Firstly, O'Sullivan will get a run out during the Abu Dhabi Grand Prix weekend, driving in Free Practice 1 for the British team.
Already announced to be graduating to Formula 2 next year with ART Grand Prix, the 18-year-old will be taking over the reigns of Alex Albon's FW45 at the Yas Marina Circuit as part of their two mandated rookie driver sessions.
“I’m really excited to participate in FP1 at Abu Dhabi," said O'Sullivan. "I can’t wait to get behind the wheel of the FW45 for the first time and get some good mileage under my belt.
"In addition to that, I’m returning to the car for the post-season rookie test to further my development with the team. Huge thanks to Williams Racing for the opportunity and for putting their faith in me to drive the 2023 car.”
Additionally, both he and Colapinto will be in action during the end-of-season F1 Young Driver Test, sharing driving duties across the day. It will be the Argentinian's first experience in F1 machinery, straight off the back of his Formula 2 debut with MP Motorsport for the season finale.
Colapinto added: “I am extremely grateful to Williams Racing for giving me the opportunity to drive an F1 car in only my first year in the Academy. I’ve been dreaming of this day since I was a kid and have been working really hard for this.
"To have this chance at the official young driver test is a real honour. Thank you to the team for entrusting me with the FW45. Being part of the Academy this year has opened my eyes in so many different areas and I feel ready to make this step. I can’t wait.”
O'Sullivan and Colapinto both concluded their second Formula 3 seasons tied for the all-time record for most wins in the Championship, on four apiece. Driving for PREMA Racing, O'Sullivan earned two Feature Race wins, two Sprint Race victories, a further podium finish and one pole position on his way to becoming Vice Champion.
Colapinto secured two wins this season to add to his tally and claimed five podium finishes on his way to finishing fourth in the Standings for MP Motorsport.
Williams Racing Sporting Director, Sven Smeets, concluded: "Both Zak and Franco have had impressive seasons in Formula 3 and we’re now looking forward to giving them the opportunity to drive the FW45 in Abu Dhabi to aid their development as part of their roles in the Williams Racing Driver Academy.
"The pair have demonstrated a high level of understanding and maturity during their simulator work conducted at Grove. I know they'll both be working hard in preparation for this experience and will make the most of it."