At the Italian Grand Prix, Honda ran its Spec 4 power unit with all four cars for the first time which brought significant changes to the combustion system, along with a brand new fuel composition from partner ExxonMobil. The engine proved to be a significant step up in performance with Tanabe labelling it a bigger step forward than the Spec 3 RA618H engine from 2018 at Toro Rosso, which at the time brought their largest performance increase since returning to F1 in 2015. This specification is widely regarded as what brought Honda up to or possibly beyond the same level as Mercedes with the two manufacturers' advantage over each other swapping circuit to circuit. A notable event was Pierre Gasly and Hamilton's straight drag to the finish line at the Brazilian Grand Prix, which showed the Toro Rosso to slowly pull ahead to finish second, scoring Honda's first 1–2 finish since the 1991 Japanese Grand Prix after Verstappen took victory from pole position.