Bottas joined the Silver Arrows from Williams shortly ahead of the current season and hit the ground running, scoring a podium first time out in Australia and following that up with his first Grand Prix victory just three races later in Russia. He won again in Austria, and has also claimed two poles and nine podiums from the 13 races to date, lifting him to third in the championship, just 41 points off team mate and three-time world champion Lewis Hamilton.
"We gave Valtteri a big challenge this year: joining the team at the eleventh hour, stepping up to the forefront of F1 and pairing with the sport’s best driver as his team mate. With that in mind, his results have been probably even more impressive," said Toto Wolff, Head of Mercedes-Benz Motorsport.
"There have been ups and downs – more ups, fewer downs – and some great highlights like his two race wins in Russian and Austria. Overall, the balance of his performances and his upward trajectory made it a no-brainer for us to continue with him into 2018.
"For our team, the bonus factors are the respect and sportsmanship that have grown between our two drivers. The chemistry and dynamic between Valtteri and Lewis work and are what we need to take the fight to our competitors."
Bottas added: "When the team hired me for the 2017 season, they took a leap of faith by putting their trust in my skills. This new contract for 2018 shows that I’ve earned that trust.
"I’m happy to have celebrated my first race wins in a Silver Arrow. However, there’s always room for improvement and I still have not shown my full potential.
"I will continue to work hard on and off the track, to further improve my driving, get even better results and show that putting their trust in me was the right decision.
"As a driver, I’ve been able to learn and grow massively, and we have already enjoyed some really good moments this season that I will never forget.
"I’ve been very impressed by the mentality, commitment and the team spirit this team holds. Partnering Lewis has also been really good, and I’m enjoying the respect we have and the will to push this team forward together.
"I want to thank all the board members, the people at the factories in Brackley and Brixworth as well as the race team and all the fans for their support and trust. It means a lot to me."
Source : https://www.formula1.com/en/latest/headlines/2017/9/f1-bottas-mercedes-2018-extension-contract.html