I honestly think of the T5 model family to sort of be the real beginning of this open model craze - I know BERT was already popular for classification etc, but T5 was the first sort of generally useful model, was exceptionally simple to fine-tune, and is still in use today (t5 base is still averaging over a million downloads a month on huggingface), has tons of variants and sort of kickstarted this whole community. US labs get a lot of flack but Google has been super supportive and open in a lot of ways that has pushed this whole endeavor forward, even if I feel like they've sort of declined in transparency in recent years with their open models.