What the announcement is about is still unknown, but Red Bull is said to be pleased with Honda's progress since its junior team Toro Rosso started using the engines this year.
"The progress Honda has made has been obvious," a source told Salzburger Nachrichten newspaper. "I'm convinced that Honda will overtake Renault in 2019."
What Red Bull does decide could affect Carlos Sainz's future.
The Spaniard is on loan from Red Bull to Renault.
"Red Bull will have to tell Carlos if they want him back or they release him by the end of September," his father Carlos Sainz snr said in Montreal.
"But we do not want to wait that long, as Renault wants to continue working with him."