The clue's in the codename. Prior to its unveiling at the Xbox Reveal event last month, this was known only as Flagship. It's a name that marks the standard-bearer for all Xbox One's launch titles, the one that shows everything the new platform can do. It sets the standard for everybody else, and - in a first for the franchise - it's got to do so the day Xbox One launches. It is, says Turn 10 studio head Alan Hartman, "the hardest thing we've ever done."
Part of that is, of course, a huge collection of cars recreated in never-before-seen detail. You can't show up at a console launch with anything less than photographic realism, and this delivers although probably not in the way you're expecting. The world itself is realistically modelled using laser scans accurate to six millimetres of detail. The score is dynamically generated, and the audio effects are astonishing. But the bit where it really feels like science fiction is the AI. There isn't any.
The drive of your life
Faced with the limitless power of Xbox One's cloud computing, Turn 10 has junked AI entirely and handed things over to a vast, slightly sinister-sounding learning network called Drivatar, which sounds like nothing less than Skynet with a driving licence. It means opponents who aren't pre-programmed, but learn from you and other players. Your Drivatar is a digital version of you, constantly refined from watching every game you play.
"It learns how you attack corners and where you cut. It learns how you use the car's unique traits and technolgy, how you drive in traffic and where you play dirty," explains Turn 10's Dan Greenawalt.
"More importantly, it starts to generalise your traits to similar cars, similar circumstances and similar corners, so it can recreate your behaviour on tracks and in cars you've never played. As you train your Drivatar on more cars and tracks, its generalisation decreases. But this isn't simply about replicating your lap times, this is about how you are fast and how you react to pressure and opponents." It is, claims Greenawalt, the end of AI as we know it.
"We unfortunately use the word AI in this industry to say "opponents." And these will be opponents. But they will not be AI, "clarifies Greenawalt." Drivatar is real, genuine intelligence. It's not scripted, it's learning - it's more like search. It's figuring out "oh, I saw what you did there, I see what you did there, I'm going to learn something new and I'm going to go do it."
It's massive boost in realism, and in more way than one, "instead of just being 10 per cent, 20 pre cent of Xbox One's capability, we can make AI 600 per cent of its capability," says Greenawalt. "Put it in the cloud and free up that 10 per cent or 20 per cent to make the graphics better - on a box that's already more powerful than we worked on before."
Which is where those new visuals come in, with their remarkable level of fidelity. If it wasn't for the screen tearing on the work-in-progress build, you'd have difficulty distinguishing Forza's BMW M5 from reality. The secret, it turns out is dirt.
"Everybody wants perfection, and we delivered that in Forza 4 with Autovista," says art team lead Gabriel Garcia. "But perfection is not authentic. So we introduce telltale signs of the manufacturing process." Paint has a barely perceptible orange-peel finish from where the droplets landed. Brake discs display scratches where the pads grip them. Polished surfaces are actually polished with tiny scratches from buffing. Cars look more realistic than the uncanny valley gloss in previous games.
Added to this the road grime from racing, and the teeniest of details such as bluing on the chrome, all of which contribute to what Greenawalt calls "the story of the car" - the way it reflects your journey. "In Forza 4 we had about 54-60 materials in a car," says Garcia. "In Forza 5 we're up to 1,300 unique materials that can be applied to any car. And we haven't hit the limit." Bathed in the fruits of a new lightning system, it's only the swooping camera that gives away the fact it's not a real car.
Dirty driving
The world itself is rendered in the same level of detail. The setting for the opening race, Prague, was chosen to show off Xbox One's graphical chops, and in a first for the series is based on 1:1 laser scanning of the road itself. The resulting wireframe data is accurate to within six millimetres, and paired with high-definition 360-degree video capture of the track - similar to Google Maps' Street View, only far higher resolution - enables Turn 10 to create a course so detailed you can see moss between paving stones, fog coming off the river, or the paint finish on nearby buildings.
This proces is a key example of how the studio's achieving such obsessive levels of detail without requiring a blank cheque and infinite staff; capturing such detailed reference material makes it easier to model the track, leaving artists free to focus on, well, artistic detail. Like more dirt. "The idea is that we're in the 23rd hour of the 24-hour Le Mans," says content art director Matt Collins. "Every track really feels like its really been raced on: it's telling a story as you go round it. If you've seen the end of those races, there's rubber, there's marbles, it just feels like it's been through a war."
It also has to feel like a race that people are attending and caring about. Still more of Xbox One's graphical horsepower is thrown at creating denser crowds, and still more at a remarkable new audio system that makes it sound like a real crowd, thanks to physics-powered sound mixing that juggles thousands of sounds and music samples simultaneously. The detail lavished on the audio rivals that of the visuals, and - possibly because it's more unexpected - to arguably superior effect. Every significant part of every vehicle has been recorded and mapped against a dizzying range of variables - everything from RPM to distance from you to proximity to the wall - and for every car on the track, rather than just yours as before.
Hollywood calling
Then there's the soundtrack. Or rather, there isn't. Where previous games used up all the hardware for car sounds and had to use licensed tracks for music, Forza 5 has a dynamically generated score. Orchestral strings, pounding drums and choral chants have been separately recorded and are mixed together on the fly. It sounds more like Halo than a racing game, and it builds from the serenity of inspecting your garage to the pending drama of the imminent battle, then - following the purposefully tense quiet of the 3,2,1 build-up - to a stirring cinematic score.
"We're inspired by the Hollywood car chase," says audio director Nick Wiswell. "And we can control elements of the mix based on what's happening in the race. If you're towards the back, we can dim it out; if you're towards the front, we can push it up. We even have an element where, as you hunt down the guy in front, you have a tension layer we can bring in and build. And it releases and starts again as you get to the next guy."
Better yet, the audio team have borrowed from Hollywood to crank up the emotional impact. Tyre screeches have been mixed with human screams; a throaty supercar throttle has been infused with a lion's roar. The result tingles the nervous system in the way a simple engine note never could, and in-game it delivers a knockout blow.
As three cars thunder wheel-to-wheel under an arch and into a square, an awesome combination of duelling engine notes bounces off surrounding buildings, the roar of the crowd and the thumping rotors of a camera helicopter. It's here, with the city stretching off into the seemingly limitless draw distance and the sunlight glaring off the windows, that feels like the next generation is here.
Even now, before we get behind the wheel, it's clear Xbox One is powering a game that's several orders of magnitude more ambitious than any other racing game. It will, quite literally, put you closer to the vehicles and the track than any other game, too. The only thing missing is smell. So far.
