But Sainz, 23, is merely on 'loan', with Christian Horner insisting that he can be pulled away to Red Bull for 2019 if Daniel Ricciardo decides to leave.
When asked about that, Sainz fended off the question.
"I feel very good at Renault," he told EFE news agency ahead of the Brazilian grand prix.
"They have made me feel at home from day one, helping me to adapt to the team and the car very quickly, in addition to the desire I had to join the team and move forward."
Sainz said that, like Red Bull, Renault is also a F1 "world champion", insisting: "Everything about 2019 and the Red Bull rumours do not interest me right now."
He also defended Renault amid criticism of widespread reliability problems, saying: "They are small problems, and I would not even call them problems.
"They are simply problems with experience, with adaptation of how the car reacts to different situations in the race," said Sainz.