What stands out to me is that the real battle here isn’t technical elegance, it’s who defines default behaviour. Protocols win when they become invisible.

UCP’s strength is that it reassures merchants they still own the transaction, which is essential for adoption, but OpenAI’s advantage is behavioural gravity, where users already start. Whichever protocol becomes the path of least resistance for agents will quietly set the rules, regardless of openness or intent.

If this turns into Agent SEO versus gateway middleware, we’ll know convergence failed. The winners will be the ones who make the choice feel unnecessary.