GPT-5.6 Sol

GPT-5.6 Sol remains OpenAI's generally available lower-cost frontier route while GPT-6 Astra rolls out beyond Trusted Access organizations; use Sol for complex professional work, hard reasoning, software engineering, and scientific tasks when Astra access or price is not justified.

Platform: OpenAI

Language ModelReasoningCodingOpenAI

OpenAI-hosted

Promotional through at least November 21, 2026: $4/1M input, $0.40/1M cached input, and $20/1M output; prompts above 272K input use $8 input and $30 output rates; cache writes cost 1.25x uncached input

Commercial

🚀Function Overview

The frontier GPT-5.6 tier for difficult professional, reasoning, and coding tasks where stronger capability justifies a higher per-token price.

Key Features

Official OpenAI GPT-5.6 family member with model ID gpt-5.6-sol
OpenAI's frontier GPT-5.6 tier and the target of the gpt-5.6 alias
Generally available across the OpenAI API, ChatGPT, and Codex
Acknowledged by a July 2026 mathematics paper for suggesting the counterexample construction idea later verified and proved by the authors
1,050,000-token context window and 128,000-token maximum output
February 16, 2026 knowledge cutoff with reasoning-token support
Promotional pricing of $4 input, $0.40 cached input, and $20 output per 1 million tokens through at least November 21, 2026
Prompts above 272K input tokens use 2x input and 1.5x output rates; cache writes use 1.25x uncached input

Use Cases

•Escalating difficult Codex software engineering tasks
•Testing high-stakes reasoning tasks before choosing a production model route
•Generating candidate mathematical constructions for human proof and computer-algebra verification
•Comparing Sol against cheaper GPT-5.6 Terra or Luna runs
•Evaluating long-context, cache-write, and output-token costs before broad rollout

⚙️Input Parameters

messages

array

Chat or reasoning task messages sent to the OpenAI API or through a supported OpenAI product surface.

model

string

Use gpt-5.6-sol for the explicit Sol tier or gpt-5.6 for the alias that OpenAI routes to Sol.

reasoning_effort

string

Choose a supported reasoning effort for the task; OpenAI positions max for harder work and exposes multi-agent orchestration separately in the Responses API beta.

💡Usage Examples

Example 1

Input Parameters

{
  "model": "gpt-5.6-sol",
  "messages": [
    {
      "role": "user",
      "content": "Review this failing distributed-systems test and propose the smallest verified fix."
    }
  ],
  "reasoning_effort": "max"
}

Output Results

A response from GPT-5.6 Sol. Validate quality and total cost against Terra or Luna before making Sol the production default.

Quick Actions

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Technical Specifications

Hardware Type: OpenAI-hosted
Commercial Use: Supported
Pricing: Promotional through at least November 21, 2026: $4/1M input, $0.40/1M cached input, and $20/1M output; prompts above 272K input use $8 input and $30 output rates; cache writes cost 1.25x uncached input
Platform: OpenAI