GPT-5 and Gemini Flash 3 Get Worse, Cost 55% More at 'High Effort'

A new Deep Research Bench study of 22 model configurations shows that for top models, higher 'effort' settings reduce accuracy and increase cost. GPT-5's score dropped from 0.496 to 0.481, while its cost per query jumped 55% from $0.25 to $0.39. Gemini 3 Flash saw a similar 5-point accuracy decline. The finding contradicts the assumption that more computational 'thinking' always yields better results for complex research tasks.