What "new feature" can make joints more stable?

In a recent gameplay video, the Kerbal Space Program team said that “Thanks to a new Unity feature, heavy rockets got way more stable.” (video link here).

Does anyone have any idea what new feature they are talking about? Joint stability has always been such a hard thing to get right!

I asked the same question on the Unity3D subreddit, and I got a great answer:

“I don’t think its a new feature, but in this interview they explain that adjusting the max angular velocity in the physics settings contribute to more stable joints.”