Roddy Ricch and his ex-girlfriend Alexandra Kiser have reached a custody agreement for their 3-year-old son ... finally putting an end to their parental tug-o-war.

"The Box" rapper will have joint legal custody and is getting physical custody of the kid for a couple days each week from Tuesdays to Thursdays.

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He also has to pay Alexandra $8K a month in child support ... on top of their son's private school tuition, medical bills, any special-needs therapy, and additional extracurricular activities.

Roddy also agreed to pay $37,500 for Alexandra's legal bills, and will need to fork over another $1K in a monthly stipend for her to get a car.

His attorney, Samantha Spector, negotiated the terms of the settlement, which was filed Friday in L.A. County.

Sources connected to the ex-couple tell us they're in a very good place now when it comes to co-parenting -- which is a dramatic turnaround. Alexandra had previously filed docs alleging the Diamond-selling artist wasn't taking care of his fatherly responsibilities with what she claimed was his $25 million net worth.

Now that the custody case is behind him, Roddy will likely resume his rap career.

DJ Hed has been teasing that the Compton MC is sitting on musical heat for nearly a year ... and summer is right around the corner!!!