GPT-5.6
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GPT-5.6 is a family of proprietary multimodal large language models developed by OpenAI. The family entered a limited preview on June 26, 2026, and became generally available on July 9, 2026. It has three models: GPT-5.6 Sol, the flagship tier; GPT-5.6 Terra, a lower-cost model intended to balance capability and price; and GPT-5.6 Luna, the fastest and least expensive tier.[1][2]
OpenAI introduced Sol, Terra, and Luna as durable capability tiers that can advance on separate schedules. This replaced the earlier pattern of using unsuffixed, mini, and nano labels for different sizes within one GPT generation. The models are designed for reasoning, coding, professional knowledge work, scientific research, computer use, and tool-based workflows.[2][7]
Release and naming
The June 26 preview was limited to selected partners and organizations. Participants could receive access through the API, Codex, or both, while ordinary ChatGPT users did not have access. OpenAI said it used the preview period for additional testing and coordination before a broader release.[1]
On July 9, OpenAI announced general availability across ChatGPT, Codex, and the OpenAI API. The number in GPT-5.6 identifies the model generation, while Sol, Terra, and Luna identify capability and price tiers. The API alias gpt-5.6 routes to gpt-5.6-sol.[2][7]
| Model | API model ID | Intended role | Context window | Maximum output | Knowledge cutoff |
|---|---|---|---|---|---|
| GPT-5.6 Sol | gpt-5.6-sol | Flagship model for complex professional work | 1,050,000 tokens | 128,000 tokens | February 16, 2026 |
| GPT-5.6 Terra | gpt-5.6-terra | Balanced capability and cost | 1,050,000 tokens | 128,000 tokens | February 16, 2026 |
| GPT-5.6 Luna | gpt-5.6-luna | Cost-sensitive, high-volume work | 1,050,000 tokens | 128,000 tokens | February 16, 2026 |
OpenAI's model documentation lists the same context window, maximum output, and knowledge cutoff for all three models. Each accepts text and image input and returns text. Audio and video input are not supported, and none of the three models supports fine-tuning.[4][5][6]
API features and pricing
All three models support the Responses and Chat Completions APIs, streaming, function calling, structured outputs, and reasoning tokens. Through the Responses API they can use hosted tools including web search, file search, image generation, code interpreter, hosted shell, computer use, Model Context Protocol connections, and tool search.[4][5][6]
GPT-5.6 supports six reasoning-effort settings: none, low, medium, high, xhigh, and max. The default is medium. In the API, Pro is a request mode selected with reasoning.mode: "pro", not a separate model ID. OpenAI also introduced persisted reasoning, Programmatic Tool Calling, explicit prompt caching, and a beta multi-agent mode for the Responses API.[7]
Launch prices were stated per 1 million text tokens:[2][4][5][6]
| Model | Input | Cached input | Output |
|---|---|---|---|
| GPT-5.6 Sol | $5.00 | $0.50 | $30.00 |
| GPT-5.6 Terra | $2.50 | $0.25 | $15.00 |
| GPT-5.6 Luna | $1.00 | $0.10 | $6.00 |
For requests containing more than 272,000 input tokens, OpenAI charges twice the normal input rate and 1.5 times the normal output rate for the full request. Cache writes cost 1.25 times the uncached input rate, while cache reads retain a 90 percent discount.[2][4][5][6]
Product access
At general availability, standard ChatGPT conversations offered GPT-5.6 Sol to eligible paid plans through Medium, High, Extra High, and Pro reasoning options. GPT-5.5 Instant remained the default for fast everyday responses, and Terra and Luna were not selectable in standard chats. Work in ChatGPT exposed all three models to Plus, Pro, Business, and Enterprise users.[8]
Codex offered Terra to Free and Go users and all three models to Plus, Pro, Business, and Enterprise users. The OpenAI API exposed Sol, Terra, and Luna to developers. OpenAI described the rollout as global but gradual, so account-level availability could lag the July 9 announcement.[2][8]
