You either include all labs which can reasonably produce models which are capable enough to be considered generally on-par with the best available models, in which case there has been way more than 2 frontier labs for a while now, or you take a more literal definition and only include labs which are capable of producing models which are considered "the best" out there, in which case there are basically just 2.

I think the former definition is a bit more meaningful since it avoids issues with determining what actually constitutes "the best" model out there. In that case, Google has been a frontier lab for a long time, Meta arguably as well, and you're also ignoring xAI which has been competitive for a while now. And, obviously, there's a bunch of Chinese labs which would deserve the title as well.

But if one is being strict (and willing to accept generally accepted definitions/measures/etc.), then there has only ever been two frontier labs: OpenAI and Anthropic. They're the only labs to have had "the best" models at any point in time since LLMs became a thing.

Google definitely had the best model at points if you're not only concerned with coding, but then they didn't release any pro models for 8 months