The rumored couple spent time in Gucci before leaving in the reality star's Ferrari convertible, according to Hollywood Life.
The pair were dressed in coordinating casual ensembles of a t-shirt and jeans.
The outing followed Disick and Richie's coffee date in Calabasas and shopping spree in Beverly Hills on Friday. Us Weekly reported Sunday that the pair are "officially hooking up."
"Things became official over the past week while they were in New York City together," a source told the magazine.
"It's so weird. Not just the age difference, but mostly the fact that Sofia had been a family friend for years, and was close to [Kendall Jenner and Kylie Jenner]," the insider added, referencing the sisters of Disick's ex-partner, Kourtney Kardashian.
Disick, who shares three children with Kardashian, split from the reality star in 2015 after nine years together. People reported last week that he and Richie, the daughter of singer Lionel Richie, have been "inseparable."
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"They are spending every day together. Sofia seems smitten," a source said.
Richie had denied a romance with Disick in May after they were spotted on a yacht in Cannes.
She said in a tweet at the time, "Just so everyone can get their panties out of their [expletive], Scott and I are just homies #relax."
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