Reasoning models (OpenAI's o-series, DeepSeek-R1) on long prompts use the most, at 15 to 33 Wh per query, up to 100 times more than a small model, because they generate a long internal monologue of thinking tokens before answering. Small models and short queries use the least, whatever the brand.
Read the source article: Which AI uses the least energy? ChatGPT vs Claude vs Gemini