What is GPT-5.6 Sol?

GPT-5.6 Sol is OpenAI's flagship AI model as of July 2026 — the most capable tier of the GPT-5.6 family, which reached general availability on July 9, 2026 after a limited preview that began in late June. It sits above two cheaper siblings, Terra and Luna, and is the model you get by default when an API request uses the plain gpt-5.6 alias.

In practical terms, Sol is built for the hardest work.

• complex reasoning
• long agentic coding sessions
• analysis over big documents

It ships with a 1.05-million-token context window, up to 128K tokens of output per response, and selectable reasoning-effort levels, and it runs in ChatGPT (from the Plus plan), Codex, GitHub Copilot, and the API under the model ID gpt-5.6-sol.

Pricing, as of July 2026, is $5 per million input tokens and $30 per million output tokens — the same list price as its predecessor GPT-5.5, which is part of the pitch: newer model, same rate. Teams that don't need frontier-level reasoning usually route everyday work to Terra ($2.50/$15) or Luna ($1/$6) instead and reserve Sol for the requests that genuinely need it.