Honda has signed a deal to continue as an engine supplier in IndyCar until at least the end of 2017.
The deal includes options for each of the following three seasons, 2018-2020, which will be taken up dependent on the direction IndyCar takes on engine requirements or if additional manufacturers are pursued by the series.
Although the deal was agreed in principle last April, it has taken until now to sort the fine details of the contract.
"It's a two-year agreement with Honda, having an option for three years beyond that," said IndyCar CEO Mark Miles.
"The understanding about that is it's really important for the IndyCar Series and for Honda to know what's next in terms of future development of engines and cars, which we think we'll have a lot of clarity on within that first year or two years of the extension."
Honda struggled compared to sole manufacturer rival Chevrolet in 2015, the first season in which aero kit competition was also allowed.
It was given permission to make changes to its package on all tracks except the superspeedways, and is allowed to make further modifications ahead of the 2016 season.
HPD president Art St Cyr is confident it will make a step forward this year thanks to the redevelopment.
"Part of the whole process, and we knew even going in with the aero kits, is there was a possibility of an imbalance," said St Cyr.
"So last year was a bit of a struggle for us.
"In the rules process, it allows us a chance to redevelop and re-homologate some areas.
"We did have a list of requests that we submitted to IndyCar. They didn't approve all of them.
"Our expectation is that we can be competitive this year.
"One of the things with this package that we have right now is that we have taken the development, design development of this aero kit, from outside Honda to inside Honda.
"Our car will look very similar to our old Formula 1 cars in Honda. A lot of the features are similar."