On the afternoon of June 24, 2026, at approximately 5:40 PM, I experienced a severe, sudden braking system failure that directly caused a rear-end collision. I was driving my 2023 Porsche Cayenne E-Hybrid on the highway, traveling to a concert scheduled for 7:00 PM. The highway traffic was heavy and slow-moving (stop-and-go). I was cruising at a moderate speed of approximately 40 to 50 mph. The vehicle ahead of me applied its brakes and came to a gradual, normal stop. I was maintaining a very safe following distance of approximately 30 meters (around 100 feet) behind that vehicle. As I perceived the traffic stopping, I immediately attempted to apply my brakes. However, the brake pedal instantly became extremely hard, felt completely locked up like a stone, and was impossible to press down. Despite having ample distance to stop and applying all my body weight and force onto the brake pedal, there was zero brake assistance from the vehicle, and the brakes failed to engage. The onboard Forward Collision Warning and Automatic Emergency Braking also failed to prevent the accident. As a result, I was completely unable to reduce the speed of the car, and my vehicle rolled forward and collided into the rear of the car in front of me. This was entirely a mechanical/electronic safety system failure. The vehicle is currently available for inspection, and I am requesting a full diagnostic download of the EDR and DME data before any repairs are performed.