ChatGPT 5.6 (GPT-5.6): Sol, Terra, and Luna — Everything You Need to Know

OpenAI released GPT-5.6 on July 9, 2026, as a three-tier model family — Sol, Terra, and Luna — all sharing a 1.05-million-token context window and a new pricing structure starting at $1 per million input tokens. GPT-5.6 is now available across ChatGPT, Codex, and the OpenAI API. The family is designed to cover every workload: Sol handles the hardest reasoning and coding tasks, Terra matches GPT-5.5 quality at roughly half the cost, and Luna targets fast, high-volume pipelines where price per token is the primary constraint. Despite the general availability announcement, GPT-5.5 Instant remains the default in standard ChatGPT — details that matter before migrating any workflow.

What Is GPT-5.6? Release Date and Background

GPT-5.6 — formally Generative Pre-trained Transformer 5.6 — is OpenAI’s newest model generation and a deliberate departure from the single-model convention used by predecessors. Rather than releasing one large model, OpenAI built three distinct capability tiers that share a common architecture, knowledge base, and context window.

The general availability launch date is July 9, 2026. A limited preview had opened on June 26, 2026 for a small group of trusted partners. The phased rollout was coordinated at the request of the U.S. government, which had concerns about the models’ elevated cybersecurity capabilities. This makes GPT-5.6 the first OpenAI model generation to undergo explicit pre-launch government coordination before general release.

What changed from GPT-5.5

GPT-5.5 Instant is not being deprecated — it remains the default for fast everyday responses in standard ChatGPT. GPT-5.6 runs alongside it as a parallel expansion. The main structural changes:

• Three permanent capability tiers (Sol, Terra, Luna) replace the single-model convention
• Two new reasoning controls — max and ultra — push Sol beyond the standard compute ceiling
• CEO Sam Altman stated that Sol is 54% more token-efficient for AI coding tasks versus previous versions
• Terra is competitive with GPT-5.5 while costing approximately half as much
• Programmatic Tool Calling and improved multi-agent orchestration are new for the API

Knowledge cutoff and specs shared by all three models

All three GPT-5.6 models share the same infrastructure parameters:

GPT-5.6 Sol vs Terra vs Luna: Tier Differences Explained

The naming convention in GPT-5.6 is new: the version number (5.6) marks the generation, and the name (Sol, Terra, Luna) marks the capability tier. Each tier can advance on its own release schedule — so future releases may update one tier without touching the others.

The plain API alias gpt-5.6 routes to gpt-5.6-sol, not to a router that selects among tiers automatically. Developers who want Terra or Luna must specify the model ID explicitly.

GPT-5.6 Sol — Flagship workhorse

Sol is the strongest model in the family and the one OpenAI benchmarks in every headline result. It is the only tier that unlocks two new reasoning controls:

max reasoning effort gives Sol the most compute time available to work through a single-agent problem. It is the appropriate setting when a task is difficult enough that a failed attempt would be expensive to redo.

ultra mode goes further by deploying subagents in parallel to accelerate complex multi-step tasks. The resulting variant — GPT-5.6 Sol Ultra — posts the family’s highest scores across benchmarks.

Sol is the preferred model for Microsoft Copilot 365 and powers ChatGPT Work. Best fit: complex reasoning, agentic coding, cybersecurity, scientific research, computer use, and high-value knowledge work. For a detailed breakdown of Sol’s benchmark scores and pricing, see the OpenAI Sol model guide.

GPT-5.6 Terra — Balanced everyday model

Terra is positioned as the practical default for professional workloads — GPT-5.5-level quality at roughly half the cost. On the Artificial Analysis Coding Agent Index it scores slightly above Anthropic’s Fable 5, placing it solidly mid-tier by capability while remaining the most cost-effective option for sustained production use.

Terra lacks the max and ultra reasoning controls available to Sol. Best fit: everyday professional work, analysis, routine coding help, document drafting, and balanced production routing. Compare Terra’s pricing against Sol in the OpenAI Terra model breakdown.

GPT-5.6 Luna — Fast, low-cost tier

Luna is the fastest and most affordable option, optimized for latency-sensitive or budget-sensitive pipelines. Despite being the cheapest tier, Luna outperforms Claude Opus 4.8 on the Artificial Analysis Coding Agent Index — “cheapest” does not mean “weakest” across all tasks.

