Quick answer
The current GPT-5.6 Sol, Terra, and Luna API models list a 1,050,000 tokens context window and a separate 128,000 tokens maximum output. Always match the exact model ID you deploy.
Verified Aug 22, 2026Official source
Current limits
| Constraint | Current value | Scope | Verified source |
|---|---|---|---|
| GPT-5.6 Sol / Terra / Luna context windowModel-specific API context window; output is also bounded separately. | 1,050,000 tokens | GPT-5.6 | OpenAIAug 22, 2026 |
| GPT-5.6 maximum outputSeparate output ceiling shown for the current GPT-5.6 Sol, Terra, and Luna models. | 128,000 tokens | GPT-5.6 | OpenAIAug 22, 2026 |
Why does this limit matter?
The context window is a shared budget across instructions, conversation state, retrieved material, tool data, and generated tokens.
A large context ceiling does not mean the model can generate that many output tokens; output has its own cap.
What should you check?
- Confirm the exact API model ID in your request.
- Read that model's current catalog entry.
- Count prompt and expected output tokens with a safety margin before dispatch.
Important caveats
- Older and specialized models have different limits.
- API context specifications do not automatically describe ChatGPT product allowances.
HyperObserve reports the documented platform constraint. Your application, SDK, gateway, provider, region, or account can impose a lower effective limit.
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