“Every day you go out there and prove your level, and I think this week I did it really well,” said Sabalenka, who did not drop a set in the tournament.
Looking ahead to the Australian Open, she said: “The only thing I know is that I’ll be there, I’ll be fighting.”
Salablenka lost in the Melbourne Park final last year to Madison Keys, having been champion in 2023 and 2024.
“I’ll do my best to go as far as possible,” she added. “And do a little bit better than last year. That’s my focus.”
Kostyuk, who had not won a set in four previous defeats by Sabalenka, settled herself after cancelling out an early break of serve, but lost her serve again in the 10th game as her opponent stepped up her intensity to win the first set.
The 16th seed was aiming for just a second WTA singles title in what was her first final in two years and fourth in total, but her game crumbled under the weight of Sabalenka’s groundstrokes.
One break of serve at the start of the second set proved enough for Sabalenka to see off the world number 26 as Kostyuk fired into the net on her first championship point.
Kostyuk struggled to hold back tears as she spoke to the Brisbane crowd about conditions at home in Ukraine, where officials have been battling to repair heating and water supplies damaged by Russian bombing.
“I want to say a few words about Ukraine,” she said. “I play every day with a pain in my heart. There are thousands of people who are without light and warm water right now. It’s minus 20 degrees outside so it’s very, very painful to live this reality every day.
“It’s very hot in Brisbane so it’s difficult to imagine, you know, but my sister is sleeping under three blankets because of how cold it is at home.”
Sabalenka’s 22nd WTA title is her first since claiming a fourth Grand Slam at the US Open in September.
Meanwhile, Great Britain’s world number two Alfie Hewett needed just 65 minutes to beat Spanish second seed Martin de la Puente 6-1 6-3 in the men’s wheelchair singles final.
But British top seeds Julian Cash and Lloyd Glasspool lost the men’s doubles final 6-3 3-6 10-8 to third seeds Francisco Cabral, of Portugal, and Austrian Lucas Miedler.