  This paper introduces the offline meta-reinforcement learning (offline
meta-RL) problem setting and proposes an algorithm that performs well in this
setting. Offline meta-RL is analogous to the widely successful supervised
learning strategy of pre-training a model on a large batch of fixed,
pre-collected data (possibly from various tasks) and fine-tuning the model to a
new task with relatively little data. That is, in offline meta-RL, we
meta-train on fixed, pre-collected data from several tasks in order to adapt to
a new task with a very small amount (less than 5 trajectories) of data from the
new task. By nature of being offline, algorithms for offline meta-RL can
utilize the largest possible pool of training data available and eliminate
potentially unsafe or costly data collection during meta-training. This setting
inherits the challenges of offline RL, but it differs significantly because
offline RL does not generally consider a) transfer to new tasks or b) limited
data from the test task, both of which we face in offline meta-RL. Targeting
the offline meta-RL setting, we propose Meta-Actor Critic with Advantage
Weighting (MACAW), an optimization-based meta-learning algorithm that uses
simple, supervised regression objectives for both the inner and outer loop of
meta-training. On offline variants of common meta-RL benchmarks, we empirically
find that this approach enables fully offline meta-reinforcement learning and
achieves notable gains over prior methods.