Best fit: extraction, classification, first-draft generation, routing logic, and high-volume work that is easy to verify or retry. See latency benchmarks and use cases in the OpenAI Luna model guide.

GPT-5.6 Benchmarks: Sol, Terra, and Luna Performance Data

The GPT-5.6 family was evaluated across four main benchmark categories: coding agent performance, terminal workflows, advanced reasoning, and medical knowledge.

Coding: Artificial Analysis Coding Agent Index

Sol’s score of 80 is 2.8 points above Fable 5 — see the full GPT-5.6 vs Claude Fable 5 comparison for the head-to-head breakdown. OpenAI notes that Sol achieves this while using fewer than half the output tokens, completing tasks in less than half the time, and costing approximately one-third less than Fable 5. The efficiency gap is as significant as the accuracy gap.

Sol is 54% more token-efficient for AI coding tasks — a direct consequence of the architectural work we put into GPT-5.6 to make agentic loops less verbose and more precise.

Sam Altman, CEO, OpenAI

Coding: Terminal-Bench 2.1

Terminal-Bench 2.1 tests command-line workflows that require iteration, error recovery, and tool coordination — a closer proxy for real developer work than static coding puzzles.

One notable result: on this benchmark, Claude Mythos 5 ties GPT-5.5 at the top of the competitor group, while Terra (87.4%) outscores GPT-5.5 (85.6%) — consistent with OpenAI’s “competitive with GPT-5.5 overall” positioning for Terra.

Reasoning and Health

On Agents’ Last Exam, GPT-5.6 Sol scores 52.7% versus GPT-5.5’s 46.9% — a 5.8-point improvement on one of the most demanding multi-step reasoning evaluations available.

On HealthBench Professional (length-adjusted), Sol scores 60.5 (+8.7 versus GPT-5.5), Terra scores 57.7, and Luna scores 55.7. All three GPT-5.6 tiers outperform GPT-5.5’s baseline of 51.8 on this benchmark.

GPT-5.6 Pricing: API Costs and Long-Context Rates

Pricing is tiered by model and by context length. Requests above 272,000 input tokens cross into a long-context pricing band.

Standard API pricing (short context, per 1M tokens)

Long-context pricing (above 272K input tokens)

The 2x input / 1.5x output multiplier applies to the entire request once the 272K threshold is crossed — not just the tokens above the threshold.

Prompt caching

Prompt caching is supported across all three models via the Responses API:

• Cache writes: billed at 1.25x the uncached input rate
• Cached reads: 90% discount off the standard input rate
• Minimum cache lifetime: 30 minutes

On workflows with long, repeated system prompts or reference documents, the 90% cached-read discount substantially reduces effective cost per request after the first call. For a Sol workload running 1,000 requests against a 100K-token cached system prompt, the cached-read discount drops the effective input cost from $500 to approximately $50 for that cached portion.

For current and updated pricing figures, check the OpenAI API pricing page directly.

How to Access GPT-5.6 in ChatGPT, Codex, and the API

Access varies significantly by product surface. The key distinction that catches most users off-guard: GPT-5.5 Instant remains the everyday default in standard ChatGPT. GPT-5.6 Sol appears through reasoning settings on paid plans, not as the primary chat model.

Access by surface

Terra and Luna are not selectable in standard ChatGPT conversations regardless of plan. They are accessible through the Codex coding agent, ChatGPT Work, and the API. For developers integrating GPT-5.6 into pipelines, see how OpenAI Programmatic Tool Calling works with all three tiers.

How to switch to GPT-5.6 Sol on ChatGPT Plus — step by step

1. Log in to ChatGPT with a Plus, Pro, Business, or Enterprise account.
2. Open a new conversation.
3. Click the model selector dropdown at the top of the chat window.
4. Select GPT-5.6 or navigate to Reasoning settings.
5. Choose Medium or High reasoning effort to activate Sol.
6. For ultra mode, switch to Codex (accessible from the ChatGPT Work interface or the sidebar) and select Ultra effort.
7. For API access, set model: "gpt-5.6-sol" (or "gpt-5.6-terra" / "gpt-5.6-luna") in your request parameters.

