GPT-5.6 Sol API 2026: Sol, Terra, Luna, and the CodeFast Guide

GPT-5.6 Sol, Terra, and Luna are in preview. Learn API/Codex access, official pricing, prompt caching, and CodeFast cost strategy.

On June 26, 2026, OpenAI announced the GPT-5.6 series as a new three-tier family: Sol, Terra, and Luna. Sol is the flagship model; Terra is the balanced model for everyday work; and Luna is the fast, affordable member of the family. The naming system is meant to help developers choose across intelligence, speed, and cost instead of defaulting every task to the largest model.

The announcement matters especially for coding-agent users. OpenAI highlights stronger results for Sol across agentic coding, command-line workflows, biology, and cybersecurity evaluations. More importantly, GPT-5.6 introduces a new `max` reasoning effort and an `ultra` mode for Sol that uses subagents. In other words, the story is not just better answers; it is better execution for long-running developer work that uses tools and breaks work into sub-tasks.

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