The car features an eye-catching red and carbon black livery designed by Alfa Romeo's main road car styling department, without the white that has been part of the established look since the company first joined forces with Sauber as a sponsor in 2018.
Alfa Romeo's deal with the Swiss organisation ends this year prior to two transition seasons with Ferrari power before the team becomes the works Audi outfit in 2026.
The new livery marks both Alfa's final fling in F1 and the switch of title sponsor from Orlen to Stake.
The team unveiled a show car at a launch event in Switzerland on Tuesday morning, as well as issuing CGI images. The real C43 will be seen for the first time when it undertakes a filming day in Barcelona on Friday.
Gallery: Alfa Romeo C43 launch 2023
New Sauber CEO Andreas Seidl has opted to keep a low profile for the time being as he begins his main task of building up the organisation ahead of Audi's arrival.
Alfa Romeo will thus be overseen on race weekends by managing director Alessandro Alunni Bravi, who has been nominated as team representative.
"Bringing a car to life is a long process which touches every department of a racing team, therefore it's a moment of great pride to see it unveiled today," said the Italian.
"We chose to do it in front of our fans, close to our home, because the launch of a new car is not only a moment to state your objectives for the season ahead – it's also a time to give back to the people who have supported you, be it in the grandstands, in front of the TV or back at the factory, and express our gratitude for their passion and their belief in our project.
"Our new car is the results of months of work, but today is just the beginning of a journey. We need to keep working hard, with humility and dedication, to bring performance to the track.
"Everyone in the team is committed to this target and I am confident we will reap the rewards of our work."
The team describes the C43 as an evolution of its predecessor. However, it features substantial changes at the rear, with a new gearbox, rear suspension and cooling layout, with all the changes designed to address weaknesses that were apparent last year.
The other key focus was reliability after the team suffered a series of problems in 2022.
"I am very proud of what we have achieved over these last months, because creating a new car is always a massive effort from the team," said technical director Jan Monchaux.
"This car is an evolution of last year, reflecting the new regulations and introducing major changes in the areas where we found improvements to be needed.
"I hope it's going to be quicker than the successful car we had last year, that's what matters most, and more reliable as well – we have put a lot of effort in this direction.
"Now, it's time to get to the track and see how this car performs. I'm happy to get back to racing and I'm confident there will be much more to come from us soon."
In what the team says is a world first, the C43 will be released for the EA Sports official game F1 2022 even before the real version takes to the track in Barcelona this week.