How Sainz's move affects F1's driver market
The Formula 1 engine/driver web involving McLaren, Honda, Toro Rosso and Carlos Sainz Jr will impact the driver market beyond just next season.
He has been loaned to Renault for next season, meaning the Enstone team and Red Bull are keeping their options open for the longer term.
The appeal of Sainz to Renault is obvious: the team gets one of the most promising young drivers in grand prix racing, forming a potent combination with Nico Hulkenberg as the team strives to move up the leaderboard in its third season with full Renault backing.
For 2019, when Renault will potentially be closer to the front and thus attractive to even the top drivers, the team would still have a free seat. Sainz may well stay, but the other possibility is he is recalled by Red Bull to drive for its senior team.
Daniel Ricciardo is out of contract at the end of 2018, while Max Verstappen is understood to have an option in his 2019 deal that allows him to leave Red Bull should it underperform next season. Both have huge appeal to rival teams.
Kimi Raikkonen's deal at Ferrari has only been extended for one season, while Mercedes currently has no drivers signed for 2019 (although in the coming weeks Lewis Hamilton and Valtteri Bottas could both extend their contracts into that season or beyond).
Verstappen is losing patience with Red Bull-Renault, and while Ricciardo also wants a car with which he can win regularly. Both will want to know about the team's future engine plans, as the possibility is there to join Toro Rosso and switch to Honda in 2019.
If either leaves Red Bull, Sainz can slot in.
The likely replacement for Sainz at Toro Rosso next season (and maybe sooner) is Pierre Gasly. Although out of favour for a while, the Frenchman won the GP2 title last year and has done an excellent job in Super Formula in 2017, winning two races in a row.
How it affects Alonso - and others
With the Renault deal now all-but-confirmed, Fernando Alonso can extend his stay at McLaren.
It's understood he hasn't done so yet, and one could surmise that money is a sticking point, as Honda won't be around to pay the sort of salary he's enjoyed for the past three seasons.
McLaren-Renault has obvious appeal, but only if he can be confident that the 2018 car will be as strong as Red Bull's and capable of challenging for podiums.
The likelihood is he will only sign for one season, keeping his options open for 2019 and beyond. But who would go to McLaren in the unlikely event that Alonso decides not to stay in 2018?
McLaren is adamant there is a Plan B. In theory it's too early for rising star Lando Norris, but this team has gambled on rookies before.
One strong candidate who is still available at the moment is Sergio Perez. With the Renault door now closed, the Mexican looks set to extend his Force India deal, but it's not done yet.
His last stay at McLaren didn't work out, but the team and the management has changed since then, and so has Perez, who now has much more experience.
The other potential vacancy is at Williams. While the Grove team is outwardly happy with Felipe Massa, it harbours big ambitions for 2018 and beyond, and is looking for the best possible partner for Lance Stroll - and one who, thanks to the complication of Martini sponsorship, has to be over 25.
Available options are limited. Alonso has been in the frame. Paul di Resta put himself on the radar in Hungary, and Robert Kubica's name has also cropped up.
The problem the Pole faces is that Renault, the team with which he's done all his testing, has opted not to take him - and proving to anyone else that he can still get the job done is not an easy task, given the lack of testing opportunities.
Ferrari is keen to place the F2 star there, but it also has Antonio Giovinazzi on its books.
Right now, there simply aren't enough seats to go around.