Horizon, "Cut to the Knees," Releases HSD V2.1, Teaching Smart Driving to "Back Up"

Going through traffic lights, steering around illegally parked vehicles, and merging onto highways are all things high-level smart driving already does. But on narrow roads, the car runs into an even trickier problem.

An oncoming car approaches, and there is no room to yield on either side; it turns into a small road, and suddenly the way ahead is blocked. Navigation is still pointing forward, but the car already has no way to go.

At this point, smart driving has to do something else. Back up first, and find itself a new path.

Horizon's HSD V2.1 puts "all-scenario reversing" in a prominent position in this upgrade. Why would a company doing high-level smart driving focus on a reverse gear? Once you see how it handles narrow roads, it becomes easy to understand.

Retreat to Advance—Are You an Experienced Driver?

In the official demo, two cars meet on a narrow road. The HSD-controlled car backs up, adjusts its body near a fork in the road, makes space for the encounter, and then continues driving.

Horizon official demo | After being blocked while passing an oncoming car, it reverses, adjusts its body, and then continues driving.

The car still has to complete its original trip. It backs up in order to find space for the forward movement that follows.

Automated parking arranges actions around a selected parking space. Escaping a meeting situation also requires first judging who yields to whom and where to back up, then connecting reversing with continued driving. If the other car moves forward, or someone walks up behind, the vehicle has to adjust its actions according to the road conditions.

When the steering wheel turns, the rear of the car shifts to one side, and the front also swings to the other side. The system has to see clearly the entire area the car sweeps through and know whether the gap in front of it is actually enough.

Reverse gear is only the beginning. The hard part is finding a way for this trip to continue.

Horizon Has Been Breaking Through in This Area for More Than a Year

On January 13, 2025, Horizon publicly demonstrated urban navigation assist with integrated reversing capability. Three-point, five-point, and N-point turns all appeared in the introduction at that time, and the demo scenarios already included narrow roads and dead ends.

If it cannot make the turn in one go, it moves forward a bit, backs up a bit, and readjusts the body. At that time, HSD was already trying to use continuous forward and backward movement to complete tasks that a forward-only trajectory could not achieve.

On January 13, 2025, three-point, five-point, and N-point turns were disclosed, including a dead-end escape demo.

In June 2026, HSD V2.0 upgraded the world model and end-to-end reinforcement learning training system. In September, Horizon gave the answer for V2.1, incorporating all-scenario reversing into mass-production functions, covering situations such as passing oncoming cars, blocked paths ahead, and escaping from a standstill.

When the car cannot complete the task by only moving forward, Horizon lets HSD switch to another way of moving.

Horizon official demo | Forward and backward movement and steering in confined spaces.

Past demos focused on turning around, but now reversing can also create conditions for moving forward. Horizon is expanding the range of capabilities HSD can handle.

"End-to-End Model Direct Trajectory Output" Is Horizon's Solution Path

On Horizon's official website, a specific end-to-end model solution trajectory is disclosed.

The trajectory is how the car plans to move next. HSD uses a one-stage end-to-end system based on Journey 6P, letting the model connect the environment seen by sensors with the vehicle's motion path. On narrow roads, the actions it needs to learn also include backing up and adjusting heading.

Horizon's official website explicitly uses the phrase "end-to-end model direct trajectory output."

The world model helps the system understand and predict environmental changes, while reinforcement learning improves strategies based on action results. Horizon says that V2.1, through this training system, continues to improve spatial understanding, complex decision-making, and continuous control capabilities.

Training objectives, data, and safety validation are set by engineers, and the model learns under these constraints. What Horizon wants to do is let HSD generate an executable forward-and-backward trajectory when moving forward is not possible.

There is also a detail that is easy to overlook. V2.1's trace reversing can connect with parking assist; if an empty parking space is found while reversing, the car can park into it along the way.

Horizon official demo | Trace reversing connected with parking assist.

Besides Horizon, Other Manufacturers Are Also Working Hard to Break Through in This Direction

Tesla's overseas Model Y manual states that after activating FSD, the vehicle shifts into drive or reverse as needed to leave the parking space, and then begins navigation.

In its 2024 official feature description, XPeng introduced trace reversing of up to 100 meters. After the driver activates the function, the vehicle returns along the recorded original path, using the road it has already traveled to solve the exit problem.

Li Auto's VLA parking manual states that the system controls steering and gear shifting to complete parking, and when entering an unfamiliar campus, it can also recognize signs and autonomously enter and exit according to navigation. Huawei has also included "reversing to escape when passing oncoming cars" in its ADS 5 upgrade plan.

Parking out of a space, exiting along the original route, finding a path in a campus, and actively yielding by reversing when passing oncoming cars are all different tasks. What high-level smart driving is striving for is to let the system judge on its own when to retreat and how to retreat, until the trip is completed.

The Final Hurdle: "Mass Production"

The demo car completed the action, but Horizon still has to put it into mass production and deliver it.

Horizon's announced first batch rollout plan lands on iCAR V