📖 TL;DR 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.
Source: [Dev.to](https://dev.to/rupa_tiwari_dd308948d710f/gpt-56-mcp-testing-servers-with-sol-terra-luna-1524)