When it was clear McLaren had missed its targets for the start of the season, it decided to roll out a three-pronged upgrade plan to get the MCL60 to the level the team believes it should be, having debuted a draggy specification in Bahrain.
The first package of updates was launched in Baku, and while the team was satisfied it produced the expected results and correlated well with its wind tunnel data, the car still proved excessively draggy and off the pace compared to some of its midfield rivals.
Earlier this year Stella revealed that McLaren's biggest upgrade package for 2023 was readied for launch before the summer break and amounted to "kind of a B-spec".
That substantial revamp has now been signed off by the Woking team's design departments and is heading for production, with a planned rollout at either the Austrian or British Grand Prix in July.
Team principal Stella said the car would look "noticeably different" but would be an evolution of McLaren's current concept rather than a Mercedes-like change of approach.
"The plan is we need to get the car more competitive. We've now released the package which should be available between Austria and Britain, and this is what should take the car to a more competitive level," Stella said.
"It's progressing the car, evolving concepts we see as successful. It will be noticeably different to what we have at the moment.
"It will be the foundation for future developments next year. For the second part of the season there should be another major upgrade."
The Austrian Grand Prix is F1 2023's second of six sprints featuring just a single hour of free practice, but that is not thought to be a deal-breaker if the new specification is ready in time.
Stella hopes this weekend's Spanish Grand Prix at Barcelona should suit the current version of the car with its high-speed sweeps but cautioned that McLaren's lack of aerodynamic efficiency is still a priority to be addressed.
When asked if McLaren is currently relying on perfect execution to score points, he replied: "You can have high-quality execution but on tracks where you can overtake, ultimately you need the pace.
"Let's see. Hopefully Spain, with some high-speed corners, suits our car better. But we know we need to improve aerodynamic efficiency and that's what will happen in a couple of races."
Drivers Lando Norris and Oscar Piastri scored minor points in Monaco with a ninth and 10th place respectively. That left McLaren sixth in the constructors' standings, while seeing midfield rival Alpine break clear by virtue of Esteban Ocon's shock podium.
Additional reporting by Stuart Codling
