@inproceedings{cornelius-etal-2026-cane,
title = "{CANE} is a Format: Rethinking Output Formats for Few-Shot {LLM}-Based Named Entity Recognition",
author = "Cornelius, Joseph and
Ito, Kei K and
Rinaldi, Fabio",
editor = "Lee, Hung-Yi and
Dev, Sunipa and
Li, Jessy and
Elliott, Desmond",
booktitle = "Findings of the {A}ssociation for {C}omputational {L}inguistics: {EMNLP} 2026",
month = oct,
year = "2026",
address = "Budapest, Hungary",
publisher = "Association for Computational Linguistics",
url = "https://aclanthology.org/2026.findings-emnlp.1398/",
doi = "10.18653/2026.findings-emnlp.1398",
pages = "29773--29800",
ISBN = "979-8-89176-462-0",
abstract = "Output format selection is a necessary but understudied dimension of few-shot named entity recognition (NER) with large language models. Existing formats carry characteristic failure modes under autoregressive generation, yet output format has not been systematically evaluated as a primary variable in the few-shot setting across diverse domains and entity structural complexity. We evaluate 21 output formats over 17 datasets across two levels of structural entity complexity, using 9 open-weight models without fine-tuning, ranging from 1.7B to 70B parameters. Output format is the main factor affecting performance, with a 41.7 F1 points difference between the best and worst formats. This exceeds the gains from scaling models parameters within-family. Furthermore, output format accounts for approximately 49.1{\%} of F1 variance on simple datasets and 74.9{\%} on complex ones. We describe three mechanistically distinct failure modes that explain these observed differences; each existing format violates at least one of three properties jointly necessary for robust few-shot NER. We propose CANE (Context-Anchored Natural Expression), a format family addressing all three properties. All CANE variants ranked the highest on simple and complex datasets. This includes the GENIA dataset where all other formats had near-zero scores across nine models, indicating the necessity of the three properties. These findings highlight the importance of output format in few-shot named entity recognition, particularly for annotations involving overlapping or discontinuous entities."
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<abstract>Output format selection is a necessary but understudied dimension of few-shot named entity recognition (NER) with large language models. Existing formats carry characteristic failure modes under autoregressive generation, yet output format has not been systematically evaluated as a primary variable in the few-shot setting across diverse domains and entity structural complexity. We evaluate 21 output formats over 17 datasets across two levels of structural entity complexity, using 9 open-weight models without fine-tuning, ranging from 1.7B to 70B parameters. Output format is the main factor affecting performance, with a 41.7 F1 points difference between the best and worst formats. This exceeds the gains from scaling models parameters within-family. Furthermore, output format accounts for approximately 49.1% of F1 variance on simple datasets and 74.9% on complex ones. We describe three mechanistically distinct failure modes that explain these observed differences; each existing format violates at least one of three properties jointly necessary for robust few-shot NER. We propose CANE (Context-Anchored Natural Expression), a format family addressing all three properties. All CANE variants ranked the highest on simple and complex datasets. This includes the GENIA dataset where all other formats had near-zero scores across nine models, indicating the necessity of the three properties. These findings highlight the importance of output format in few-shot named entity recognition, particularly for annotations involving overlapping or discontinuous entities.</abstract>
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%0 Conference Proceedings
%T CANE is a Format: Rethinking Output Formats for Few-Shot LLM-Based Named Entity Recognition
%A Cornelius, Joseph
%A Ito, Kei K.
%A Rinaldi, Fabio
%Y Lee, Hung-Yi
%Y Dev, Sunipa
%Y Li, Jessy
%Y Elliott, Desmond
%S Findings of the Association for Computational Linguistics: EMNLP 2026
%D 2026
%8 October
%I Association for Computational Linguistics
%C Budapest, Hungary
%@ 979-8-89176-462-0
%F cornelius-etal-2026-cane
%X Output format selection is a necessary but understudied dimension of few-shot named entity recognition (NER) with large language models. Existing formats carry characteristic failure modes under autoregressive generation, yet output format has not been systematically evaluated as a primary variable in the few-shot setting across diverse domains and entity structural complexity. We evaluate 21 output formats over 17 datasets across two levels of structural entity complexity, using 9 open-weight models without fine-tuning, ranging from 1.7B to 70B parameters. Output format is the main factor affecting performance, with a 41.7 F1 points difference between the best and worst formats. This exceeds the gains from scaling models parameters within-family. Furthermore, output format accounts for approximately 49.1% of F1 variance on simple datasets and 74.9% on complex ones. We describe three mechanistically distinct failure modes that explain these observed differences; each existing format violates at least one of three properties jointly necessary for robust few-shot NER. We propose CANE (Context-Anchored Natural Expression), a format family addressing all three properties. All CANE variants ranked the highest on simple and complex datasets. This includes the GENIA dataset where all other formats had near-zero scores across nine models, indicating the necessity of the three properties. These findings highlight the importance of output format in few-shot named entity recognition, particularly for annotations involving overlapping or discontinuous entities.
%R 10.18653/2026.findings-emnlp.1398
%U https://aclanthology.org/2026.findings-emnlp.1398/
%U https://doi.org/10.18653/2026.findings-emnlp.1398
%P 29773-29800
Markdown (Informal)
[CANE is a Format: Rethinking Output Formats for Few-Shot LLM-Based Named Entity Recognition](https://aclanthology.org/2026.findings-emnlp.1398/) (Cornelius et al., Findings 2026)
ACL