Pretty sure Google fits any definition of major model maker that SpaceX does, and had their IPO long before SpaceX.

Meta and Microsoft both are also significant makers of GenAI models that are public, though neither has a big tentpole LLM line that they sell access.to commercially like OpenAI, Anthropic. Google, SpaceX, which I infer might be what you mean by major model maker.

Meta had Llama, which set a lot of things on fire in a good way, and then disappeared from the scene as tech advanced.

What does Microsoft have?

Not sure SpaceX counts. Nobody sane uses Grok. It's untrustable due to reality-distorting political bias training, and it's strongly associated with CSAM production. Not what you want in a reliable corporate utility.