Treasure Hunt: Real-time Targeting of the Long Tail using Training-Time
  Markers
Authors: name: Daniel D'souza; name: Julia Kreutzer; name: Adrien Morisot; name: Ahmet Üstün; name: Sara Hooker
Published: 2025-06-17 16:40:42

Abstract: One of the most profound challenges of modern machine learning is performing
well on the long-tail of rare and underrepresented features. Large
general-purpose models are trained for many tasks, but work best on
high-frequency use cases. After training, it is hard to adapt a model to
perform well on specific use cases underrepresented in the training corpus.
Relying on prompt engineering or few-shot examples to maximize the output
quality on a particular test case can be frustrating, as models can be highly
sensitive to small changes, react in unpredicted ways or rely on a fixed system
prompt for maintaining performance. In this work, we ask: "Can we optimize our
training protocols to both improve controllability and performance on
underrepresented use cases at inference time?" We revisit the divide between
training and inference techniques to improve long-tail performance while
providing users with a set of control levers the model is trained to be
responsive to. We create a detailed taxonomy of data characteristics and task
provenance to explicitly control generation attributes and implicitly condition
generations at inference time. We fine-tune a base model to infer these markers
automatically, which makes them optional at inference time. This principled and
flexible approach yields pronounced improvements in performance, especially on
examples from the long tail of the training distribution. While we observe an
average lift of 5.7% win rates in open-ended generation quality with our
markers, we see over 9.1% gains in underrepresented domains. We also observe
relative lifts of up to 14.1% on underrepresented tasks like CodeRepair and
absolute improvements of 35.3% on length instruction following evaluations.