The Australian became only the second driver to commit to a team for that season after Max Verstappen, whose arrangement with Red Bull runs to 2028.
For all other drivers on the current grid their deals end in 2024 or 2025, and thus 2026 is a blank page for them.
The significance is that the '26 season will see a major chassis rules package introduced, and more importantly, a new power unit formula. And that inevitably triggers memories of 2014, the last time F1 had a big change.
On that occasion, Mercedes got a huge jump on rivals Ferrari and Renault, achieving an advantage that lasted for several seasons.
And when newcomer Honda came a year late in 2015, having had to start an F1 programme from scratch, its dire initial performance showed just how hard it was to get it right.
This time around the change is perhaps not as huge as that from V8s to the hybrid V6, but nor is it insignificant.
In theory, Honda, Ferrari, Mercedes and Renault have a head start thanks to the knowledge they've gained over the past decade, while for newcomers Audi and Red Bull/Ford, the task is more daunting.
At this stage, no one has any idea about how the six power units will compare when they sit on the grid for the first race under the new rules in March 2026.
All each manufacturer knows is where they currently are on their own development curves, while hearing the occasional bit of paddock gossip about so-and-so being well behind - or ahead - on theirs.
Drivers and their managers are left second-guessing how their current teams are likely to perform in 2026, and they know even less about where rivals are likely to be.
What everyone wants to do is repeat the sort of inspired call that Lewis Hamilton made in September 2012 when he shocked the F1 paddock by leaving McLaren and signing for Mercedes, a team which had finished fourth in the previous two seasons and was only fifth that year.
However, the 2014 hybrid regs were looming, and Mercedes bosses Ross Brawn and Niki Lauda convinced Hamilton that Mercedes was well ahead with its project, and would be the place to be.
Having been persuaded, Hamilton had to tread water in the last year of V8s in 2013. The season was dominated by Red Bull, but perhaps even to his surprise the Brackley team made good progress even with the old engine and finished second in the world championship.
His decision to join Mercedes was all about the hybrid and the longer term, and it paid off spectacularly when the team completely dominated the 2014 season. He won the first of what would be six world championships with the Brixworth V6.
Hamilton's Mercedes move stands as an ideal case study as all drivers start to think about whether they want to stay where they are or take a punt on greener pastures elsewhere.
The most intriguing aspect is that the sport's current pacesetter Verstappen has already made a commitment, back in the days when the Red Bull engine project wasn't much more than an idea.
Verstappen has made his call, but he's well aware that his rivals have to keep a close eye on the engine situation.
"I guess that's also part of F1, isn't it?" he says. "Sometimes it's a bit harder to make up your mind. I'm lucky that I grew up in the Red Bull family, and I think we have been growing together again because when I joined it was that period of trying to rebuild after of course, the great championship years.
"And then we got back into the championship-winning ways. And in a way, of course, I've been lucky to be a part of that."
His team boss Christian Horner admits that it's currently guesswork even for the team.
"There's no crystal ball for 2026," he says. "Who knows who's going to be competitive? There's going to be completely new chassis regulations, and a completely new aerodynamic philosophy, so the chassis is going to play a key role.
"The engine is going to play a key role with the split between electrification and combustion, and fuel is going to play a key role in that as well. And so for us, starting from scratch, it's our biggest risk, and it's our biggest opportunity.
"So it's going to be an interesting journey, and I'm sure all the engine manufacturers are working incredibly hard.
"We've got new manufacturers coming in, and Audi as well. But it is a significantly different challenge to the current set of PU regulations."
One of the most intriguing 2026 packages is that at Aston Martin, which will have Hondas as a works partner.
Will the Japanese manufacturer maintain its form as the current pacesetter into the new rules set, or will it get off to a slow start once again?
Aston team principal Mike Krack admits that Honda is already part of discussions with potential drivers as the team considers its options.
"I think these days just opening a wallet of money is not any more an argument," he says. "It is an argument definitely, but the drivers these days, and especially their management, they're asking many more questions than this.
"I think the power unit is playing a substantial role, but I think also the track record, and also I think the current status is always playing a role and is factored in.
"So I think the whole convincing bit is much more difficult, because there are only a few top drivers, or the drivers that everybody wants to have, and you have to have a proper set of presentations and arguments ready to convince them."
Alpine's interim boss Bruno Famin is adamant that the 2026 engine has priority over participating in the driver market chess game.
"I think we are very happy with our drivers, and this is not our first concern," says the Frenchman. "Our first concern is to extract the best possible from the team, the best possible performance, and to develop the best possible power unit.
"I'm talking about the power unit for 2026. The goal is to develop the best possible power unit. One thing after the other. We are happy with the drivers we have now, and let's build a good package."
Drivers tend to have their focus on the next race, but those with contracts running out at the end of next season are already thinking about where they want to be in 2025, ahead of the new regulations.
"I think as drivers it's very difficult to know exactly where every team is at," says Ferrari star Charles Leclerc, who will be one of the key players in the market.
"Obviously, focusing on myself and with Ferrari, I didn't have the chance yet to drive it on the simulator, and as soon as it will be the case, then I'll be able to tell probably a bit more.
"But yeah, for now, it's very difficult to have a clear picture of who is ahead in terms of development."
One of the biggest question marks surrounds Audi. Driving for a big manufacturer has obvious appeal, even to the sport's biggest names, but at what level will its first shot at an F1 engine be at in 2026? And can the Sauber team raise its overall game?
"I heard Audi is going to be pretty strong in '26, that's the rumour!," smiles incumbent Valtteri Bottas. "But of course, like everyone, there's so many question marks. I haven't done any simulator testing either with the latest numbers, so it's still a bit far away.
"But in the end, it will come quick, and at least for Sauber, there's a clear plan what's happening, and there's been lots of work done already for sure."
Perhaps the most interesting aspect of Piastri's extension into 2026 is that he committed to McLaren even though we don't even know what engine the team will be using that season, or at least it hasn't been confirmed in public.
Mercedes is obviously the default setting, as it is for Williams. In theory, both Brixworth customer teams can look elsewhere, and thus to some degree, they are in a similar position to the drivers in trying to evaluate their options.
McLaren's friendly relationship with Toyota has also teed up the intriguing prospect of the Japanese manufacturer returning to the sport at some point beyond 2026.
So what of Hamilton, the man who made that great call back in 2012, and who has just committed to Mercedes for the two interim seasons with the current engine?
"Don't really know much about it to be honest," he says of 2026. "But of course in the not-too-distant future, I'll be looking at my contract to 2030."
