  Powerful large language models have facilitated the development of writing
assistants that promise to significantly improve the quality and efficiency of
composition and communication. However, a barrier to effective assistance is
the lack of personalization in LLM outputs to the author's communication style
and specialized knowledge. In this paper, we address this challenge by
proposing PEARL, a retrieval-augmented LLM writing assistant personalized with
a generation-calibrated retriever. Our retriever is trained to select historic
user-authored documents for prompt augmentation, such that they are likely to
best personalize LLM generations for a user request. We propose two key
novelties for training our retriever: 1) A training data selection method that
identifies user requests likely to benefit from personalization and documents
that provide that benefit; and 2) A scale-calibrating KL-divergence objective
that ensures that our retriever closely tracks the benefit of a document for
personalized generation. We demonstrate the effectiveness of PEARL in
generating personalized workplace social media posts and Reddit comments.
Finally, we showcase the potential of a generation-calibrated retriever to
double as a performance predictor and further improve low-quality generations
via LLM chaining.