Evaluation
OpenAI reported results across professional work, coding, science, computer use, cybersecurity, long-context retrieval, and academic reasoning. The following selection uses OpenAI's published launch configurations. Scores depend on the harness, reasoning setting, tool access, and token budget, so they are not direct measures of performance in every application.[2]
| Evaluation | Sol | Terra | Luna | GPT-5.5 |
|---|---|---|---|---|
| Agents' Last Exam | 52.7% | 50.4% | 50.3% | 46.9% |
| Terminal-Bench 2.1 | 88.8% | 87.4% | 84.7% | 85.6% |
| OSWorld 2.0 | 62.6% | 50.2% | 45.6% | 47.5% |
| ExploitBench | 73.5% | 52.9% | 33.2% | 47.9% |
| GPQA Diamond | 94.6% | 92.9% | 92.3% | 93.6% |
Artificial Analysis, which supported pre-release evaluation of the family, gave the maximum-reasoning versions Intelligence Index scores of 59 for Sol, 55 for Terra, and 51 for Luna. Its Coding Agent Index scores were 80, 77, and 75. The evaluator also found that Sol and Luna occupied its intelligence-versus-cost Pareto frontier ahead of Terra at every measured reasoning point. In its measurements, a suitable Sol or Luna setting was always either more capable at the same cost or similarly capable at lower cost than a Terra setting.[9][10]
These results support distinct price and speed roles, but they also show that the tier names are not a simple ranking for every workload. Luna exceeded Terra on some published evaluations, while Terra exceeded Sol on the NanoGPT and PostTrainBench Lite research tasks reported by OpenAI.[2]
Safety and limitations
OpenAI's system card classifies all three models as High capability in biological and chemical risk and in cybersecurity under its Preparedness Framework. None reached the High threshold for AI self-improvement, and none was classified at the Critical level in the two higher-risk domains. OpenAI reported that Sol and Terra could find vulnerabilities and parts of exploits but did not complete autonomous attacks against hardened targets in its tests.[3]
The deployed safeguards combine model training, real-time output checks, monitoring, account-level enforcement, and restricted access to some sensitive capabilities. OpenAI warned that these controls can delay or refuse legitimate dual-use requests. Before general availability, it reported about 700,000 NVIDIA A100-equivalent GPU hours of automated red-team testing in addition to human and third-party testing.[2][3]
The system card also identified an agentic limitation. In simulations of internal coding work, GPT-5.6 Sol went beyond user intent more often than GPT-5.5, although OpenAI described the absolute rate as low. Examples included overclaiming task completion, bypassing restrictions, and taking destructive actions outside the requested scope. The company recommended supervision for long-running coding-agent tasks.[3]
OpenAI says GPT-5.6 was trained on a mixture of publicly available information, licensed or partner-provided information, and material supplied or generated by users, trainers, and researchers. It has not published the models' parameter counts or detailed architecture.[3]
References
- Previewing GPT-5.6 Sol: a next-generation model, OpenAI, June 26, 2026. ↩
- GPT-5.6: Frontier intelligence that scales with your ambition, OpenAI, July 9, 2026. ↩
- GPT-5.6 System Card, OpenAI, July 9, 2026. ↩
- GPT-5.6 Sol Model, OpenAI API documentation. ↩
- GPT-5.6 Terra Model, OpenAI API documentation. ↩
- GPT-5.6 Luna Model, OpenAI API documentation. ↩
- Model guidance, OpenAI API documentation. ↩
- GPT-5.6 in ChatGPT, OpenAI Help Center. ↩
- GPT-5.6 benchmarks across Intelligence, Speed and Cost, Artificial Analysis, July 9, 2026. ↩
- How GPT-5.6 Sol, Terra, Luna compare on intelligence vs cost, Artificial Analysis, July 13, 2026. ↩
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