A Controllable Examination for Long-Context Language Models
Authors: name: Yijun Yang; name: Zeyu Huang; name: Wenhao Zhu; name: Zihan Qiu; name: Fei Yuan; name: Jeff Z. Pan; name: Ivan Titov
Published: 2025-06-03 14:23:06

Abstract: Existing frameworks for evaluating long-context language models (LCLM) can be
broadly categorized into real-world and synthetic tasks. Despite their utility,
both approaches are accompanied by certain intrinsic limitations. Real-world
tasks are too complex to interpret or characterize and are susceptible to data
contamination. In contrast, synthetic tasks often adopt the
needle-in-the-haystack (NIAH) format, wherein a lack of coherence between the
"needle" and the "haystack" compromises their validity as proxies for realistic
applications. In response to these challenges, we posit that an ideal
long-context evaluation framework should be characterized by three essential
features: seamless context, controllable setting, and
sound evaluation. This study introduces LongBioBench, a
novel benchmark that utilizes artificially generated biographies as a
controlled environment for assessing LCLMs across dimensions of
understanding, reasoning, and trustworthiness.
Our experimental evaluation, which includes 18 LCLMs in total,
demonstrates that most models still exhibit deficiencies in semantic
understanding and elementary reasoning over retrieved results and are less
trustworthy as context length increases. Our further analysis indicates some
design choices employed by existing synthetic benchmarks, such as contextual
non-coherence, numerical needles, and the absence of distractors, rendering
them vulnerable to test the model long-context capabilities. Moreover, we also
reveal that long-context continual pretraining primarily adjusts RoPE embedding
to accommodate extended context lengths. To sum up, compared to previous
synthetic benchmarks, LongBioBench achieves a better trade-off between
mirroring authentic language tasks and maintaining controllability, and is
highly interpretable and configurable.