GPT-6.1 Terra vs. Claude Opus 5.5: Cheaper and faster in three tests at max effort

OpenAI launched GPT-6.1 Terra on October 26, and included two direct comparisons with Opus 5.5 in its marketing materials. It claimed Terra came within five percentage points of Opus 5.5, with fallbacks at less than one-fifth the estimated cost, on Terminal-Bench-Science 0.1, which has agents write code for research tasks such as tracking cell divisions. At max effort, OpenAI describes Terra as more than three times as token-efficient as Opus and one-quarter the price for standard input and output tokens. Separately, it reports an estimated cost per task of about one-ninth. On Agents’ Last Exam, a benchmark of multistep computer-use tasks, Terra scored 60.0% at $1.01 per task, and Opus scored 63.2% at $8.82. That is a 3.2-percentage-point score gap and an 8.73-to-one cost ratio, not identical accuracy.