This post (I Built Non-Autoregressive Decision Models with RL a Year Ago. Then a Frontier Lab Called It a "Breakthrough") seems useful though fairly technical https://laya.convaiinnovations.com/
CLIP (https://openai.com/index/clip) is simpler but very applicable. There's a general pre-training task with no extra steps, and you get a model that scores an image against the text labels you provided.
Maybe what's confusing is that an LLM outputs next-token probabilities over a fixed vocab, so there's a jump inherent to taking that same model and having it outpu... (read more)
On page 140 here https://storage.googleapis.com/deepmind-media/gemini/gemini_4_safety_report.pdf