Andretti's bid was given the green light by the FIA on 2 October, but it has still not gone through the second stage of being approved by the F1 organisation and its CEO Stefano Domenicali.
The team has been active in the Toyota wind tunnel in Cologne since October, and has now released the first image of its 2024-spec model, which will eventually transition into a full 2025 test programme should the entry be confirmed early enough.
Despite not yet having that go-ahead, the team has been increasing the headcount at its design base at Silverstone, which will shortly be transferred to a bigger facility close by.
R&D work is also underway at the GM motorsport HQ in Charlotte, where some 50 further people have been seconded to the project alongside the 70 who are working in the UK.
Technical director Nick Chester says that the design team is working flat out on the basis that it will eventually get the green light from F1 for a debut in either 2025 or 2026.
"I think obviously we'd prefer to have the formal entry and a target year for that bit of focus,” he told Autosport. “But I think we were very happy with the process we went through with the FIA.
“It was very rigorous, and we ticked all the boxes. And we're heads down trying to push on to have a competitive car ready for whatever year the entry becomes.
"I think everyone's reasonably confident given the funding, the Andretti name, the tie-up with GM, GM doing their own power unit for '28, that it should happen.
"I think the nice thing is it's a group of people who are completely on the same page and really enjoying growing a new team. And that makes it a lot of fun, and makes it exciting."
Former Renault technical boss Chester insists there’s no specific cut-off date at which point confirmation of an entry will come too late for 2025 and force a postponement of the team’s debut to 2026.
"We don't really have one, just the earlier that we know, the better car we can do,” he said.
"It's really tricky, it's a super tough question. Because you want to have that confirmation of entry and an entry date, so that you can time the recruitment of all of your staff. Obviously, we're still building up, but you would build up even quicker post-entry.
“The cut-off date is a bit more of a compromise in terms of performance. So you can start pushing it later, but you just end up doing a worse car. The longer it drags out, it makes it harder to put a competitive car on the grid.”
The team is testing a 2024 model that will never race in order to develop its processes as a new group of people drawn from different teams, and in some cases straight from university, begins to work together.
"We're effectively trying to develop with a current car and learn lessons with that geometry, and how we derive more performance out of it,” said Chester.
“But also to try and improve our throughput from concept, CFD, tunnel, results viewing back to CFD. So we're trying to improve processes, and develop a ‘24 car."
If the team does eventually switch to a 2026 entry date it will have to focus on the new rules, although like existing teams it won’t be able to do any aero work until 1 January 2025.
"That's a tricky switchover to make,” said Chester. “Obviously with '26 the rules aren't all defined yet. There's a bit a CAD model out there, and there's some intent. But there's not a full set of regulations yet. So that makes it a little tricky to switch over."
