Sainz's future has been the subject of intense speculation over recent weeks as he bids to finalise a race seat for next year.
He is known to have an offer to join Sauber on a long-term deal that would run through into its transition to become the Audi works team from 2026.
The German manufacturer wants an imminent decision as it has a desire to get its line-up sorted so it can focus on putting other key foundations in place for the long term.
But Sainz has not wanted to rush into a decision, with there being potential opportunities that could open up at Red Bull and Mercedes.
However, those chances there appear to be fading, with Red Bull likely to keep Sergio Perez on a one-year deal and Mercedes edging towards promoting Andrea Kimi Antonelli from F2.
Motorsport.com has learned, however, that Sainz is engaged in talks with Williams about what it can offer as the squad lays out its ambitious targets for the future.
The squad already has Alex Albon under contract, and team principal James Vowles is pushing for infrastructure changes that he hopes can help it advance up the grid.
One of the aces up its sleeves, which could be very attractive to Sainz, is its customer engine deal with Mercedes for 2026 amid speculation that the German manufacturer has delivered some early promise with its new power unit design.
Speaking at last weekend's Imola Grand Prix, Vowles said the team was doing everything to ensure its rate of progress was as fast as possible over the next few years – even if it meant its current performance was not stellar.
"The 2025 car is in the tunnel, it's as simple as that," he said. "And you're doing that to get ahead of yourself in time for actually 2026 and 2027. All the way through my messaging will continue to be the same: it's not that I don't care about these years [before 2026], but I want us to be successful in the future.
"To do that, I've got to make some pretty harsh decisions in order to transform the organisation."
While many have suspected that Sainz would be forced to take the Audi drive because of the Mercedes and Red Bull situation not looking promising, he had hinted in Monaco about the situation actually being different to what people think.
"Behind the scenes I know more," he said. "You have the rumours and everything, but don't worry, I'm not going to let slip anything.
"I'm going to just put all the options on the table and make the right decision. I can just tell you that, once I open my mind up, everything will happen very quickly. It's all about putting everything together that I feel like I need on my next new contract."
