The next generation of Infiniti's G series sedan won’t be the only new Japanese premium sedan to make its world premiere at the 2013 North American International Auto Show (NAIAS for short) in Detroit next month, as it will be joined by the all-new 2014 Lexus IS.
As you may have expected, Lexus isn't ready to share pictures and details about the new IS just yet, but it did have this to say about its BMW 3-Series rival:

"Inspired by the acclaimed LF-CC concept and with design cues of the LFA, the new IS has been completely redesigned, inside and out."

Our spy pictures confirm Lexus' claims that the new IS will indeed be closely styled after the LF-CC coupe that was originally displayed at the Paris Motor Show in September before it made its way to North America and the ongoing Los Angeles Auto Show.

As for the LF-CC, from what we've heard, it will form the base for a new IS Coupe model that will follow in the very near future.

What is it?
This is an early prototype of the all-new Lexus IS. The IS isn't being launched until the Detroit show in mid-January so much of the car's detail, including the interior and exterior styling, was under wraps for this drive. The UK will be getting two models: a V6 petrol-powered IS250 (which is mainly for the model's UK private buyers), and the new IS300h driven here, which combines a 2.5-litre, four-cylinder petrol engine with an electric motor and a battery pack.

This latter car is intended to be Lexus’s big breakthrough in the UK’s CO2-driven fleet market. Remarkably, Lexus is aiming to get the IS300h certified at "under 100g/km". The new car is based on the same new rear-drive platform as the recently-launched GS, although the wheelbase has been shortened and the track is also slightly narrower.

Lexus's engineers say the structure is extra-stiff, using 25 metres of adhesive, extra spot welds and a new technique called laser screw welding in its construction. The double-wishbone front suspension set-up gets stiffer anti-roll bars and softer spring rates (to try to improve the ride without sacrificing handling), and the multi-link rear suspension is new. The biggest advance is the redesigned CVT transmission, which finally eliminates the widely disliked mismatch between engine speed and vehicle speed so typical of previous CVT ‘boxes.

The interior styling is close to that of the CT compact hatchback. There are two centre console dials, one for the multimedia system and one for switching the chassis between Eco, Normal, Sport and Sport+ modes.

What is it like?
On the short track course on which we drove it, the IS300h was swift and surprisingly capable, with good brakes and fine stability. However, compared to the agile V6 petrol IS, the hybrid was slower to respond to steering inputs and was less keen on rapid direction changes. The extra weight of the electric motor in the nose and the battery packs in the rear are to blame.

On the road, the IS300h is refined and easygoing. It’s fluid on winding roads and has a decent amount of bite in the steering. The overwhelming sense is of effortless progress with a reasonable dash of driver involvement. It is also impressively swift to switch into EV mode in urban traffic, something other hybrids are reluctant to do. It was hard to be definitive about by the ride, which was excellent on smooth roads but thumped somewhat on broken Los Angeles concrete.

Should I buy one?
If you're fed up with rattling and thrumming four-cylinder premium-car diesel engines (which have generally become less refined since the EU5 regulations), the IS 300h could be a very tempting alternative to the German oil-burners. However, only when we establish the real-world economy and have driven it on European roads, and once the pricing is etablished, will be able to get a definitive answer.

Lexus IS300h

Price: £32,000 (est); 0-62mph: 6.9sec (est); Top speed: 140mph (est); Economy: 73mpg (combined, est); CO2: 99g/km (est); Kerbweight: 1765kg (est); Engine type: 4-cyls, 2499cc, petrol; Power: 240bhp (est); Torque: n/a; Gearbox: CVT

Price: £32,000 (est); 0-62mph: 6.9sec (est); Top speed: 140mph (est); Economy: 73mpg (combined, est); CO2: 99g/km (est); Kerbweight: 1765kg (est); Engine type: 4-cyls, 2499cc, petrol; Power: 240bhp (est); Torque: n/a; Gearbox: CVT

Lexus has fitted seats that are low-set, soft and grippy but there was little else to be gleaned from the camouflaged interior apart from one major point.

Because this IS is longer than the current model by 75mm, and the wheelbase (the distance between front and rear wheels) is 70mm longer, more space has been liberated for knee room in the rear seat.

This particular weakness of the current car has been largely remedied: the door openings are wider, knee room is greatly enhanced (by a whopping 90mm according to Lexus) and there’s even a little more elbow room in the 12mm wider body.