Title: CaTS-Bench: Can Language Models Describe Numeric Time Series?
Primary area: datasets and benchmarks
Keywords: time series, benchmark, llm

Abstract: Time series captioning, the task of describing numeric time series in natural language, requires numerical reasoning, trend interpretation, and contextual understanding. Existing benchmarks, however, often rely on synthetic data or overly simplistic captions, and typically neglect metadata and visual representations. To close this gap, we introduce **CaTS-Bench**, the first large-scale, real-world benchmark for **C**ontext-**a**ware **T**ime **S**eries captioning. CaTS-Bench is derived from *11* diverse datasets reframed as captioning and Q&A tasks, comprising roughly *465k* training and *105k* test timestamps. Each sample includes a numeric series segment, contextual metadata, a line-chart image, and a caption. A key contribution of this work is the scalable pipeline used to generate reference captions: while most references are produced by an oracle LLM and verified through factual checks, human indistinguishability studies, and diversity analyses, we also provide a human-revisited subset of *579* test captions, refined from LLM outputs to ensure accuracy and human-like style. Beyond captioning, CaTS-Bench offers *460* multiple-choice questions targeting deeper aspects of time series reasoning. We further propose new tailored evaluation metrics and benchmark leading VLMs, highlighting both their strengths and persistent limitations. Together, these contributions establish CaTS-Bench and its captioning pipeline as a reliable and extensible foundation for future research at the intersection of time series analysis and foundation models.

TL;DR: The first multimodal large-scale benchmark for time series captioning and understanding.