Current as of March 2026. GPT-5 Pro is OpenAI’s flagship reasoning model, offering a 400K context window and a massive 128K output limit. It is powerful but comes with a high price tag of $120 per million output tokens.
Specs
| Provider | OpenAI |
| Input cost | $15 / M tokens |
| Output cost | $120 / M tokens |
| Context window | 400K tokens |
| Max output | 128K tokens |
| Parameters | N/A |
| Features | function_calling, vision, reasoning, web_search |
What it’s good at
Reasoning Capability
The model excels at complex logic and multi-step problem solving that trips up smaller models.
Output Capacity
A 128K output limit allows for generating entire technical books or massive code modules in a single request.
Where it falls short
Output Pricing
At $120 per million tokens, the output cost is eight times higher than the input cost, which burns through budgets quickly.
Inference Latency
The deep reasoning features cause a noticeable delay before the model starts streaming responses.
Best use cases with OpenClaw
- Large-Scale Refactoring — Use this when you need to ingest 400K tokens of legacy code and output a completely rewritten architecture.
- Complex Agent Tasks — Its native web search and function calling make it the most reliable engine for OpenClaw agents performing research.
Not ideal for
- High-Volume Simple Tasks — Basic classification or summarization should be offloaded to cheaper models like GPT-4o-mini to save money.
- Low-Latency Apps — If your users expect a response in under two seconds, the reasoning overhead here will be a dealbreaker.
OpenClaw setup
OpenClaw includes native support for this model; just export your OPENAI_API_KEY and the framework handles the rest without custom configuration.
export OPENAI_API_KEY="your-key-here"
That’s it. OpenClaw picks up OpenAI models automatically.
How it compares
- vs Claude 3.5 Sonnet — Claude is significantly more affordable and often faster, though it lacks the 128K output ceiling of GPT-5 Pro.
- vs Gemini 1.5 Pro — Gemini offers a much larger 2M context window for a lower price, but its reasoning is less consistent for complex coding tasks.
Bottom line
Use GPT-5 Pro for the hardest reasoning problems where cost is secondary to accuracy and massive output length.
For setup instructions, see our API key guide. For all available models, see the complete models guide.