Is GPT-5.5 Pro available on FastMetal?

Not at the moment. GPT-5.6 Sol, from the same lab, is available on the FastMetal API today.

What is the context window of GPT-5.5 Pro?

1,050,000 tokens, shared between the prompt and the response.

openai/gpt-5-5-pro

Not Available

GPT-5.5 Pro

GPT-5.5 Pro is OpenAI’s high-capability model optimized for deep reasoning and accuracy on complex, high-stakes workloads. It features a 1M+ token context window (922K input, 128K output) with support for...

4/24/2026

1,050,000 tokens

Specifications

Modalities

Input

file

image

text

Output

text

Supported Parameters

include_reasoning

max_tokens

reasoning

reasoning_effort

response_format

seed

structured_outputs

tool_choice

tools

Max Output Tokens

128,000

Reasoning Configuration

Default: Thinking on (effort: medium)
Selectable effort levels: xhigh
high
medium
Turning thinking off: Not possible (always thinks)

How to control thinking, and what it costs

Frequently asked questions

Is GPT-5.5 Pro available on FastMetal?: Not at the moment. GPT-5.6 Sol, from the same lab, is available on the FastMetal API today.
What is the context window of GPT-5.5 Pro?: 1,050,000 tokens, shared between the prompt and the response.

Models you can use on FastMetal