Do Correctness Probes Transfer? A Cross-Family Study of LLM Hidden States

Evan Duan


Abstract
Linear probes on language-model hidden states can predict output correctness, but it remains unclear whether they capture transferable correctness representations. We study out-of-distribution correctness-probe transfer across seven datasets, four task families, and three open-weight LLMs: Qwen3-8B, Llama-3.1-8B, and Gemma-2-9B, with all findings validated across five random seeds. Within-family transfer is consistently stronger than cross-family transfer (gap 0.075 AUC), with code generation showing the clearest pattern across MBPP-test, MBPP-train, and HumanEval. We further find that probe weight directions are nearly orthogonal across most dataset pairs despite strong predictive transfer, suggesting that probes do not encode a single canonical correctness direction. Comparing probes to logprob confidence baselines, we find probe advantage is concentrated in in-domain and within-family transfer cells. We also identify a layer-selection confound where early-layer shortcuts can appear transferable in-domain but fail cross-source. Overall, correctness probes transfer selectively rather than universally, making them most useful in-domain and within task families.
Anthology ID:
2026.aacl-long.227
Volume:
Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers)
Month:
November
Year:
2026
Address:
Hengqin, China
Editors:
Yue Zhang, Ruifeng Xu, Ayu Purwarianti, Tong Rong, Jun Suzuki
Venues:
AACL | IJCNLP
SIG:
Publisher:
Association for Computational Linguistics
Note:
Pages:
5095–5118
Language:
URL:
https://aclanthology.org/2026.aacl-long.227/
DOI:
Bibkey:
Cite (ACL):
Evan Duan. 2026. Do Correctness Probes Transfer? A Cross-Family Study of LLM Hidden States. In Proceedings of the 15th International Joint Conference on Natural Language Processing and the 5th Conference of the Asia-Pacific Chapter of the Association for Computational Linguistics (Volume 1: Long Papers), pages 5095–5118, Hengqin, China. Association for Computational Linguistics.
Cite (Informal):
Do Correctness Probes Transfer? A Cross-Family Study of LLM Hidden States (Duan, AACL-IJCNLP 2026)
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PDF:
https://aclanthology.org/2026.aacl-long.227.pdf