The rapper and the model recently spent his birthday together in France.
"Kanye and Irina's relationship was never serious and the two of them have always just been having fun together," the source says. "They're both doing their own thing and down to have a good time without any strings attached."
West, 44, and Shayk, 35, were first spotted together last month, celebrating the rapper's birthday in Provence, France.
At the time another source told ET that the pair has "casually been seeing each other," and has "been friendly for a long time."
As for Yeezy's ex, Kim Kardashian West, another source says the 40-year-old reality star is "happy" for West and Shayk.
"At the end of the day, Kim just wants Kanye to be happy," the source said at the time. "She knows how incredible of a man he is, their relationship just ran its course and he deserves to be with someone who makes him happy."