The English team dominated qualifying ahead of the race, with Brazilian Felipe Massa taking his first pole since 2008, and teammate Valtteri Bottas contributing to a front-row lock-out on Sunday.
In the end, they could not keep up with Mercedes leaders Nico Rosberg and Lewis Hamilton, but everybody else was in their sights, Massa vowed.
"The result today shows that we can compete with the other teams, we can compete with big teams, like Ferrari, like Red Bull," he told journalists after his fourth-place finish.
"But it shows that we are at a good level."
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With Bottas third -- landing his first career podium -- Williams jumped into fifth place in the constructors' standings with 85 points, ahead of McLaren.
Halfway through the season, the team already have more points than in any of the last four years.
"Red Bull are still a bit in front, but Ferrari are 13 points in front of us, Force India are two points in front of us. So it shows that we can put this team definitely in the top level," said Massa.
"I believe we got everything out of today that we could have done."
In the 2013 season, the team managed a mere five points to finish ninth in the table.
"I'm just really thankful for the team. It's been a long long way for us since last year," Bottas said after his podium finish, adding: "That was the best champagne I've ever tasted."
For Massa, this first Austrian Grand Prix in 11 years was crucial not just for the points gained but for the experience Williams will take away from it.