Cerebras-hosted Sol

OpenAI is launching GPT-5.6 Sol on Cerebras infrastructure at up to 750 tokens per second for latency-sensitive workloads. This is initially available to select customers as capacity expands — the combination of Sol’s quality and Cerebras throughput is aimed at real-time agentic applications where response lag breaks the user experience.

GPT-5.6 Safety, Preparedness Framework, and Government Coordination

Safety evaluation for the GPT-5.6 family was more extensive than for any prior OpenAI release. The full documentation is published in the GPT-5.6 Preview System Card on OpenAI’s Deployment Safety Hub.

Under OpenAI’s Preparedness Framework, all three models received identical risk designations:

• High in Biological and Chemical risk
• High in Cybersecurity
• Below High in AI Self-Improvement

This marks the first time that Terra and Luna — smaller, faster members of a model family — received a High designation in any Preparedness-tracked category. Prior releases typically reserved High ratings for the largest flagship models only.

Red-teaming at scale

OpenAI dedicated over 700,000 A100-equivalent GPU hours to automated red-teaming aimed at finding universal jailbreaks — attacks that generalize across prompts and contexts rather than exploiting specific phrasing. Automated red-teaming continues during live deployment, not just in pre-launch testing.

The cybersecurity findings illustrate why the models received a High designation. GPT-5.6 Sol saturates the internal Capture-the-Flag evaluation at 96.7%. On FrontierCyber, Sol scores 11% Easy, 12% Medium, 5% Hard, and 0% Elite. Sol and Terra can identify vulnerabilities and compose pieces of exploits, but were unable to carry out autonomous end-to-end attacks against hardened targets in testing — the basis for classifying them as High rather than Critical in cybersecurity.

Layered safety stack

OpenAI describes the defense-in-depth approach for GPT-5.6 across several layers:

• Model-level safety training baked into all three tiers
• Activation classifiers on Sol and Terra that can intervene during generation
• Real-time output scanning on the API serving layer
• Automated pattern-detection across conversation streams

The framework argues that severe harm requires a chain of successful steps, and safeguards placed at multiple points in that chain reduce end-to-end risk even when individual layers are imperfect.

ChatGPT Work: GPT-5.6 for Enterprise Teams

ChatGPT Work launched on July 9, 2026 — the same day as GPT-5.6 general availability — and is powered by GPT-5.6 Sol. It is OpenAI’s agentic assistant for workplace teams, built to automate multi-step tasks across files, apps, and workflows rather than answer individual questions.

At launch, 5+ million users were using Codex weekly, with 1+ million using it beyond software development. The new unified ChatGPT desktop app for Mac and Windows replaces the legacy Codex app (the legacy app is now renamed ChatGPT Classic).

Key capabilities

Plan Mode changes how ChatGPT approaches complex requests. Instead of executing immediately, the assistant gathers context, asks clarifying questions, creates a step-by-step plan, and only then begins execution. This reduces silent failures in long agentic workflows.

Computer Use lets ChatGPT click, type, and manage files across desktop applications on the user’s behalf — without requiring the user to set up browser automation or shell scripts.

Sites (beta) converts completed work — reports, dashboards, research summaries — into shareable, interactive web applications that non-technical stakeholders can open without special tooling.

Scheduled Tasks handles one-time or recurring workflows that execute offline, appropriate for batch processing, overnight reports, and monitoring tasks.

Plugin integrations cover 1,400+ services including Slack, Microsoft Teams, Google Drive, SharePoint, email, calendars, and CRMs.

ChatGPT Work pricing

ChatGPT Work competes directly with Anthropic’s Claude Cowork and Microsoft Copilot Cowork for the enterprise AI assistant market. See full feature and pricing details in the ChatGPT Work enterprise guide.

GPT-5.6 vs GPT-5.5: What Actually Changed?

GPT-5.5 Instant remains the default for fast responses in standard ChatGPT. GPT-5.6 is not a straight replacement — it is a parallel expansion that adds a three-tier structure alongside existing models. The practical differences for developers and teams:

The most significant practical change for API developers is prompt caching behavior: the new 90% discount on cached reads makes long system prompts economical at scale in a way they were not under GPT-5.5’s caching implementation.

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