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OpenAI Unveils GPT-5.6 in Limited Preview With Sol, Terra and Luna Tiers

June 28, 2026 at 02:24 EDT

Foundation Models
AI Agents

Around June 26, 2026, OpenAI announced a limited preview of its new "GPT-5.6" model family, organized into three tiers named after celestial bodies: the flagship Sol, the balanced work-oriented Terra and the fast, low-cost Luna. For now it is available only through the API and Codex.

June 26, 2026 · OpenAI

GPT-5.6 Arrives as Sol, Terra & Luna — One Generation, Three Tiers

OpenAI splits the "generation" (the number 5.6) from the "tier" (the name): Sol the flagship, Terra the balanced mid-tier, and Luna the fastest and cheapest — each priced per million tokens so users pick by use case and budget.

SOL

Flagship — reasoning, coding, science, security

$5 in / $30 out

TERRA

Balanced — GPT-5.5-level at about half the price

$2.50 in / $15 out

LUNA

Fastest, cheapest — high-volume everyday work

$1 in / $6 out

Output price per 1M tokens — drawn to scale

$30

SOL

$15

TERRA

LUNA

Luna's output costs one-fifth of Sol's — the tiers make the speed–cost–performance trade-off explicit.

91.9

Sol Ultra score on Terminal-Bench 2.1

~80%

Fewer output tokens on ExploitBench

~20

Limited preview partners (API & Codex only)

Predictable prompt caching

1.25×

Cache writes vs. uncached input rate

−90%

Discount on cache reads

Sol also adds a "max" reasoning effort and an "ultra" mode that runs sub-agents in parallel.

Welcomed

Clear tiering seen as practical for developers
Progress on agentic coding and long-running tasks
Sol said to surpass Claude Mythos 5 on some tasks

Questioned

Doubts over Luna's performance
Fairness of limited, partner-only access
Not yet in ChatGPT; general release "within weeks," possibly with country limits

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