GPT-5.6 shipped July 9, 2026 in three tiers Sol (flagship), Terra (balanced), and Luna (cheapest) all tuned for agentic tool calling.
All three share a 1M-token context window, 128K max output, and native MCP support in the Responses API.
Test any MCP server against Sol, Terra, or Luna in MCP Agent Studio — pick the model, connect a server, and watch each tool call live.
OpenAI dropped GPT-5.6 on July 9, 2026 - and this one is aimed squarely at agents.
Three models landed at once: Sol, Terra, and Luna. Each is built to call tools, not just chat.
