iRacing Season 4 2026 officially arrives on September 15, bringing one of the biggest updates of the year with four new cars, three completely rebuilt tracks, major physics improvements, expanded AI support and several new features.

iRacing has officially unveiled the initial release notes for 2026 Season 4, and the new update promises to significantly expand and improve the simulation. The new season begins on September 15, 2026, at 00:00 UTC, marking the fourth major content and technology release of the year.

Among the biggest highlights are the arrival of the Aston Martin Valkyrie AMR-LMH, two new Caterham race cars, the Gen 4 Grand National, completely rebuilt versions of Road America, Mid-Ohio Sports Car Course and The Milwaukee Mile, as well as a major upgrade to the physics engine designed to improve CPU performance.

Four new cars join iRacing

Season 4 introduces four brand-new vehicles covering several different areas of motorsport.

The most technologically advanced addition is the Aston Martin Valkyrie AMR-LMH, Aston Martin’s Le Mans Hypercar program. The car is powered by a naturally aspirated 6.5-liter V12 producing approximately 670 horsepower and does not use a hybrid system.

Designed with significant involvement from Adrian Newey, the Valkyrie made its competitive debut at the 2025 Qatar 1812 km and subsequently achieved its first IMSA podium at Petit Le Mans.

The car will feature both dry and wet tires and will also be available for AI racing.

Caterham Academy and Caterham 420R

The Caterham lineup expands with two new lightweight racing machines: the Caterham Academy and Caterham 420R.

The Caterham 420R uses a 2.0-liter Ford Duratec engine producing more than 190 horsepower while weighing only around 635 kg. It features a six-speed sequential gearbox, Bilstein racing dampers and Nova Motorsport tires.

The Caterham Academy is designed around a single rain-capable compound suitable for different conditions, while the 420R receives dedicated dry and wet tire specifications.

Both cars are designed to provide a highly physical driving experience, where low weight, momentum conservation and smooth inputs are critical.

Gen 4 Grand National

Another major addition is the Gen 4 Grand National, bringing a classic era of American stock car racing to iRacing.

The car represents the fourth-generation stock cars used from approximately 1992 to 2006, featuring a shorter 105-inch wheelbase and a naturally aspirated 358-cubic-inch V8 producing approximately 600–650 horsepower.

Unlike modern NASCAR cars, the Gen 4 Grand National places a strong emphasis on maintaining momentum and using smooth throttle and steering inputs.

The package also receives a specialized dirt tire for Dirt Oval racing.

Three major tracks rebuilt from the ground up

Season 4 also delivers major improvements to several iconic circuits.

Road America, Mid-Ohio Sports Car Course and The Milwaukee Mile have all received extensive redevelopment work, including new laser scans and updated track artwork.

Road America

Road America has been rebuilt using a new laser scan, allowing iRacing to improve the accuracy of the circuit’s layout and surface.

The updated version is intended to provide a more detailed and authentic representation of the famous Wisconsin road course.

Mid-Ohio Sports Car Course

Mid-Ohio has also been completely rebuilt using a new laser scan.

The updated circuit will be available to existing owners without requiring an additional purchase. All configurations are AI-ready, while the previous version of the track has been retired.

iRacing also noted that pending Hosted Sessions using the old version would be canceled and would not result in additional charges.

The Milwaukee Mile

The historic Milwaukee Mile also receives a major rebuild, bringing the venue up to the latest graphical and technical standards used by iRacing.

The update includes improvements across its available configurations.

Physics engine receives major multithreading upgrade

One of the most important technical changes in Season 4 is not immediately visible on the track.

iRacing has upgraded its physics engine to support greater multithreading through a new system called Physics Islands.

According to the release notes, the change can reduce CPU physics overhead by 50% or more in situations involving heavy traffic, full fields or large AI grids across a wide range of hardware.

This could be particularly important for players running large multiplayer races, endurance events and AI championships.

The improvement should allow the simulation to make better use of modern multi-core processors while potentially reducing CPU-related performance limitations.

Car Rule Sets expanded to 81 vehicles

The new season also expands the Car Rule Sets system to a total of 81 supported vehicles.

In addition, the Global Mazda MX-5 Cup and Sprint Car receive significant mechanical and vehicle-system overhauls.

These changes are intended to improve the behavior and authenticity of the cars while bringing their underlying systems closer to the current simulation standards.

New user interface features

Season 4 introduces several new interface improvements designed to make information easier to access while driving.

Among the new and updated features are:

• Reference Car UI
• Pit Summary widget
• Car Damage widget
• F9 Quick Access
• Minimal/Pinned UI mode
• Fuel Calculator improvements
• Track Map improvements
• Expanded information for selected cars

The new interface tools should make it easier for drivers to monitor race information without constantly navigating through multiple menus.

