We started OpenAI Five in order to work on a problem that felt outside of the reach of existing deep reinforcement learningA algorithms. We hoped that by working on a problem that was unsolvable by current methods, we’d need to make a big increase in the capability of our tools. We were expecting to need sophisticated algorithmic ideas, such as hierarchical reinforcement learning, but we were surprised by what we found: the fundamental improvement we needed for this problem was scale. Achieving and utilizing that scale wasn’t easy and was the bulk of our research effort!

To build OpenAI Five, we created a system called Rapid⁠ which let us run PPO⁠ at previously unprecedented scale⁠. The results exceeded our wildest expectations, and we produced a world-class Dota bot without hitting any fundamental performance limits.

The surprising power of today’s RL algorithms comes at the cost of massive amounts of experience, which can be impractical outside of a game or simulated environment. This limitation may not be as bad as sounds—for example, we used Rapid to control a robotic hand⁠ to dexterously reorient a block, trained entirely in simulation and executed on a physical robot. But we think decreasing the amount of experience is a next challenge for RL.

We are retiring OpenAI Five as a competitor today, but progress made and technology developed will continue to drive our future work. This isn’t the end of our Dota work—we think that Dota is a much more intrinsically interesting and difficult (and now well-understood!) environment for RL development than the standard ones used today.

OpenAI Five’s victories on Saturday, as compared to its losses at The International 2018, are due to a major change: 8x more training compute. In many previous phases of the project, we’d drive further progress by increasing our training scale. But after The International, we’d already dedicated the vast majority of our project’s compute to training a single OpenAI Five model. So we increased the scale of compute in the only way available to us: training for longer.