Control Barrier Function for Aligning Large Language Models

arXiv:2511.03121 · cs.CL, cs.AI, cs.SY, eess.SY · Submitted 2025-11-05 · Read on arXiv

cs.CL, cs.AI, cs.SY, eess.SY

Submitted: 2025-11-05

Updated: 2025-11-06

Comments: This work is an extenede version of arXiv:2408.15625 and has been submitted to the IEEE for possible publication

Journal ref: IEEE Transactions on Control Systems Technology 2026

DOI: 10.1109/TCST.2026.3675329

License: http://creativecommons.org/licenses/by-nc-sa/4.0/

The gist: This paper proposes a control-based framework for aligning large language models (LLMs) by leveraging a control barrier function (CBF) to ensure user-desirable text generation.

Terminology

Abstract

This paper proposes a control-based framework for aligning large language models (LLMs) by leveraging a control barrier function (CBF) to ensure user-desirable text generation. The presented framework applies the CBF safety filter to the predicted token generated from the baseline LLM, to intervene in the generated text. The safety filter includes two significant advantages: this safety filter is an add-on type, allowing it to be used for alignment purposes without fine-tuning the baseline LLM, and if there is an evaluation model regarding the desired alignment, it can be directly applied to the filter design. The overall text-generation system is implemented with open-source language models, aiming to generate positive text.

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