Actually, they have release some details about it, in this 99-page technical report https://arxiv.org/abs/2303.08774 (which is actually two papers stitches together, once you read it; oddly enough using different fonts).
But I'm not sure if this content qualifies as "real details".
> Given both the competitive landscape and the safety implications of large-scale models like GPT-4, this report contains no further details about the architecture (including model size), hardware, training compute, dataset construction, training method, or similar. We are committed to independent auditing of our technologies, and shared some initial steps and ideas in this area in the system card accompanying this release. We plan to make further technical details available to additional third parties who can advise us on how to weigh the competitive and safety considerations above against the scientific value of further transparency.
In other words, "Stable Diffusion wasn't supposed to happen, so we're making all our methodology trade secret[0], if you want to Do Science then agree to this massive NDA and have enough skin in the game for us to cut you."
[0] Presumably at some point OpenAI will have to 'relent' to independent discovery by patenting AI architectures and refusing to license them
The other thing to note is that OpenAI is hosting ChatGPT as a public resource available to anyone with an account, akin to Google being open to the public from day one (although that is without an account. Maybe Gmail is a better comparison). I can't say for certain, only OpenAI would know for sure, but I'm willing to bet that inference for ChatGPT is the vast majority of their costs (which is all but trivial). Any private internal-only instance of OpenChatGPT (using the unlicensed leaked LLaMA model or a legal copy or someone else's) would need to pay (relatively) minuscule training costs, and way lower inference costs. Whether that cost can be borne by a small SaaS company's existing AWS budget is up in the air, which is to say ultimately that you're right - ChatGPT would be difficult without the support of Microsoft via a huge Azure grant, it's less obvious that self hosted OpenChatGPT, not from OpenAI, would be possible by hobbyist self-hosters with a prosumer GPU cluster (Say with last generation K80's instead of business-priced A100's), or by a company wanting to leverage LLMs for private use by companies that want to provide a Copilot like productivity multiplier tool to their developers, without sending private source code to OpenAI in lieu of a privacy agreement with them.