The source is the GPT 5.5 System Card:

> We generally treat GPT-5.5’s safety results as strong proxies for GPT-5.5 Pro, which is the same underlying model using a setting that makes use of parallel test time compute. As noted below, we separately evaluate GPT-5.5 Pro in certain cases because we judge that the setting could materially impact the relevant risks or appropriate safeguards posture.

https://deploymentsafety.openai.com/gpt-5-5/model-data-and-t...

There have been multiple podcasts with people from OpenAI which have confirmed this.

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cubefox 2 hours ago | parent [-]

> makes use of parallel test time compute

Any idea what that means exactly? I vaguely remember that ChatGPT Pro was originally called "deep thought", just like Geminis "deep thought" feature (or "deep think"?), so it seems likely they are using the same approach.

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nl 2 hours ago | parent [-]

Their methodology isn't published.

Its widely accepted[1] that it runs the same query through the model in parallel and then has a model that either selects the best answer or synthesizes an answer from the multiple ones generated.

I believe most people think it runs 6 sub-models, but I think that is based on the pricing.

It's a pity that OpenAI doesn't publish details like this.

[1]eg https://news.ycombinator.com/item?id=48799977

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dannyw 2 hours ago | parent [-]

Basically like passes@6 or passes@5 if you’re doing a benchmark, except for your real tasks.

Pro is quite limited on the web UI I reckon. This approach can be highly effective for reasonably verifiable task, for example, write comprehensive unit tests pointing out a tricky bug, get multiple agents to swarm at it.

	▲	nl 2 hours ago \| parent [-]
		It's been very successful at frontier math tasks - a bunch of the Erdos questions have been solved by it - more than any other model. https://www.erdosproblems.com/