# Skild AI releases physical self-play post-training results; S1 model learns soccer in simulation and transfers to humanoid robots

- Source: Skild AI
- Published: 2026-09-22T16:00:00.000Z
- RoboHot: https://robohot.news/en/items/st09jk3zx0aqxyvq8rxyo7k1j
- Original: https://www.skild.ai/blogs/physical-self-play

## Summary

Skild AI announced that it post-trained its foundation model S1 through physical self-play, letting the policy play against a recent version of itself with scoring as its sole objective. In NVIDIA Isaac Sim, over 140 years of simulated time, it learned skills such as dribbling past opponents, shielding the ball, and tackling, and these skills were successfully transferred to humanoid robots for matches. The authors believe self-play can break through the capability ceiling of pretrained human data, and the next step will be to extend it to everyday tasks such as collaborative manipulation and city-scale navigation.

## Why it matters

The authors describe using physical self-play to let a foundation model acquire soccer skills in simulation and transfer them to real robots, which lets readers learn about a feasible path for self-play-style post-training.