Red Bull have begun negotiations with Honda ahead of a potential switch to the Japanese engine supplier for 2019.
After frustrations in 2017 with Renault, Red Bull had been heavily linked with a change in manufacturer but opted to monitor Honda's progress with sister team Toro Rosso first.
The performances of Pierre Gasly and Brendon Hartley in the opening four races have clearly impressed the Red Bull hierarchy, Toro Rosso moving onto 13 points after Hartley's 10th-place finish in Azerbaijan.
With reports emerging last year that Red Bull and Renault would split at the end of 2018, the four-time world champions have started discussions with Honda ahead of the May 15 deadline to declare their plans for next season.
"Because it was the very first meeting, we discussed the conditions of both sides, what do we expect of each other," Honda motorsport chief Masahi Yamamoto told the official F1 website of talks with Red Bull advisor Helmut Marko.
"It was the first discussion.
"Yes, it was positive. We do believe we were both satisfied. There's a good relationship between us. However, it's the first time we have an official meeting. It's the starting point for a potential future.
"We have the obligation to present the documents on May 15 to the FIA. It's something we are starting to discuss now and it has to be smooth between Honda and Red Bull.
"I want to use the time we have left to discuss with the Honda board members before I take the feedback back to Red Bull to take the next steps.
"When we decided to come back to F1, the plan was not to just stick with one team but work with multiple teams.
"The board members are aware of discussions and there is a big respect for the relationship [with the Red Bull organisation]."
