GPT-5.6 Terra sits between the budget Luna and the flagship Sol in OpenAI's mid-2026 line. All three share the same 1.05-million-token context window, the same 128,000-token output ceiling and the same February 2026 knowledge cutoff, so the tiers are separated by capability and price rather than by shape.
Terra is priced at $2 per million input tokens against Sol's $5, which OpenAI positions as roughly half the cost of the previous GPT-5.5 generation. On the Artificial Analysis Coding Agent Index it lands just above Claude Fable 5 - short of Sol, but close enough that Terra is the tier most API work will land on when the flagship is not worth its bill.