Sixteen drivers from the current grid will take part in this week's two-day post-race test in Bahrain, including championship rivals Sebastian Vettel and Lewis Hamilton.
Seven teams, however, will devote at least some part of the two days to running new faces alongside their 2017 regulars, with the only exceptions being Mercedes, Haas and Sauber.
Ferrari, for example, will field reserve driver Antonio Giovinazzi on day one, with Vettel taking over for the second day - although the four-time champion and current points leader will also be in action on the first day as part of Pirelli's 2018 tyre development programme.
Red Bull will split their time between Daniel Ricciardo and Pierre Gasly, who beat Giovinazzi to last year's crown in what is now the newly-renamed Formula 2 championship.
At Force India, reserve driver Alfonso Celis will be on duty for the opening day, before handing over to Sergio Perez.
Williams have opted to split the first day between 2017 racers Lance Stroll and Felipe Massa, with former McLaren test driver Gary Paffett taking control of the FW40 on day two.
At Toro Rosso, meanwhile, F2 driver Sean Gelael will get his first taste of F1 machinery on day one, before Daniil Kvyat takes over on Wednesday.
Test drivers will also get some mileage at McLaren and Renault - Oliver Turvey will be in action for the former on day one, while Sergey Sirotkin will drive for the latter on day two.
Look out for a full report and images from Tuesday's action in Bahrain at the end of the day, or for minute-by-minute timesheet updates from Sakhir, download the Official F1® App and go to Results & Standings > TEST. For more information, click here.