In 2018 Caldwell switched to the Italian outfit Prema Powerteam, partnering Enzo Fittipaldi and Gianluca Petecof for the entire season.

However, a dominant weekend at Vallelunga, where the Brit scored all three victories after qualifying on pole for every race, gave him a fighting chance for the season finale at Mugello.

At the start of the race Caldwell made contact with Andreas Estner, which later caused him to retire due with front wing and tyre damage.

[34] In January Caldwell was announced by Trident as one of their three drivers for the 2020 Formula 3 season, partnering the experienced pairing of David Beckmann and Lirim Zendeli.

In November 2021 Caldwell announced that he would be joining Campos Racing to partner Ralph Boschung in the final two rounds of the FIA Formula 2 Championship.

At the Red Bull Ring however, Caldwell would get up to eleventh by the end of the race after starting last, which eventually became sixth after penalties ahead of him had been handed out.

[50] Near the race's end, he also committed a track limits infringement, earning him a twelfth penalty point and excluding him from the round at Spa.

In the feature race, he took advantage of a pileup at the Safety car restart to finish ninth, having held off attacks from Jehan Daruvala, and was elevated to eighth following a penalty ahead.

[68][69][70] In early 2020 it was confirmed that the Brit would drive alongside Marvin Kirchhöfer and Luca Ghiotto in the Bathurst 12 Hour race for R-Motorsport.

[72] On 3 November 2021 it was announced that Caldwell would be making his debut in the FIA World Endurance Championship, driving alongside Miro Konôpka and Nelson Panciatici for the ARC Bratislava team in the 8 Hours of Bahrain.

The following year, Caldwell competed in the series' rookie test at Bahrain in November, driving the Richard Mille Racing Team LMP2 car during the afternoon session.

[81][82] Caldwell would be handed qualifying duties at Spa, where he managed to place himself ahead of Charles Milesi in the sister car, before contributing to take eighth on a damp track on Saturday.

Having defended fourth against Ben Barnicoat for a number of laps, Caldwell took third place during his second stint as a result of an accident ahead, and held the spot until leaving the car at midnight.

During the same year, the Briton also raced in the European Le Mans Series with Inter Europol Competition alongside Jonathan Aberdein and Rui Andrade.

[90] Caldwell qualified fourth and - in spite of a drive-through penalty caused by contact from Andrade and an emergency fuel stop under safety car conditions - helped his team to score a podium finish in the LMP2 Pro class.

[1] At the season-opener in Barcelona, the Briton charged into the lead during his stint, using traffic to pass Ritomo Miyata, before a quicker pit stop ended up dropping APR back to second, the position in which they eventually finished.

[100] The Brit and Kaiser would be joined by Roman De Angelis for the 24 Hours of Le Mans, as Alex Lynn attended to his Hypercar duties with Cadillac.

[102] The European season continued with eighth place at Imola, where a poorly-timed virtual safety car forced the team to play catch-up during the final hour.

[103] More misfortune befell Algarve Pro at Spa, as they finished several laps down after collecting the spinning GT Ferrari of John Hartshorne in the first stint.

[104] Despite Caldwell being overtaken for the lead by Macéo Capietto during a safety car restart at Mugello, an undercut on Panis Racing allowed the outfit to claim their second podium of the campaign, finishing second.

[106] Caldwell remained at the team for the Asian Le Mans Series held during the winter, driving alongside Alex Quinn and amateur-ranked Kriton Lendoudis.