Researchers injected their simulated environment with changes to gravity, hand angle and other variables so the software learns to operate in a way that is adaptable. That helped narrow the gap between real-world results and simulated ones, which were much better.

The variations helped the hand succeed putting the right letter face up more than a dozen times in a row before dropping the cube. In simulation, the hand typically succeeded 50 times in a row before the test was stopped.

OpenAI's goal is to develop artificial general intelligence, or machines that think and learn like humans, in a way that is safe for people and widely distributed.

Musk has warned that if AI systems are developed only by for-profit companies or powerful governments, they could one day exceed human intelligence and be more dangerous than nuclear wars.

AP