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OpenAI Opens Limited Preview of GPT-5.6 Sol, Terra and Luna

June 26, 2026 at 15:41 EDT

Foundation Models
AI Agents
Policy & Regulation

OpenAI announced a limited preview of its new GPT-5.6 model family on June 26, 2026, comprising the flagship "Sol," the everyday-work "Terra," and the fast, low-cost "Luna." Access begins through the API and Codex for a subset of partners.

June 26, 2026 · OpenAI

GPT-5.6 Arrives — Sol, Terra & Luna, but Behind Closed Doors

A next-generation model family built for stronger agentic work launches as a limited preview — offered only to a small set of government-approved partners via API and Codex, with broad availability promised "in the coming weeks."

capability tiers: Sol, Terra, Luna

~91%

Sol Ultra on TerminalBench

Terra: GPT-5.5 performance at half the price

90%

discount retained on cached reads

Three tiers, three price points

Output price per 1M tokens — column height scaled to cost.

$30

Sol

Flagship

$15

Terra

Balanced

Luna

Fast, low-cost

Input per 1M tokens: Sol $5 · Terra $2.50 · Luna $1

Why access is gated

A U.S. government request, prompted by the models' high capabilities in cybersecurity and biology, limited the launch to trusted partners.

No ChatGPT integration during the preview

API & Codex only, for approved partners

OpenAI: this "should not become a long-term default"

Praise

Strong on agentic workloads
Markedly improved output-token efficiency
"Most robust safety stack to date"

Criticism

Government-approval-gated release format
Not aimed at general users yet
Confusing Sol / Terra / Luna naming

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