ReverseEOL: Improving Training-free Text Embeddings via Text Reversal in Decoder-only LLMs

Ailiang Lin, Zhuoyun Li, Yusong Wang, Keyu Mao, Kotaro Funakoshi, Manabu Okumura


Abstract
Recent advances in Large Language Models (LLMs) have opened new avenues for generating training-free text embeddings. However, the causal attention in decoder-only LLMs prevents earlier tokens from attending to future context, leading to biased contextualized representations. In this work, we propose Reverse prompting with Explicit One-word Limitation (ReverseEOL), a simple yet effective method for enhancing the representational capability of frozen LLMs. ReverseEOL augments the standard forward embedding with an additional reversed embedding derived from the reversed input text. Since reversing the input exposes each token to context inaccessible in the original order, the resulting reversed embedding effectively provides complementary information to the original one. As a result, combining the forward and reversed embeddings yields a richer final representation. Comprehensive experiments on STS and MTEB benchmarks demonstrate that ReverseEOL significantly improves the performance of existing training-free baselines across a broad range of LLMs with diverse architectures and scales. Extensive ablations and analyses further confirm the necessity of our reversal mechanism. Code is available at [https://github.com/TianBaoGe/ReverseEOL](https://github.com/TianBaoGe/ReverseEOL).
Anthology ID:
2026.emnlp-main.957
Volume:
Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
EMNLP
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
22077–22096
Language:
URL:
https://aclanthology.org/2026.emnlp-main.957/
DOI:
Bibkey:
Cite (ACL):
Ailiang Lin, Zhuoyun Li, Yusong Wang, Keyu Mao, Kotaro Funakoshi, and Manabu Okumura. 2026. ReverseEOL: Improving Training-free Text Embeddings via Text Reversal in Decoder-only LLMs. In Proceedings of the 2026 Conference on Empirical Methods in Natural Language Processing, pages 22077–22096, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
ReverseEOL: Improving Training-free Text Embeddings via Text Reversal in Decoder-only LLMs (Lin et al., EMNLP 2026)
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PDF:
https://aclanthology.org/2026.emnlp-main.957.pdf