Title: Meta-Reinforcement Learning With Informed Policy Regularization. Abstract: Meta-reinforcement learning aims at finding a policy able to generalize to new environments. When facing a new environment, this policy must explore to identify its particular characteristics and then exploit this information for collecting reward.  We consider the online adaptation setting where the agent needs to trade-off between the two types of behaviour within the same episode. Even though policies based on recurrent neural networks can be used in this setting by training them on multiple environments, they often fail to model this trade-off, or solve it at a very high computational cost. In this paper, we propose a new algorithm that uses privileged information in the form of a task descriptor at train time to improve the learning of recurrent policies.  Our method learns an informed policy (i.e., a policy receiving as input the description of the current task) that is used to both construct task embeddings from the descriptors, and to regularize the training of the recurrent policy through parameters sharing and an auxiliary objective. This approach significantly reduces the learning sample complexity without altering the representational power of RNNs, by focusing on the relevant characteristics of the task, and by exploiting them efficiently.  We evaluate our algorithm in a variety of environments that require sophisticated exploration/exploitation strategies and show that it outperforms vanilla RNNs, Thompson sampling and the task-inference approaches to meta-reinforcement learning.