  As large language models (LLMs) are increasingly deployed in user-facing
applications, building trust and maintaining safety by accurately quantifying a
model's confidence in its prediction becomes even more important. However,
finding effective ways to calibrate LLMs - especially when the only interface
to the models is their generated text - remains a challenge. We propose APRICOT
(auxiliary prediction of confidence targets): A method to set confidence
targets and train an additional model that predicts an LLM's confidence based
on its textual input and output alone. This approach has several advantages: It
is conceptually simple, does not require access to the target model beyond its
output, does not interfere with the language generation, and has a multitude of
potential usages, for instance by verbalizing the predicted confidence or
adjusting the given answer based on the confidence. We show how our approach
performs competitively in terms of calibration error for white-box and
black-box LLMs on closed-book question-answering to detect incorrect LLM
answers.
