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OpenAI Opens Limited Preview of Three GPT-5.6 Models

June 28, 2026 at 23:06 EDT

Foundation Models
Policy & Regulation
Security

On June 26, 2026, OpenAI officially announced a limited preview of its new GPT-5.6 series (Sol, Terra, and Luna). The flagship Sol improves on coding, science, and cybersecurity, but it is not yet available in ChatGPT; for now it is offered to roughly 20 trusted partners shared with the US government, via the API and Codex.

June 26, 2026 · OpenAI

GPT-5.6 Arrives as Sun, Earth and Moon

OpenAI opens a limited preview of its GPT-5.6 family — flagship Sol, balanced Terra and fast Luna — calling Sol its most capable and security-hardened model yet, available for now only to trusted partners.

SOL ☀

Top tier — engineering, science, security

TERRA ⊕

Balanced — everyday work

LUNA ☾

Fast, low-cost — high volume

Preview pricing — output cost per million tokens

Column height is proportional to output price. Lower tiers cost a fraction of the flagship.

$30

Sol

$15

Terra

Luna

Sol input: $5 Terra input: $2.50 Luna input: $1

½ cost

Terra matches GPT-5.5 performance at half the price

90%

Discount on cached prompt reads

30 min

Minimum cache lifetime; writes at 1.25× input rate

Why a phased release

OpenAI deferred general availability at the U.S. government's request, weighing cyber risks against broad access. Sol ships with its most robust safety stack yet.

API & Codex only — ChatGPT excluded Approval required per participant Weeks of vulnerability probing Broader availability within weeks

Early praise

Persistent logical reasoning
Accurate tool use
Grasps intent from minimal prompts
Human-like text generation

Criticism

Coding creativity still falls short
Limited preview out of reach for ordinary users
Agent infrastructure may matter more than any single model

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