The Energy Cost of Reasoning: Analyzing Energy Usage in LLMs with Test-time Compute

Scaling large language models (LLMs) has driven significant advancements, yet it faces diminishing returns and escalating energy demands. This work introduces test-time compute (TTC)-allocating additional computational resources during inference-as a compelling complement to conventional scaling strategies. Specifically, we investigate whether employing TTC can achieve superior accuracy-energy trade-offs compared to simply increasing model size. Our empirical analysis reveals that TTC surpasses traditional model scaling in accuracy/energy efficiency, with notable gains in tasks demanding complex reasoning rather than mere factual recall. Further, we identify a critical interaction between TTC performance and output sequence length, demonstrating that strategically adjusting compute resources at inference time according to query complexity can substantially enhance efficiency. Our findings advocate for TTC as a promising direction, enabling more sustainable, accurate, and adaptable deployment of future language models without incurring additional pretraining costs.

@article{jin2025_2505.14733,
  title={ The Energy Cost of Reasoning: Analyzing Energy Usage in LLMs with Test-time Compute },
  author={ Yunho Jin and Gu-Yeon Wei and David Brooks },
  journal={arXiv preprint arXiv:2505.14733},
  year={ 2025 }
}