What Is GPT-5.6 Sol? Terra and Luna Performance and Pricing

What Is GPT-5.6 Sol (the 3 Models)

GPT-5.6 Sol is the most capable model from OpenAI, released as a limited preview on June 26, 2026. Terra and Luna were announced alongside it, giving three models that differ in performance and price for different uses. Let's look at where Sol sits, how it differs from Terra and Luna, and the pricing, in order.

What GPT-5.6 Sol Is (the flagship position)

GPT-5.6 Sol is OpenAI's strongest model to date, especially good at autonomous work in hard domains such as coding, biology, and cybersecurity. It is built for frontier reasoning and long, multi-step agentic tasks, and its home turf is "the hardest problems," like complex coding and security research.

How Sol, Terra, and Luna Differ (price and speed)

The three models split their roles along the balance of "performance" versus "cost and speed." Terra keeps performance on par with the previous generation, GPT-5.5, while holding the price to about 2x cheaper; it suits workloads that run large volumes. Luna, the fastest and cheapest in the family, fits light, routine work handled at low cost. In short, the basic split is Sol for hard problems, Terra for high volume, and Luna for light tasks.

GPT-5.6 Pricing Compared (per 1M tokens)

Pricing is usage-based on the number of tokens, with separate rates for input and output. The table below shows the official per-1M-token rates. Prices fall as you move from Sol toward Luna, and Luna costs one-fifth of Sol.

For a wider view of the major models, you may also find our ChatGPT (GPT-5) guide and What is Claude (Anthropic's generative AI) guide helpful.

GPT-5.6's New Features and Performance

What stands out in GPT-5.6 is a pair of new modes that control how the model thinks. With the same model, you can choose to have it think more deeply, or split the work to move faster. Let's look at what each does, and the official benchmark results.

What max reasoning effort Is (thinking more deeply)

max reasoning effort raises the model's "depth of thinking" to the maximum, letting it spend more time reasoning on hard problems. By deepening a single chain of reasoning, it lets Sol work through tough problems carefully. It helps in complex analysis and design where accuracy matters more than speed.

What ultra mode Is (subagents in parallel)

ultra mode takes the approach of "splitting" the work rather than "deepening" it. Instead of one model working alone, it hands complex work to several subagents (helper AI workers) and drives them together at high speed. It is said to be especially effective in coding, research, security review, and tool-heavy work. From the standpoint of running AI on several tasks in parallel day to day, having the work split up often finishes faster than asking a single model to think for a long time, so the intent behind ultra mode's subagent approach is easy to follow.

Benchmark Performance (Terminal-Bench, GeneBench)

OpenAI shared benchmark results across three areas: coding, biology, and cybersecurity. Sol set a new state of the art on Terminal-Bench 2.1, which measures command-line work requiring planning, iteration, and tool coordination. It is a result that backs up its strength in hard coding work.

There is progress beyond coding too. On GeneBench v1, which evaluates long-horizon genomics analysis, it achieved a higher score than GPT-5.5 while using fewer tokens. On the cybersecurity benchmark ExploitBench, it produced a comparable result while holding output tokens to about one-third. This efficiency—matching or beating with fewer tokens—is another feature of this release.

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Can You Use GPT-5.6 Sol Now (availability)

For all its capability, GPT-5.6 is not yet open to everyone. Let's look at the current scope, the U.S. government's request behind it, and the outlook for general availability.

Current Availability (API, Codex, limited preview)

Right now GPT-5.6 is a limited preview that only a select group of trusted partners and organizations can use, through the API and Codex. During the preview, access is confined to the API and Codex, so it is not yet available from everyday ChatGPT. The reach is limited to a small group of partners and organizations.

Limited Rollout at the U.S. Government's Request

Behind this limited rollout is a request from the U.S. government. OpenAI says it is starting with a limited preview for a small group of trusted partners whose participation has been shared with the government—a phased approach to releasing a highly capable model carefully. That said, OpenAI is clear that this kind of government access process should not become the long-term default.

For more on why the rollout is this cautious, you may also find our OpenAI Daybreak guide, focused on cyber defense, helpful.

GA Outlook and Safety

OpenAI says it plans to make GPT-5.6 Sol, Terra, and Luna generally available within the coming weeks. After further testing, it intends to move to broad availability in ChatGPT, Codex, and the API. It also says the models ship with its most robust safety stack to date, including protections for higher-risk activity, sensitive cyber requests, and repeated misuse.

On the cyber side, OpenAI says Sol does not reach the top "Cyber Critical" threshold in its Preparedness Framework. In evaluations involving Chromium and Firefox, it found bugs and exploitation primitives, but under the conditions tested it did not autonomously produce a fully working end-to-end exploit. Pairing stronger capability with stronger safeguards is what shows in this phased rollout.

GPT-5.6 Sol Summary

GPT-5.6 lines up three models—the top-end Sol, the cheaper Terra, and the fastest, cheapest Luna—to cover everything from hard problems to high volume and light tasks by use. With the new ultra mode and max reasoning effort, you can choose to think deeply or split the work to move faster, and it showed a high level on benchmarks such as Terminal-Bench 2.1. What you can reach today is limited to the API and Codex preview, but general availability is expected within the coming weeks, making this an update worth waiting for.

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