Jenna Russell, Marzena Karpinska, Destiny Akinode, James Zhou, Katherine Thai, Bradley Emi, Max Spero, Mohit Iyyer. Proceedings of the 64th Annual Meeting of the Association for Computational Linguistics (Volume 1: Long Papers). 2026.

Synthetic long-context LLM benchmarks (e.g., "needle-in-the-haystack") test only surfacelevel retrieval capabilities, but how well can long-context LLMs retrieve, synthesize, and reason over information across book-length inputs?We address this question by creating NOCHA, a dataset of 1,001 minimally different pairs of true and false claims about 67 recentlypublished English fictional books, written by human readers of those books.In contrast to existing long-context benchmarks, our annotators confirm that the largest share of pairs in NOCHA require global reasoning over the entire book to verify.Our experiments show that while human readers easily perform this task, it is enormously challenging for all ten long-context LLMs that we evaluate: no open-weight model performs above random chance (despite their strong performance on synthetic benchmarks), while GPT-4O achieves the highest accuracy at 55.8%.Further analysis reveals that (1) on average, models perform much better on pairs that require only sentence-level retrieval vs. global reasoning; (2) model-generated explanations for their decisions are often inaccurate even for correctly-labeled claims; and (3) models perform substantially worse on speculative fiction books that contain extensive world-building.The methodology proposed in NOCHA allows for the evolution of the benchmark dataset and the easy analysis of future models.TRUE TRUE Niema takes her students out to world's end and tells them that the fog kills anything it touches, a statement backed by her extensive research into the fog.When Niema takes her students out to world's end and tells them that the fog kills anything it touches, she is intentionally lying to them.

Humanities scholars commonly provide evidence for claims that they make about a work of literature (e.g., a novel) in the form of quotations from the work.We collect a large-scale dataset (RELiC) of 78K literary quotations and surrounding critical analysis and use it to formulate the novel task of literary evidence retrieval, in which models are given an excerpt of literary analysis surrounding a masked quotation and asked to retrieve the quoted passage from the set of all passages in the work.Solving this retrieval task requires a deep understanding of complex literary and linguistic phenomena, which proves challenging to methods that overwhelmingly rely on lexical and semantic similarity matching.We implement a RoBERTa-based dense passage retriever for this task that outperforms existing pretrained information retrieval baselines; however, experiments and analysis by human domain experts indicate that there is substantial room for improvement over our dense retriever.

While machine translation evaluation metrics based on string overlap (e.g., BLEU) have their limitations, their computations are transparent: the BLEU score assigned to a particular candidate translation can be traced back to the presence or absence of certain words.The operations of newer learned metrics (e.g., BLEURT, COMET), which leverage pretrained language models to achieve higher correlations with human quality judgments than BLEU, are opaque in comparison.In this paper, we shed light on the behavior of these learned metrics by creating DEMETR, a diagnostic dataset with 31K English examples (translated from 10 source languages) for evaluating the sensitivity of MT evaluation metrics to 35 different linguistic perturbations spanning semantic, syntactic, and morphological error categories.All perturbations were carefully designed to form minimal pairs with the actual translation (i.e., differ in only one aspect).We find that learned metrics perform substantially better than string-based metrics on DEMETR.Additionally, learned metrics differ in their sensitivity to various phenomena (e.g., BERTSCORE is sensitive to untranslated words but relatively insensitive to gender manipulation, while COMET is much more sensitive to word repetition than to aspectual changes).We publicly release DEMETR to spur more informed future development of machine translation evaluation metrics 1 .

Literary translation is a culturally significant task, but it is bottlenecked by the small number of qualified literary translators relative to the many untranslated works published around the world.Machine translation (MT) holds potential to complement the work of human translators by improving both training procedures and their overall efficiency.Literary translation is less constrained than more traditional MT settings since translators must balance meaning equivalence, readability, and critical interpretability in the target language.This property, along with the complex discourse-level context present in literary texts, also makes literary MT more challenging to computationally model and evaluate.To explore this task, we collect a dataset (PAR3) of non-English language novels in the public domain, each aligned at the paragraph level to both human and automatic English translations.Using PAR3, we discover that expert literary translators prefer reference human translations over machinetranslated paragraphs at a rate of 84%, while state-of-the-art automatic MT metrics do not correlate with those preferences.The experts note that MT outputs contain not only mistranslations, but also discourse-disrupting errors and stylistic inconsistencies.To address these problems, we train a post-editing model whose output is preferred over normal MT output at a rate of 69% by experts.We publicly release PAR3 to spur future research into literary MT. 1

While numerous architectures for long-range language models (LRLMs) have recently been proposed, a meaningful evaluation of their discourse-level language understanding capabilities has not yet followed.To this end, we introduce CHAPTERBREAK, a challenge dataset that provides an LRLM with a long segment from a narrative that ends at a chapter boundary and asks it to distinguish the beginning of the ground-truth next chapter from a set of negative segments sampled from the same narrative.A fine-grained human annotation reveals that our dataset contains many complex types of chapter transitions (e.g., parallel narratives, cliffhanger endings) that require processing global context to comprehend.Experiments on CHAPTERBREAK show that existing LRLMs fail to effectively leverage long-range context, substantially underperforming a segment-level model trained directly for this task.We publicly release our CHAPTERBREAK dataset to spur more principled future research into LRLMs. 1

Tree-based phylogenetic networks, which may be roughly defined as leaf-labeled networks built by adding arcs only between the original tree edges, have elegant properties for modeling evolutionary histories. We answer an open question of Francis, Semple, and Steel about the complexity of determining how far a phylogenetic network is from being tree-based, including non-binary phylogenetic networks. We show that finding a phylogenetic tree covering the maximum number of nodes in a phylogenetic network can be computed in polynomial time via an encoding into a minimum-cost flow problem.