A mid-season driver change had been expected for the energy drink's secondary team this year, but Jaime Alguersuari and Sebastien Buemi duly upped their game and have kept their places for now.
Red Bull's rising star Daniel Ricciardo therefore made his debut last weekend for the struggling Spanish team HRT, but a full-time place at Toro Rosso is regarded as likely for the 22-year-old Australian next season.
"He can't drive for Toro Rosso (in 2011) because we have two race drivers who are doing a good job," confirmed team boss Tost to redbull.com.
"What our driver pairing will be in 2012, I don't know yet. This will be decided by Red Bull at the end of the season."