REVIEW 3 major objections 6 minor 1 cited by
"Lost-in-the-Later": Framework for Quantifying Contextual Grounding in Large Language Models
T0 review · 3 major / 6 minor · reviewed 2026-08-06 · deepseek-v4-flash
Pith's one-line read Large language models systematically underuse later parts of their input, a positional bias the authors call 'lost-in-the-later,' which appears even in contexts of only 50 atomic sentences and is worse for reasoning models and…
desk verdict Useful framework and dataset, and the lost-in-the-later pattern is worth taking seriously, but the central measurement rests on NLI judgments that are validated only on synthetic responses, so the effect is conditional pending a human check. read the letter →
The pith
A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.
The reading
What carries the argument
The machinery is CoPE, a sentence-level evaluation framework. It atomizes both the input context and the model's response into minimal 'atomic sentences,' then uses a bidirectional NLI model (mDeBERTa-v3-based INFUSE) with a threshold of t=0.7 to classify each response sentence as contextual knowledge (CK) if it is entailed by the context, or parametric knowledge (PK) otherwise. From these labels it computes the CK score (fraction of response sentences grounded in context) and a context-recall distribution (fraction of sentences recalled from each segment of the context). The MultiWikiAtomic dataset, built by extending WikiAtomic with Spanish and Danish articles, supplies the controlled contexts of 0–50 atomic sentences, and the recall-by-quartile curves are the instrument that exposes the lost-in-the-later bias.
What would settle it
Take a sample of the paper's response sentences across all three languages and all context quartiles, have human annotators (or an independently validated NLI model) decide entailment, and recompute the context-recall curves; if the late-context deficit shrinks to zero or reverses under the alternative judge, the lost-in-the-later effect is an artifact of the mDeBERTa-v3 classifier rather than a genuine property of the models.
Extended reading notes
Core claim
The central discovery is the 'lost-in-the-later' effect: when answering open-ended questions about a supplied context, LLMs incorporate progressively less information from later segments of the context and rely instead on parametric memory, even when the later information is relevant and the context is short. The paper reports that across six models (GPT-4o, Gemini 1.5 Pro, LLaMA 3.2 90B, LLaMA 3.2 3B, GPT-o3, Qwen 3 235B) and three languages, context recall is highest in the first quartile and lowest in the last, with CK usage peaking near 70%; the pattern persists when context sentences are shuffled, ruling out the original document order as the cause. The authors further find that reasoning models and CoT prompting reduce CK further, that parametric content tends to appear at the end of responses, and that higher CK is associated with less hallucination. On the basis of these measurements, they show that a prompt combining strict context-only instruction with balanced-use instruction increases CK by several points and improves factual grounding in multi-document summarization.
Load-bearing premise
The whole measurement chain hinges on the untested assumption that the mDeBERTa-v3 NLI model, at threshold 0.7, correctly decides in English, Spanish, and Danish whether a response sentence is entailed by a context sentence; if that classifier is biased by sentence position or language, the lost-in-the-later curves would be artifacts of the measurement rather than properties of the LLMs.
Editorial extensions
If this is right
- If the lost-in-the-later effect is real, positional bias is not only a long-context problem: even 50-sentence inputs produce declining recall, so short-context applications such as question answering and summarization need explicit recall awareness.
- Reasoning models and chain-of-thought prompting do not cure grounding and can make it worse, so users should not assume that more reasoning steps mean better context adherence.
- A simple CK prompt that forbids outside information and demands balanced use of all context segments raises CK scores and produces more factually grounded summaries with less hallucination.
- CK score and FActScore move together, so measuring contextual grounding gives a practical proxy for hallucination risk across languages.
Reading between the lines
- Beyond the paper: because the recall decline appears even after shuffling context order, the bias likely lives in how pretrained transformers weight earlier input positions rather than in document structure; this could be tested by probing attention patterns or by training small models on position-randomized data.
- Beyond the paper: the same CoPE measurement could be applied to retrieval-augmented generation pipelines, where late-placed retrieved passages may be systematically ignored, and the CK prompt could be adapted as a retrieval-aware generation instruction.
