DeepSeek vs. o3-mini: How Well can Reasoning LLMs Evaluate MT and
  Summarization?
Authors: name: Daniil Larionov, name: Sotaro Takeshita, name: Ran Zhang, name: Yanran Chen, name: Christoph Leiter, name: Zhipin Wang, name: Christian Greisinger, name: Steffen Eger

Reasoning-enabled large language models (LLMs) have recently demonstrated
impressive performance in complex logical and mathematical tasks, yet their
effectiveness in evaluating natural language generation remains unexplored.
This study systematically compares reasoning-based LLMs (DeepSeek-R1 and OpenAI
o3) with their non-reasoning counterparts across machine translation (MT) and
text summarization (TS) evaluation tasks. We evaluate eight models across three
architectural categories, including state-of-the-art reasoning models, their
distilled variants (ranging from 8B to 70B parameters), and equivalent
conventional, non-reasoning LLMs. Our experiments on WMT23 and SummEval
benchmarks reveal that the benefits of reasoning capabilities are highly model
and task-dependent: while OpenAI o3-mini models show consistent performance
improvements with increased reasoning intensity, DeepSeek-R1 underperforms
compared to its non-reasoning variant, with exception to certain aspects of TS
evaluation. Correlation analysis demonstrates that increased reasoning token
usage positively correlates with evaluation quality in o3-mini models.
Furthermore, our results show that distillation of reasoning capabilities
maintains reasonable performance in medium-sized models (32B) but degrades
substantially in smaller variants (8B). This work provides the first
comprehensive assessment of reasoning LLMs for NLG evaluation and offers
insights into their practical use.