GPT-5.6 Sol
GPT-5.6 Sol was OpenAI's flagship for complex professional work before the GPT-6 family launched in September 2026. It remains available in the API with a 1.05M-token context window and reasoning effort from none to max.
Specifications
- Context window
- 1.05Mabout 788,000 words, or 1,580 pages
- Max output
- 125Ktokens per response
- Input price
- $4per 1M tokens
- Output price
- $20per 1M tokens
- Cached input
- $0.40per 1M tokens
- Weights
- ClosedProprietary
- Parameters
- Undisclosed
- Input types
- Text, Images
- Output types
- Text
- Reasoning mode
- Yes
- Tool calling
- Yes
- Released
- Jul 2026Legacy
Promotional standard rates from OpenAI's model page, which OpenAI says run at least through 2026-11-21. Prompts over 272K input tokens cost 2x input and 1.5x output. Cache writes cost 1.25x input. OpenRouter listed a different rate ($2/$10) at verification time.
What it costs in practice
| Workload | Monthly cost at list price |
|---|---|
| Support chatbot30,000 conversations a month, 2,000 input and 400 output tokens each | $480 |
| Document summaries2,000 documents a month, 12,000 input and 800 output tokens each | $128 |
| Coding agent1,000 tasks a month, 60,000 input and 6,000 output tokens each | $360 |
Standard rates, no caching or batch discounts. Run your own numbers.
Strengths
- 1.05M-token context window and 128K-token output limit
- Reasoning effort from none to max
- Full Responses API tool support, including computer use
Trade-offs to weigh
- Twice the per-token price of GPT-6.1 Sol
- Knowledge cutoff of February 16, 2026
Where it fits
OpenAI positions GPT-5.6 Sol for:
Where you can use it
- API
- OpenRouter
Alternatives to consider
| Model | Tier | Context | Input / output per 1M | |
|---|---|---|---|---|
| Claude Opus 5.5Anthropic | Frontier | 1M | $4 / $20 | Compare |
| Gemini 3.1 ProGoogle | Frontier | 1M | $2 / $12 | Compare |
| Kimi K3Moonshot AI | Frontier | 1M | $3 / $15 | Compare |
| Claude Fable 5.1Anthropic | Frontier | 1M | $10 / $50 | Compare |
Frequently asked questions
How much does GPT-5.6 Sol cost?
GPT-5.6 Sol lists at $4 per million input tokens and $20 per million output tokens, with cached input at $0.40 (checked October 10, 2026). Promotional standard rates from OpenAI's model page, which OpenAI says run at least through 2026-11-21. Prompts over 272K input tokens cost 2x input and 1.5x output. Cache writes cost 1.25x input. OpenRouter listed a different rate ($2/$10) at verification time. Confirm current rates on the provider's pricing page before you commit.
What is the context window of GPT-5.6 Sol?
GPT-5.6 Sol accepts up to 1,050,000 tokens of context (about 788,000 words, or 1,580 pages), and it can write up to 125K tokens in a single response. Long prompts cost more and can be slower, so most apps send only what the task needs.
Is GPT-5.6 Sol open source?
No. GPT-5.6 Sol is a proprietary model from OpenAI; its weights aren't published. You can use it through the OpenAI API and through OpenRouter.
What is GPT-5.6 Sol best for?
OpenAI positions GPT-5.6 Sol for coding, agents, reasoning, enterprise. It accepts text, images as input, has a reasoning (thinking) mode and supports tool calling. Test it on a sample of your own tasks before you choose it for production.
Sources
- developers.openai.com/api/docs/models/gpt-5.6-sol
- developers.openai.com/api/docs/pricing
- developers.openai.com/api/docs/models/gpt-5.6-sol.md
- developers.openai.com/api/docs/pricing?no_head=1
- openai.com/index/introducing-gpt-6-sol-and-luna
- openrouter.ai/~openai
- docs.perplexity.ai/docs/agent-api/models.md
Facts checked against these pages on October 10, 2026. Spot an error? Tell us.
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