- Beyond the paper: the finding that CoT shortens responses and lowers recall suggests reasoning and grounding compete for a limited output budget; structured reasoning formats that separate reasoning from the final answer might preserve grounding where free-form CoT loses it.
- Beyond the paper: the CK-score/FActScore correlation suggests CoPE could serve as a lightweight, language-agnostic hallucination monitor in production systems where running full factuality checks is too expensive.
Editorial analysis
A structured set of objections, weighed in public.
Referee Report
Summary. The paper introduces CoPE, a framework that classifies each atomic sentence of a model response as contextual knowledge (CK) or parametric knowledge (PK) using a multilingual NLI model, together with a new dataset, MultiWikiAtomic, containing 15,000 atomic sentences in English, Spanish, and Danish. Using this framework, the authors measure CK scores and context recall (CR) for six LLMs and three languages, and report a 'lost-in-the-later' effect: models increasingly underutilize later parts of the context even when the context is only 50 atomic sentences. They further report that reasoning models and chain-of-thought prompting reduce contextual grounding, that PK increases toward the end of responses, that counterfactual contexts lower CK scores, that higher CK is associated with lower hallucination, and that a CK-informed prompt improves grounding in a summarization case study.
Significance. If the central measurement is valid, the paper makes a useful empirical contribution: it provides a reusable multilingual evaluation framework, a new dataset, and evidence that positional bias in context use appears even in short, knowledge-consistent contexts, which would strengthen and extend the 'lost in the middle' literature. The framework is model-agnostic and applicable to closed models, the dataset and code are released, and the threshold-sensitivity ablation in Appendix B is a good-faith robustness check. However, the main empirical claims are only as strong as the NLI-based entailment judgments, and the paper currently validates those judgments only on synthetic responses. The missing validation on real model outputs is a load-bearing weakness, and the CoT comparison is confounded by response format and length.
major comments (3)
- [§2 and Appendix B] The CK/CR measurements rest entirely on mDeBERTa-v3 NLI entailment judgments at threshold t=0.7, but the accuracy evaluation in Appendix B validates the classifier only on synthetically constructed responses (10 CK sentences, 5 unrelated PK sentences) and on alignment with the authors' prior WikiAtomic setup. Actual model responses contain paraphrase, synthesis, cross-sentence inference, and partial entailment, and the NLI model is known to be weaker in Spanish and Danish; the threshold-sensitivity ablation in Appendix B only filters scores within the same classifier and cannot detect a systematic under-detection of entailment for later context sentences. If such a bias exists, the monotonic decline in CR across quartiles in Figures 9-11 would be a measurement artifact rather than evidence for 'lost-in-the-later.' The authors should validate CoPE on human-annotated samples of real responses, stratified by language, model, and context position, and report per-language agreement and error rates.
- [§4.2, §4.3, and Figure 3] The central quantitative claims—CK plateaus near 70%, CR decreases across quartiles, and the effect persists under randomization—are presented as single aggregate curves without confidence intervals, error bars, or significance tests. With per-topic variability and only six models, the '~5%' shift in the randomization test (Section 4.3) should be accompanied by per-model distributions and a paired test; the qualitative stability of the threshold ablation does not supply this. Reporting bootstrap confidence intervals or mixed-effects models would materially strengthen the claim that the effect is structural rather than noise.
- [Section 5 and Appendix J] The CoT comparison is confounded by response format and length. The CoT prompt instructs the model to return a JSON object with separate 'reasoning' and 'answer' fields; if the full generated text is atomized and scored by CoPE, the reasoning portion is counted in the denominator and is likely to be classified as PK, directly lowering CK and recall independently of the model's actual context use. In addition, Table 5 shows CoT responses are roughly one-third to one-half the length of original responses, so the lower recall in Figure 7 may reflect token-budget constraints rather than a grounding deficit. The authors should either score only the extracted answer field, or analyze the full-output and answer-only conditions separately, and should include a length-matched or length-controlled comparison before concluding that CoT degrades contextual grounding.
minor comments (6)
- [Table 2] The table lists 'CoT + CK Prompt' twice with different CK values (73.10 and 75.10 for English); the second row appears to be mislabeled and should be corrected.
