GPT-5 family (GPT-5.5 / GPT-5.6)
Overview
OpenAI's frontier large-language-model family. GPT-5.5 (April 2026) is the broadly available flagship, built for agentic coding, computer use, and knowledge work. GPT-5.6 - variants Sol, Terra and Luna - is the next generation, opened to the public on July 9, 2026 after an initial government-gated preview.
GPT-5.5 is GA across ChatGPT and the API and became the default ChatGPT model in May 2026. GPT-5.6 'Sol' (flagship), 'Terra' (balanced) and 'Luna' (fast/low-cost) entered a staggered, government-gated preview on June 26, 2026 and became publicly available to all users on July 9, 2026. On July 30, 2026 - three weeks after public launch - OpenAI cut Luna API pricing 80% to $0.20/$1.20 per million input/output tokens (from $1/$6) and Terra pricing 20% to $2/$12 (from $2.50/$15), leaving Sol unchanged at $5/$30, widely read as a response to cheap, capable open-weight Chinese models eroding frontier pricing power.