Full UTF-8 support

Another important quality-of-life improvement is the implementation of full UTF-8 support across several areas of iRacing.

This includes chat messages, display names and filenames used for replays, setups and camera files.

The change should improve compatibility with a wider range of languages and international characters.

Major improvements to the iRacing launcher

The iRacing launcher is also receiving a substantial overhaul.

The Team Registration system has been rebuilt, while the Leagues backend has received a major refresh.

Past race results now have their own pages and can be accessed through deep links, making it easier for drivers and teams to share and revisit historical results.

Another useful addition is the ability to carry Official Session Balance of Performance (BoP) settings into Test Drive sessions.

The launcher also adds Spanish-Mexico as a language option.

Meanwhile, the recently rebuilt Companion App continues to expand the ecosystem surrounding the simulation.

AI racing receives a major expansion

Artificial intelligence is another major focus of Season 4.

iRacing adds AI support for eight additional cars, including:

• Aston Martin Valkyrie AMR-LMH
• Caterham Academy
• Caterham 420R
• Gen 4 Grand National
• Chevrolet Corvette C7 Daytona Prototype
• Formula Renault 2.0
• [Legacy] BMW Z4 GT3
• [Legacy] Riley MkXX Daytona Prototype – 2008

AI support is also being expanded to 19 new track configurations, including Road America, Mid-Ohio, The Milwaukee Mile, Kansas Speedway, Auto Club Speedway, Oswego Dirt and USA International Speedway Dirt.

Several existing vehicles are also receiving specialized AI training, including GT3 cars, GTP, Dallara P217, Global Mazda MX-5 Cup, NASCAR Cup Next Gen on Dirt Oval and Sprint Car.

iRacing has additionally performed focused AI training at circuits such as Circuit of the Americas, Road Atlanta, Sebring International Raceway, Sonoma and Qualcomm Circuit/Naval Base Coronado.

New Start Zones across more than 50 tracks

Season 4 also introduces Start Zones to more than 50 tracks.

The system has been expanded to circuits including Adelaide, Algarve, Mexico City, Imola, Interlagos, Monza, Barber, Brands Hatch, Canadian Tire Motorsport Park, Charlotte Roval, Lédenon, Spa-Francorchamps, Le Mans, Montreal, Navarra, Daytona and Fuji.

The change should improve starting procedures and provide greater consistency across different types of racing.

New multiclass starting system

iRacing is also preparing a new system for multiclass race starts, with dedicated pace cars for each class.

The feature is still subject to a final Week 13 iTested shakedown before being fully deployed. The IMSA iRacing Series is expected to be among the first series to use the new system.

If successful, the change could make multiclass starts more organized and reduce confusion between different vehicle categories.

Gen 4 Grand National package updated

The arrival of the Gen 4 Grand National also changes the structure of its existing content package.

The previous package’s Legacy status has been removed, and it now includes:

• ARCA Menards Chevrolet Impala
• Gen 4 Grand National
• [Legacy] Gen 4 Cup

Existing owners retain access to their content and receive the new Gen 4 Grand National as part of the update.

Pit stop and tire service changes

Season 4 also introduces several changes to pit stop procedures.

For TCR cars, the brake bias valve becomes adjustable in Fixed Setup configurations. A complete four-tire stop takes approximately 40 seconds, with pairs of tires being changed simultaneously.

The NEC fuel service is set to approximately 120 seconds for a full tank.

Legacy GT3 cars also receive updated pit procedures, including the use of two wheel guns and faster tire changes. A pair of tires can be serviced in approximately 10 seconds, while all four tires can be changed in approximately 20 seconds, with specific exceptions such as DTM cars.

These adjustments should have a direct impact on strategy during endurance and long-format races.

Balance of Performance and vehicle updates

Several cars also receive Balance of Performance and mechanical adjustments as part of the Season 4 release.

The release notes include changes to multiple GT and prototype vehicles, covering areas such as fuel consumption, aerodynamic performance, suspension behavior, torque and drag.

The goal is to maintain competitive balance while also addressing vehicle-specific behavior within the simulation.

A major season for iRacing

The 2026 Season 4 update represents a significant combination of new content, technical improvements and quality-of-life features for iRacing.

With four new cars, three completely rebuilt tracks, expanded AI support, a new multithreaded physics architecture and a broad range of interface improvements, the update goes well beyond a traditional content release.

The addition of the Aston Martin Valkyrie AMR-LMH is particularly significant for endurance racing fans, while the Caterham cars offer a completely different lightweight driving experience. Meanwhile, the Gen 4 Grand National adds another historic chapter to iRacing’s growing NASCAR offering.

With Season 4 officially launching on September 15, 2026, players can expect one of the most substantial iRacing updates of the year.