- [§2 and Appendix C] The definition of CR_q is underspecified when a segment Q_q contains multiple sentences: the indicator 'I(S_i is entailed by Q_q)' should state whether entailment is checked against each sentence in the segment and aggregated as a maximum, a union, or some other policy.
- [Throughout] The phenomenon is sometimes written as 'lost in the later' (Section 7, Conclusion) and sometimes as 'lost-in-the-later'; the terminology should be made consistent.
- [§5] There is a duplicated word in 'we explore whether whether better prompting strategies' that should be removed.
- [Appendix J] The text refers to 'CoPEval' in the opening sentence, but the framework is called CoPE elsewhere; the name should be unified.
- [Table 4] The header 'Fasle First' is a typo for 'False First'.
Circularity Check
No significant circularity: CoPE's measurements rest on an external NLI model; the only self-referential element is threshold calibration against the authors' prior WikiAtomic setup, which is not load-bearing.
full rationale
The claimed derivation chain is empirical rather than deductive: contexts and responses are atomized, each response atom is labeled CK/PK by mDeBERTa-v3 bidirectional NLI at threshold t=0.7, and context recall (CR) is computed as per-quartile entailment recall. The lost-in-the-later effect is an observed monotonic decline in CR over input quartiles, not a quantity defined in terms of the paper's own fitted parameters. The central measurement is anchored by an externally trained multilingual NLI model, and the threshold is not fitted to the actual target responses. The only self-referential element is Appendix B's threshold calibration: "We selected t = 0.7 because it yielded distributions most aligned with the original evaluation" from Tao et al. (2024), the authors' prior WikiAtomic work. This is a minor self-citation, but it is not load-bearing: the paper reports a threshold-sensitivity ablation showing "shifts were minimal and the main trends held across languages and models," and Section 4.3 adds a randomization control, so the main positional trend is not forced by the particular threshold choice. The skeptic concern that mDeBERTa-v3 may systematically mislabel actual model responses, especially in Danish, is a measurement-validity risk rather than a circularity: no equation in the paper reduces CK or CR to the NLI model's own outputs by construction, and no fitted parameter is renamed as a prediction. PK = 100 - CK is a complementary definition, not a derived result. The CK-prompt evaluation is a prompt-policy comparison rather than a first-principles prediction, so it does not reduce to its own inputs. Overall, there is no significant circularity; the score of 2 reflects only the minor self-referential calibration step, with the substantive findings relying on external measurement and robustness checks.
Assumptions & free parameters
free parameters (1)
- CK-PK entailment threshold t =
0.7
assumptions (4)
- domain assumption A response sentence is either entailed by the input context (CK) or not (PK), and this dichotomy captures contextual grounding.
- domain assumption GPT-4o prompt-based atomization splits context and responses into faithful minimal propositions across English, Spanish, and Danish.
- domain assumption mDeBERTa-v3 multilingual NLI scores approximate semantic entailment for the three languages at threshold 0.7.
- domain assumption FActScore with a multilingual Wikipedia knowledge base and XLM-R tokenizer measures hallucination in Spanish and Danish adequately.
