BudgetThinker: Empowering Budget-aware LLM Reasoning with Control Tokens

Hao Wen, Xinrui Wu, Yi Sun, Feifei Zhang, Liye Chen, Jie Wang, Yifan Su, Yunxin Liu, Ya-Qin Zhang, Yuanchun Li


Abstract
Scaling test-time computation improves the reasoning ability of large language models (LLMs), but the resulting latency and cost limit its use in latency- and cost-sensitive scenarios. We present BudgetThinker, a framework for reasoning-budget adherence that provides online control of chain-of-thought (CoT) length during decoding. Rather than relying on a one-shot prompt instruction, BudgetThinker periodically inserts specialized tokens that communicate the remaining reasoning budget. A two-stage training pipeline, consisting of supervised fine-tuning and curriculum-based reinforcement learning, teaches the model to interpret these signals and adapt its reasoning pace. Across the evaluated 1.5B and 7B text backbones, a 7B multimodal backbone, and a 1.5B code-reasoning model evaluated on HumanEval, BudgetThinker improves budget adherence and accuracy–efficiency trade-offs over competitive baselines. The controlled comparisons isolate the contribution of online ratio signaling from the shared training pipeline. Code is available at https://github.com/MobileLLM/BudgetThinker.
Anthology ID:
2026.findings-emnlp.1465
Volume:
Findings of the Association for Computational Linguistics: EMNLP 2026
Month:
October
Year:
2026
Address:
Budapest, Hungary
Editors:
Hung-Yi Lee, Sunipa Dev, Jessy Li, Desmond Elliott
Venue:
Findings
SIG:
SIGDAT
Publisher:
Association for Computational Linguistics
Note:
Pages:
31182–31205
Language:
URL:
https://aclanthology.org/2026.findings-emnlp.1465/
DOI:
Bibkey:
Cite (ACL):
Hao Wen, Xinrui Wu, Yi Sun, Feifei Zhang, Liye Chen, Jie Wang, Yifan Su, Yunxin Liu, Ya-Qin Zhang, and Yuanchun Li. 2026. BudgetThinker: Empowering Budget-aware LLM Reasoning with Control Tokens. In Findings of the Association for Computational Linguistics: EMNLP 2026, pages 31182–31205, Budapest, Hungary. Association for Computational Linguistics.
Cite (Informal):
BudgetThinker: Empowering Budget-aware LLM Reasoning with Control Tokens (Wen et al., Findings 2026)
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PDF:
https://aclanthology.org/2026.findings-emnlp.1465.pdf