Portuguese da Costa, 22, was the hot favorite all season to move into the energy drink company's second formula one team next year.
But, with Daniel Ricciardo moving to Red Bull, the F1 paddock was surprised to learn that 19-year-old GP3 driver Daniil Kvyat ultimately got his job.
Is it because Russian Kvyat – although arguably the most impressive compared to fellow Red Bull juniors da Costa and Carlos Sainz Jr – is bringing sponsor backing to the seat?
Dr Helmut Marko, the Red Bull driver supremo, insists "performance" was the only criteria.
He did admit to Germany's Auto Motor und Sport, however, that "two Russian companies have already contacted us".
"Kvyat provides us with the best overall package," the Austrian insisted.
"He has proved that he can handle the pressure, which is something we missed in da Costa.
"If he is already faltering in the junior categories, how will it be in formula one?" Marko asked rhetorically.
"I can't tell you how many drivers were sold as a huge talent before they failed at the very top. But Kvyat's curve has been all uphill.
"Da Costa's was flat, or it went down."
Coming from Marko's blunt mouth, that sounds like the death knell for da Costa, in the wake of a long line of Red Bull juniors who didn't make the grade and were ruthlessly dropped.
But Marko insists: "We have not executed da Costa; he is staying in our family. Now we have to think about his future program.
"First of all, he remains the simulator and reserve driver for Red Bull Racing," he revealed.
Marko also stamped out speculation the McLaren-groomed Stoffel Vandoorne was considered by Red Bull for Ricciardo's seat.
"I have never spoken with Herr Vandoorne," he insisted. "There was no offer — I don't even know what he looks like."