Cite this review
Pith. "Pith review of "Lost-in-the-Later": Framework for Quantifying Contextual Grounding in Large Language Models." pith.science (2026). https://pith.science/paper/3D5G7KVT
@misc{pith2026250705424,
author = {Pith},
title = {Pith review of: "Lost-in-the-Later": Framework for Quantifying Contextual Grounding in Large Language Models},
year = {2026},
howpublished = {\url{https://pith.science/paper/3D5G7KVT}},
note = {Machine review of arXiv:2507.05424}
}
read the original abstract
Large language models are capable of leveraging both contextual and parametric knowledge but how they prioritize and integrate these sources remains underexplored. We introduce CoPE, a novel evaluation framework that systematically measures contextual knowledge (CK) and parametric knowledge (PK) across models and languages. Using our MultiWikiAtomic dataset in English, Spanish, and Danish, we analyze how large language models (LLMs) integrate context, prioritize information, and incorporate PK in open-ended question answering. Our analysis uncovers a phenomenon we call lost-in-the-later, where LLMs tend to overlook or deprioritize information that appears later in a given context, revealing a strong positional bias that affects contextual grounding. We further find that reasoning models, as well as non-reasoning models prompted with chain-of-thought (CoT), use context even less than non-reasoning models without CoT and fail to mitigate the lost-in-the-later effect. CoT prompting, in particular, results in lower recall and shorter responses, leading to degraded contextual grounding. Based on these insights, we design prompt-based methods to effectively leverage input context. A case study applying CoPE to summarization demonstrates that CK-informed prompting improves factual grounding and reduces hallucination.
Figures
Figures from the paper (20 more)
Forward citations
Cited by 1 Pith paper
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Not All Needles Are Found: How Fact Distribution and Don't Make It Up Prompts Shape Retrieval, Reasoning, and Hallucination in Long-Context LLMs
On a new extended needle-in-a-haystack benchmark, explicit anti-hallucination prompts and dispersed fact placement cause some long-context LLMs to over-refuse or collapse in accuracy, while others remain robust.
Reference graph
Works this paper leans on
-
[1]
Jordi Bayarri-Planas, Ashwin Kumar Gururajan, and Dario Garcia-Gasulla. 2024. https://arxiv.org/abs/2409.15127 Boosting healthcare llms through retrieved context . Preprint, arXiv:2409.15127
work page Pith review arXiv 2024
-
[2]
Baolong Bi, Shenghua Liu, Yiwei Wang, Yilong Xu, Junfeng Fang, Lingrui Mei, and Xueqi Cheng. 2025. https://arxiv.org/abs/2503.15888 Parameters vs. context: Fine-grained control of knowledge reliance in language models . Preprint, arXiv:2503.15888
arXiv 2025
-
[3]
Chaoran Chen, Daodao Zhou, Yanfang Ye, Toby Jia jun Li, and Yaxing Yao. 2025. https://arxiv.org/abs/2410.13387 Clear: Towards contextual llm-empowered privacy policy analysis and risk generation for large language model applications . Preprint, arXiv:2410.13387
work page Pith review arXiv 2025
-
[4]
Alexis Conneau, Kartikay Khandelwal, Naman Goyal, Vishrav Chaudhary, Guillaume Wenzek, Francisco Guzmán, Edouard Grave, Myle Ott, Luke Zettlemoyer, and Veselin Stoyanov. 2020. https://arxiv.org/abs/1911.02116 Unsupervised cross-lingual representation learning at scale . Preprint, arXiv:1911.02116
arXiv 2020
-
[5]
Mehrdad Farahani and Richard Johansson. 2024. https://arxiv.org/abs/2410.05162 Deciphering the interplay of parametric and non-parametric memory in retrieval-augmented language models . Preprint, arXiv:2410.05162
work page Pith review arXiv 2024
- [6]
-
[7]
Muhan Gao, TaiMing Lu, Kuai Yu, Adam Byerly, and Daniel Khashabi. 2024. https://doi.org/10.18653/v1/2024.findings-emnlp.447 Insights into LLM long-context failures: When transformers know but don`t tell . In Findings of the Association for Computational Linguistics: EMNLP 2024, pages 7611--7625, Miami, Florida, USA. Association for Computational Linguistics
-
[8]
Yair Gat, Nitay Calderon, Amir Feder, Alexander Chapanin, Amit Sharma, and Roi Reichart. 2023. https://arxiv.org/abs/2310.00603 Faithful explanations of black-box nlp models using llm-generated counterfactuals . Preprint, arXiv:2310.00603
arXiv 2023
Show all 32 references
-
[9]
Reshmi Ghosh, Rahul Seetharaman, Hitesh Wadhwa, Somyaa Aggarwal, Samyadeep Basu, Soundararajan Srinivasan, Wenlong Zhao, Shreyas Chaudhari, and Ehsan Aghazadeh. 2024. https://arxiv.org/abs/2410.00857 Quantifying reliance on external information over parametric knowledge during...
