Christian Horner says continued doubts about the costs of producing engines for use in Formula 1 prompted Honda to only commit another year as Red Bull's supplier.
Red Bull motorsport advisor Dr Helmut Marko has previously suggested that the team would pull out of F1 if Honda did likewise, but the partnership will continue into the first year of Liberty Media's new regulations in 2021.
Liberty's attempts to revamp engine regulations, as well as other areas, was met with stiff resistance from Mercedes and Ferrari, meaning power units will be largely unchanged in the new era of F1.
An Horner says Honda remains uncertain how it will be able to afford a long-term commitment to the sport.
"First of all, it's great news they've committed beyond 2020," Horner told Sky Sports. "So we've got a minimum of two years that we're absolutely fixed on.
"They are just waiting to see what are the regulations that are going to come in for either '21 or primarily '22 in regards to homologation or engine freezes to get the costs down.
"These engines are enormously expensive and, [due to] the technology involved, all the manufacturers together want to see some cost reduction in that area.
"Of course, we were taking about the future, the discussion just wasn't about '21.
"There is a real appetite there to build on what we've achieved so far in this relationship.
"It's a great partnership between Red Bull and Honda, as we've seen this year. The key aspect moving forward is absolute clarity on those rules."
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