GPT-5.6
OpenAI's flagship model family — Sol, Terra, and Luna — powering the current ChatGPT experience.
Quality
Modality
multimodal
Context
1M tokens
Access
closed
Fabian's Take
"What surprised me about 5.6 is how little I think about the tiers in practice: Sol when the task is hard, Terra and Luna for volume, and the seams barely show. In my stack, Fable does the thinking and 5.6 works through the resulting list, fast and without drama."
GPT-5.6 is OpenAI’s flagship model family, released in July 2026 as three tiers: Sol (the top reasoning model), Terra (the balanced middle), and Luna (the fast, cheap one, now the default for free ChatGPT accounts). All three share the same 1M-token context window and the same platform features; what you pay for is depth.
How the tiers split
Sol is the one to reach for when errors are expensive, the task is ambiguous, or an agent has to stay coherent across many steps. It powers the higher reasoning settings in ChatGPT’s paid plans, with a Sol Pro variant reserved for Pro subscribers. Terra covers the broad middle at a fraction of Sol’s API price. Luna handles quick, high-volume work and made text-only chats effectively unlimited on the free tier.
How it compares
The 5.6 family closed much of the gap that made previous GPT releases feel like the second choice for demanding work. It is fast, dependable, and cheap to run at the Terra and Luna tiers. For deep architectural thinking and the best writing, Anthropic’s Claude family still has the edge — but as an execution engine that churns through real work all day, GPT-5.6 is hard to beat.
The Verdict
Best for: Reliable daily execution work: formatting, summarizing, translating, and multi-step tasks that need to just get done.
Pros
- Very reliable instruction following across long, multi-step tasks
- Three tiers (Sol, Terra, Luna) let you match cost to the job
- Generous usage allowances on the ChatGPT Pro plan
Cons
- Long-context API requests above 272K input tokens cost double
- Writing style can still feel a bit flat next to Claude
Specs
- Pricing Sol: $5/M input, $30/M output · Terra: $2/$12 · Luna: $0.20/$1.20
- Cost Tier premium
- ⚡Speed Tier fast
- License Proprietary