2024 arXiv
-
[10]
Yuxiao Hu, Qian Li, Dongxiao Zhang, Jinyue Yan, and Yuntian Chen. 2025. https://arxiv.org/abs/2501.03747 Context-alignment: Activating and enhancing llm capabilities in time series . Preprint, arXiv:2501.03747
2025
-
[11]
Evgenii Kortukov, Alexander Rubinstein, Elisa Nguyen, and Seong Joon Oh. 2024. https://arxiv.org/abs/2404.16032 Studying large language model behaviors under context-memory conflicts with real documents . Preprint, arXiv:2404.16032
2024 arXiv
-
[12]
Chin-Yew Lin. 2004. Rouge: A package for automatic evaluation of summaries. In Text summarization branches out, pages 74--81
2004
-
[13]
Smith, Sophie Lebrecht, Yejin Choi, Hannaneh Hajishirzi, Ali Farhadi, and Jesse Dodge
Jiacheng Liu, Taylor Blanton, Yanai Elazar, Sewon Min, YenSung Chen, Arnavi Chheda-Kothary, Huy Tran, Byron Bischoff, Eric Marsh, Michael Schmitz, Cassidy Trier, Aaron Sarnat, Jenna James, Jon Borchardt, Bailey Kuehl, Evie Cheng, Karen Farley, Sruthi Sreeram, Taira Anderson, D...
2025 arXiv
-
[14]
Liu, Kevin Lin, John Hewitt, Ashwin Paranjape, Michele Bevilacqua, Fabio Petroni, and Percy Liang
Nelson F. Liu, Kevin Lin, John Hewitt, Ashwin Paranjape, Michele Bevilacqua, Fabio Petroni, and Percy Liang. 2023 a . https://arxiv.org/abs/2307.03172 Lost in the middle: How language models use long contexts . Preprint, arXiv:2307.03172
2023 arXiv
-
[15]
Yang Liu, Dan Iter, Yichong Xu, Shuohang Wang, Ruochen Xu, and Chenguang Zhu. 2023 b . https://arxiv.org/abs/2303.16634 G-eval: Nlg evaluation using gpt-4 with better human alignment . Preprint, arXiv:2303.16634
2023 arXiv
-
[16]
Yi Liu, Lianzhe Huang, Shicheng Li, Sishuo Chen, Hao Zhou, Fandong Meng, Jie Zhou, and Xu Sun. 2023 c . https://arxiv.org/abs/2311.08147 Recall: A benchmark for llms robustness against external counterfactual knowledge . Preprint, arXiv:2311.08147
2023 arXiv
-
[17]
Yinhan Liu, Myle Ott, Naman Goyal, Jingfei Du, Mandar Joshi, Danqi Chen, Omer Levy, Mike Lewis, Luke Zettlemoyer, and Veselin Stoyanov. 2019. https://arxiv.org/abs/1907.11692 Roberta: A robustly optimized bert pretraining approach . Preprint, arXiv:1907.11692
2019 arXiv
-
[18]
Sewon Min, Kalpesh Krishna, Xinxi Lyu, Mike Lewis, Wen tau Yih, Pang Wei Koh, Mohit Iyyer, Luke Zettlemoyer, and Hannaneh Hajishirzi. 2023. https://arxiv.org/abs/2305.14251 Factscore: Fine-grained atomic evaluation of factual precision in long form text generation . Preprint, ...
2023 arXiv
-
[19]
Olubusayo Olabisi, Aaron Hudson, Antonie Jetter, and Ameeta Agrawal. 2022. https://aclanthology.org/2022.coling-1.542/ Analyzing the dialect diversity in multi-document summaries . In Proceedings of the 29th International Conference on Computational Linguistics, pages 6208--62...
