GPT-5.6 Sol

ASSESSMENT

Sol is the flagship of OpenAI's three-tier GPT-5.6 family — Sol, Terra, and Luna — and posts an independent intelligence index of 59, placing it just below the Anthropic pair at the top of the survey. It carries the largest context window in its family at 1.05M tokens and offers an optional Fast mode for latency-sensitive work.

Pricing is where Sol invites scrutiny. At $5 / $30 per million tokens its output rate is the highest in the GPT-5.6 line and among the steepest of any flagship here, and a long-context surcharge applies above 272K input tokens. Against rivals at similar measured capability, Sol is a premium option, and OpenAI appears to be leaning on ecosystem depth — tooling, SDKs, and integrations — as much as price to hold the tier.

For teams already invested in OpenAI's stack, or those who want the family's deepest reasoning with the largest context, Sol is the natural pick. Cost-conscious builders will find Terra a close substitute at a fraction of the output price, and the very top of the independent standings currently belongs to Anthropic.