OpenAI halved Terra's input price. There is no dated snapshot to pin.

OpenAI released GPT-6.1 Terra on Monday 26 October 2026. The API charges $1 per million input tokens and $5 per million output, against $2 and $12 for GPT-5.6 Terra; prompts over 272K tokens cost $2 and $7.50. The model page lists a single snapshot, gpt-6.1-terra, and a 1,050,000-token context window.

Same agent traffic, a bill that can fall by more than half on output. But with only the alias to call, you have no dated version to freeze your tests against. Cheap can change shape on you.

Run your eval set against gpt-6.1-terra before you switch, and log the model name on every response. Keep prompts under 272K tokens where you can, since longer ones bill at the higher rate.