GPT-5.4 Pro is the high-compute sibling of GPT-5.4 for careful, high-stakes assistant work. Our tests show solid helpfulness, instruction following, and comprehension when the ask is dense or unforgiving. Empathy is fine but not standout. Creative writing dips as deeper reasoning favors terse working notes over polished narrative voice—an early version of the tradeoff that becomes sharper in GPT-5.5+. Slower and much more expensive than GPT-5.4; worth it mainly when a single careful answer justifies the cost.