.
Andy filed for divorce from Sarah Thyre Thursday ... according to legal docs obtained by TMZ.
Best known as Conan O'Brien's sidekick on all three of his late night shows, Andy got hitched to Sarah way back in the day in 1996 ... and the former couple had two kids together, an 18-year-old son, William, and a 13-year-old daughter, Mercy.
Andy and Sarah called it quits earlier this year in April after over two decades of marriage ... with Andy saying their "marriage has reached its completion."
The split was pretty amicable ... Andy and Sarah said they would "always maintain a loving friendship and parenting partnership."
Andy and Sarah first met in 1991, during the production of "The Real Live Brady Bunch" ... and over the years they both appeared alongside one another on Comedy Central's "Upright Citizens Brigade" as well as "Late Night with Conan O'Brien."