Honda is to continue supplying technical support to Red Bull in Formula 1 until the end of 2025.
The Japanese company officially pulled out of F1 last year, but agreed to continue to supply engines and engineering support to Red Bull until the end of 2023.
That agreement has now been extended by a further two years - until the end of the current engine rules.
Honda says the new deal does not contradict its reasons for quitting F1.
A joint statement issued by Honda Racing Corporation (HRC) and Red Bull on Tuesday said: "While Honda's official withdrawal from F1 allowed the company to divert PU (engine) development resources towards meeting the company's future carbon-neutral goals, the ongoing agreement with Red Bull does not involve development, and HRC will be able to continue its collaboration with Red Bull from within its current resources."
Engine development has been outlawed in F1 following the introduction of a freeze at the start of this season, created so that manufacturers were not devoting resources both to existing engines and developing the new ones that will be introduced in 2026.
However, modifications to power-units for reliability reasons can be permitted, with the agreement of governing body the FIA.
Engine manufacturers often find a way to increase performance via these changes.
The original agreement for two years was to allow Red Bull time to build up its own engine department. This process is ongoing, but Honda's longer contract seems to effectively free up Red Bull to focus on developing its 2026 engine without the distraction of maintaining the existing one.
Honda and Red Bull won the drivers' world championship with Max Verstappen last year, albeit in controversial circumstances after the rules were not followed correctly in a late safety-car period at the final race in Abu Dhabi.
This year, Verstappen is well on his way to winning a second title, and Red Bull are comfortably in the lead in the constructors' championship.
Red Bull team principal Christian Horner said: "Red Bull's partnership with Honda has been an incredibly successful one and we are pleased that this will continue until the end of the current era of the FIA's power-unit regulations in 2025."
Red Bull is in negotiations with Porsche to join forces from 2026. The German car company is expected to work with Red Bull as an engine partner, supplying technical expertise to the team's own engine development programme.
Porsche's involvement is not yet confirmed - the company is waiting for the final issuing of the 2026 engine regulations, which are still being negotiated.
The basic outline of the engine has been agreed. It will continue to be a 1.5-litre V6 turbo hybrid, as it has been since but with significant changes over the current engines.
The hybrid system will be simplified via the removal of the complex and expensive MGU-H - the component that recovers and redeploys energy from the turbo - and the hybrid system will create a greater proportion of the overall power output of the engine.
F1 is also developing a synthetic fully sustainable fuel for use in the engines, with the aim of being carbon-neutral in the life cycle of the fuel - it produces only the carbon taken out of the atmosphere to make it.
However, details of the regulations, such as limits on development and cost, are yet to be agreed.