2022
-
[20]
Chen, and Shafiq Joty
Mathieu Ravaut, Aixin Sun, Nancy F. Chen, and Shafiq Joty. 2024. https://arxiv.org/abs/2310.10570 On context utilization in summarization with large language models . Preprint, arXiv:2310.10570
2024 arXiv
-
[21]
Kuniaki Saito, Kihyuk Sohn, Chen-Yu Lee, and Yoshitaka Ushiku. 2024. https://arxiv.org/abs/2402.12170 Where is the answer? investigating positional bias in language model knowledge extraction . Preprint, arXiv:2402.12170
2024 arXiv
-
[22]
Zayne Sprague, Fangcong Yin, Juan Diego Rodriguez, Dongwei Jiang, Manya Wadhwa, Prasann Singhal, Xinyu Zhao, Xi Ye, Kyle Mahowald, and Greg Durrett. 2024. To cot or not to cot? chain-of-thought helps mainly on math and symbolic reasoning. arXiv preprint arXiv:2409.12183
2024 arXiv
-
[23]
Jetter, and Ameeta Agrawal
Yufei Tao, Adam Hiatt, Erik Haake, Antonie J. Jetter, and Ameeta Agrawal. 2024. https://arxiv.org/abs/2409.08435 When context leads but parametric memory follows in large language models . Preprint, arXiv:2409.08435
2024 arXiv
-
[24]
Jason Wei, Xuezhi Wang, Dale Schuurmans, Maarten Bosma, Fei Xia, Ed Chi, Quoc V Le, Denny Zhou, et al. 2022. Chain-of-thought prompting elicits reasoning in large language models. Advances in neural information processing systems, 35:24824--24837
2022
-
[25]
Rongwu Xu, Zehan Qi, Zhijiang Guo, Cunxiang Wang, Hongru Wang, Yue Zhang, and Wei Xu. 2024. https://doi.org/10.18653/v1/2024.emnlp-main.486 Knowledge conflicts for LLM s: A survey . In Proceedings of the 2024 Conference on Empirical Methods in Natural Language Processing, page...
2024 doi
-
[26]
An Yang, Anfeng Li, Baosong Yang, Beichen Zhang, Binyuan Hui, Bo Zheng, Bowen Yu, Chang Gao, Chengen Huang, Chenxu Lv, Chujie Zheng, Dayiheng Liu, Fan Zhou, Fei Huang, Feng Hu, Hao Ge, Haoran Wei, Huan Lin, Jialong Tang, Jian Yang, Jianhong Tu, Jianwei Zhang, Jianxin Yang, Jia...
2025 arXiv
-
[27]
Hao Zhang, Yuyang Zhang, Xiaoguang Li, Wenxuan Shi, Haonan Xu, Huanshuo Liu, Yasheng Wang, Lifeng Shang, Qun Liu, Yong Liu, and Ruiming Tang. 2024 a . https://arxiv.org/abs/2405.19010 Evaluating the external and parametric knowledge fusion of large language models . Preprint, ...
2024 arXiv
-
[28]
Huajian Zhang, Yumo Xu, and Laura Perez-Beltrachini. 2024 b . https://aclanthology.org/2024.eacl-long.102/ Fine-grained natural language inference based faithfulness evaluation for diverse summarisation tasks . In Proceedings of the 18th Conference of the European Chapter of t...
2024
-
[29]
Weinberger, and Yoav Artzi
Tianyi Zhang, Varsha Kishore, Felix Wu, Kilian Q. Weinberger, and Yoav Artzi. 2020. https://arxiv.org/abs/1904.09675 Bertscore: Evaluating text generation with bert . Preprint, arXiv:1904.09675
2020 arXiv
-
[30]
Ming Zhong, Da Yin, Tao Yu, Ahmad Zaidi, Mutethia Mutuma, Rahul Jha, Ahmed Hassan Awadallah, Asli Celikyilmaz, Yang Liu, Xipeng Qiu, and Dragomir Radev. 2021. https://arxiv.org/abs/2104.05938 Qmsum: A new benchmark for query-based multi-domain meeting summarization . Preprint,...
2021 arXiv
-
[31]
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Reviewed August 6, 2026 · model on record in the stance chip above.
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