Attention Overflow: Language Model Input Blur during Long-Context Missing Items Identification

Damien Sileo


Abstract
Large language models (LLMs) can suggest missing elements from items listed in a prompt, which can be used for list completion or similar item recommendation. However, their performance degrades when they are exposed to too many items, as they start to suggest items already included in the input list. This occurs at around 100 items for mid-2024 flagship LLMs. We evaluate this phenomenon on both synthetic problems (e.g., finding missing numbers in a given range of shuffled integers) and realistic movie recommendation scenarios. We refer to this issue as “attention overflow”, as avoiding repetition requires attending to all items simultaneously. Although iterative loops can mitigate this problem, their costs increase with the repetition rate, affecting the language models’ ability to derive novelty from lengthy inputs.
Anthology ID:
2025.findings-ijcnlp.44
Volume:
Proceedings of the 14th International Joint Conference on Natural Language Processing and the 4th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics
Month:
December
Year:
2025
Address:
Mumbai, India
Editors:
Kentaro Inui, Sakriani Sakti, Haofen Wang, Derek F. Wong, Pushpak Bhattacharyya, Biplab Banerjee, Asif Ekbal, Tanmoy Chakraborty, Dhirendra Pratap Singh
Venue:
Findings
SIG:
Publisher:
The Asian Federation of Natural Language Processing and The Association for Computational Linguistics
Note:
Pages:
761–767
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URL:
https://preview.aclanthology.org/ingest-ijcnlp-aacl/2025.findings-ijcnlp.44/
DOI:
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Cite (ACL):
Damien Sileo. 2025. Attention Overflow: Language Model Input Blur during Long-Context Missing Items Identification. In Proceedings of the 14th International Joint Conference on Natural Language Processing and the 4th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics, pages 761–767, Mumbai, India. The Asian Federation of Natural Language Processing and The Association for Computational Linguistics.
Cite (Informal):
Attention Overflow: Language Model Input Blur during Long-Context Missing Items Identification (Sileo, Findings 2025)
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PDF:
https://preview.aclanthology.org/ingest-ijcnlp-aacl/2025.findings-ijcnlp.44.pdf