Can I use both Gemini 3.1 Pro and GPT-5.5 through one API?

Yes. ApexApi serves both behind one OpenAI-compatible endpoint and a single ak- key. Switch between them by changing the model slug, so you can A/B them on your own prompts without re-integrating.

Which is cheaper, Gemini 3.1 Pro or GPT-5.5?

Live per-token prices for both are in the table above. Pricing changes over time, so the table reflects the current catalog rather than a fixed number.

How do I switch from Gemini 3.1 Pro to GPT-5.5?

Change one string, the model slug, in your request. Same endpoint, same key, same billing. No new account or SDK.

Gemini 3.1 Pro vs GPT-5.5

The short answer

Gemini 3.1 Pro is built around deep native multimodality and very long context, so it shines when you feed it large mixed inputs like documents, images, and long transcripts. GPT-5.5 centers on instruction fidelity and reliable tool use, which makes it a strong default for agents and automation. Pick Gemini when context length and multimodal grounding dominate; pick GPT-5.5 when tool orchestration and predictable instruction-following matter most. Both share one key on ApexApi, so testing both is a slug change.

At a glance

	Gemini 3.1 Pro Preview	GPT-5.5
Maker	Google AI	OpenAI
Type	chat	chat
Context window	1,048,576 tokens	1,050,000 tokens
Vision input	Yes	Yes
Tool calling	Yes	Yes
Input price	$2.40 /1M	$6.00 /1M
Output price	$14.40 /1M	$36.00 /1M

Prices are live from the catalog and include our service fee.

When to choose Gemini 3.1 Pro Preview

•You process very long or multimodal inputs (long docs, images, audio).
•Native grounding across modalities is central to the task.
•You want the largest practical context window.

Gemini 3.1 Pro Preview API details →

When to choose GPT-5.5

•Reliable function calling and structured output are the priority.
•You are building tool-using agents and automation.
•You want consistent, predictable instruction-following.

GPT-5.5 API details →

Call both through one API and key

ApexApi serves Gemini 3.1 Pro Preview and GPT-5.5 behind a single OpenAI-compatible endpoint. A/B them by changing one string.

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Frequently asked questions

Can I use both Gemini 3.1 Pro and GPT-5.5 through one API?: Yes. ApexApi serves both behind one OpenAI-compatible endpoint and a single ak- key. Switch between them by changing the model slug, so you can A/B them on your own prompts without re-integrating.
Which is cheaper, Gemini 3.1 Pro or GPT-5.5?: Live per-token prices for both are in the table above. Pricing changes over time, so the table reflects the current catalog rather than a fixed number.
How do I switch from Gemini 3.1 Pro to GPT-5.5?: Change one string, the model slug, in your request. Same endpoint, same key, same billing. No new account or SDK.