The pair was first linked back in April.
"Kylie and Timothée are still seeing each other when they can. Kylie’s busy with work and traveling a lot, but they make time for each other when it works and both like each other," the source says, following false reports earlier this month that they had gone their separate ways. "They’re keeping things low key and chill for now, but get along great and have fun together."
Neither star has addressed the romance publicly nor have they stepped out together in an official capacity. In May, Jenner, 25, was spotted at 27-year-old Chalamet's home in Beverly Hills. She also attended a family barbecue with her sister, Kendall Jenner, and Timothée's sister, Pauline Chalamet, both on hand.
Jenner and Chalamet were first linked back in April, when a source told ET the couple was enjoying each other's company.
"They are keeping things casual at this point," the source said at the time. "It's not serious, but Kylie is enjoying hanging out with Timothée and seeing where it goes. It's been really fun for her because it feels a lot different than her past relationships. It's new and exciting for Kylie and she's having a lot of fun."
In June, a source confirmed the pair was still together, but moving slowly.
"They're still taking things slow," the source said. "She's enjoying this time and seeing where things go. She is being mindful of her kids as her main priority is always being a great mom."
Jenner is mom to daughter Stormi, 5, and son Aire, 1, both of whom she shares with her ex, Travis Scott.
As for Jenner and the "Sicko Mode" rapper, a source recently told ET they are working together to co-parent their children.
"Kylie and Travis are co-parenting well. They’ve both been doing their own things and doing their best to respect one another," the source said. "They get along and make their kids a priority. Kylie is a very hands on mom and involved in every way."
The source added of the rapper's current relationship status, "Travis isn’t dating anyone seriously at this point."
For his part, he's focusing on the music. Last month, Scott released a new song, "Meltdown," that some believe to be a reference to Jenner's new love life.
In the song, Scott sings "Chocolate AP and chocolate the Vs got the Willy Wonka factory/ Burn an athlete like it's calories/ find another flame hot as me, b**ch!!!"
AP is short for Audemars Piguet, a luxury watch brand favored by rappers. Fans think that this is a clear reference to Chalamet, who plays the fictional chocolatier in the upcoming film, Wonka.
The Wonka trailer was released last month, giving fans a delicious first look at the origin story of the beloved candy maker from the books of Roald Dahl.
Chalamet stars as a young Willy Wonka -- following in the footsteps of Gene Wilder and Johnny Depp before him -- and performs seven musical numbers in the film, which shows how the young dreamer came up with some of his most fantastical creations and took on the established "chocolate cartel."
Last fall, Chalamet opened up about taking on the role in a cover story for Vogue.
"This movie is so sincere, it’s so joyous," he raved. "I hate to say it, but the dream as an artist is to throw whatever the f**k you want at the wall, you know? And I guess what I’m realizing is that one’s personal life, one’s adult life, can be quite boring and the artist’s life can still be extraordinary."
See the trailer below. Wonka is set to hit theaters on Dec. 15.