Daniel Ricciardo and Jean-Eric Vergne have both retained their seats at the Italian squad in what Red Bull's Christian Horner suggested could be a crucial year for their future hopes.
Tost however believes both drivers delivered some 'superb performances' over the 2012 Formula 1 campaign, and that the pressure to improve in the constructors' championship falls more heavily on the team itself.
"The onus to improve is on us," Tost told AUTOSPORT. "Daniel and Jean-Eric are both highly skilled, and they improved throughout 2012.
"OK they have the pressure of having more experience, but both have showed good performance already. It's up to us to provide them with a good car."
Ricciardo, who finished directly behind Vergne in 18th position last year, played down the implied threat of fellow Red Bull protege Antonio Felix da Costa, who tested for Red Bull in last year's young driver test.
"I see a very bright future for him - he has tested the Red Bull car and he's followed a similar path to me and Jean-Eric, and look where we are," Ricciardo said of da Costa.
"I'm sure Portugal can get excited about seeing him in F1 in a few years' time, but he's not a threat to me - he's motivation.
"It's the same as trying to secure sixth, which I believe is realistic. Myself and Jean-Eric have been retained, we will keep improving and hopefully the car will too.
"We have already got a few laps in at Misano and my first impressions were good. I had a smile on my face, which is hopefully telling me I have reasons to be optimistic this year."
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