Changes from previous version
First Terra-tier release: replaces the old mini/nano naming with a durable balanced tier. Delivers GPT 5.5-class capability at 2x lower API pricing within the GPT 5.6 generation.
Release Summary
OpenAI's balanced GPT 5.6 tier for everyday work: performance competitive with GPT 5.5 at half the API cost ($2.50/M input, $15/M output). Part of the durable Sol/Terra/Luna family where Terra sits between flagship GPT Sol 5.6 and affordable GPT Luna 5.6. Strong improvements on ExploitGym cyber benchmarks as reasoning effort increases. Analogous to Anthropic's balanced frontier lines such as Claude Opus 4.8 and Claude Sonnet 4.6 for cost-performance everyday agentic work, while Sol targets Claude Fable 5 / Mythos 5 territory. Limited preview via API and Codex with general availability planned soon.
Timeline
GPT-5.6 Terra preview begins
OpenAI previews GPT-5.6 Terra as the balanced tier in the Sol/Terra/Luna family, targeting everyday knowledge work at half the cost of the prior GPT-5.5 flagship.