Romain Grosjean and Kevin Magnussen have each confirmed they will leave Haas at the end of the 2020 F1® season as speculation mounts about the identity of their replacements.
Grosjean signed for Haas in 2016 when the team joined the series but has largely struggled to build on his promising performances at Lotus, where he had 10 podiums.
Meanwhile, Magnussen moved from Renault a year later and has likewise been unable to provide any serious challenge to the sport's elite, although he finished an impressive ninth in 2018.
The departure of the pair had appeared inevitable long before Thursday's announcement.
Grosjean came ninth last time out at the Eifel Grand Prix, his best performance for more than a year, but Haas principal Guenther Steiner subsequently said the team could not be "emotional" and decide "race to race" on their future.
A host of names have been linked with the vacant seats, among them Mick Schumacher - son of Michael - who is also said to be an Alfa Romeo target.
Schumacher was set to make his F1® debut with Alfa in practice in Germany until adverse weather conditions intervened.
Sergio Perez, Nico Hulkenberg and Nikita Mazepin - another F2 contender, like season leader Schumacher - have been mentioned as potential Haas signings.
Grosjean wrote on Twitter on Thursday: "The last chapter is closed and the book is finished.
"I've been with Haas F1® team since day 1. Five years during which we went through highs and lows but the journey was worth it.
"I've learned a lot, improved to be a better driver as well as a better man. I hope I've also helped people in the team to improve themself.
"This is probably my biggest pride, more than any of the crazy first races in 2016 or the P4 at the Austrian GP 2018.
"I wish the team all the best for the future."
Magnussen said: "The 2020 Formula 1® season will be my last with Haas F1® Team. I have had a great time with the team for four years and I look back at a great journey.
"Being part of a brand new team has been a challenge that I have thoroughly enjoyed and it has brought me a huge amount of experience that has helped me grow and develop as a racing driver.
"I would like to thank Gene, Guenther and all of the race team for their loyalty and trust in me over the past four years.
"I am still working on my plans for the future, which I will announce in due course.
"There are still six races to do this season, and I am determined to give my all to finish off on a high. Thank you all for your support."