Title: Scaling Goal-conditioned Reinforcement Learning with Multistep Quasimetric Distances
Primary area: reinforcement learning
Keywords: Goal-conditioned reinforcement learning, quasimetrics, robotics

Abstract: The problem of learning how to reach goals in an environment has been a long-
standing challenge in for AI researchers. Effective goal-conditioned reinforcement
learning (GCRL) methods promise to enable reaching distant goals without task-
specific rewards by stitching together past experiences of different complexity.
Mathematically, there is a duality between the notion of optimal goal-reaching
value functions (the likelihood of success at reaching a goal) and temporal dis-
tances (transit times states). Recent works have exploited this property by learning
quasimetric distance representations that stitch long-horizon behaviors using the in-
ductive bias of their architecture. These methods have shown promise in simulated
benchmarks, reducing value learning to a shortest-path problem. But quasimet-
ric, and more generally, goal-conditioned RL methods still struggle in complex
environments with stochasticity and high-dimensional (visual) observations. There
is a fundamental tension between the local dynamic programming (TD backups,
temporal distances) that enables optimal shortest-path reasoning in theory and the
statistical global MC updates (multistep returns, suboptimal in theory). We show
how these approaches can be integrated into a practical GCRL method that fits a
quasimetric distance using a multistep Monte-Carlo return. We show our method
outperforms existing GCRL methods on long-horizon simulated tasks with up to
4000 steps, even with visual observations. We also demonstrate that our method
can enable stitching in the real-world robotic manipulation domain (Bridge setup).
Our approach is the first end-to-end GCRL method that enables multistep stitching
in this real-world manipulation domain from an unlabeled offline dataset of visual
observations.

TL;DR: Applying multistep value backup in a quasimetric distance architecture can yield surprisingly strong results.