This updated Bullet Physics release was used for the
"Learning Agile Robotic Locomotion Skills by Imitating Animals" research., led by Jason Peng.
See also https://xbpeng.github.io/projects/Robotic_Imitation/index.html
And a video here:
https://www.youtube.com/watch?v=lKYh6uuCwRY
There is also an example of model-predictive-control (MPC) for quadruped locomotion.
See the repository here:
https://github.com/google-research/motion_imitation
Install PyBullet using: pip3 install pybullet --user --upgrade