Estner started in Italian F4 while racing full time in the ADAC F4 championship. Like in Germany, he raced with the VAR team at the 7th round of the season at Mugello where he finished 10th, 15th and 26th respectively. This gave Estner a singular point and 27th in the championship. In 2019 Estner returned once again for only one round, however this time it was at Imola. His best finish was 9th in the first race however in the next 2 he failed to score and in the 4th and final race he didn't start. He bettered his total from last year by one point.
ADAC F4
Estner started his Single Seater career in 2018 alongside his brother Andreas in the Austrian outfit Neuhauser Racing. They both competed in the first 5 rounds of the season before jumping over to the Italian F4 Championship. Sebastian's best finish was 10th which turned out to be his only points scoring position all season. Esnter returned to the ADAC Formula 4 in 2019 but this time with Dutch team Van Amersfoort Racing. During the first 3 races, Esnter finished in the points 3 times, his best finish being 9th. At the 3rd race at Zandvoort, starting on reverse-grid pole, Esnter won his first ever single seater race. Most of the race he was fending off Swiss driver Grégoire Saucy. Arthur Leclerc spun after making contact with Ido Cohen, when rejoining Leclerc colided with teammate Roman Staněk, this bought out the saftey car. After the saftey car restart French driver Alessandro Ghiretti overtook Saucy and put late pressure on Estner. Estner shared the podium with the two drivers who put pressure on him that races, Ghiretti and Saucy. The second half of the season saw Estner's results pick up with four points finishes in a row, highest position was 5th. However as he raced further up the grid he also started interfering with the race for the championship, colliding with eventual champion Théo Pourchaire multiple times in the later stages of the season. Estner finished the season in 14th with 55 points, one place behind Israeli teammate Cohen trailing him by 21 points.
Euroformula Open
On March 1 it was annonced that Estner would partnering French driver Alexandre Bardinon for Van Amersfoort Racing in the 2020 Euroformula Open Championship. It was later confirmed that, once again, the Estner Brothers would be racing alongside eachother for the up coming season.
