Claude.ai, ChatGPT, etc. are finished B2C products. They're black boxes, encapsulated experiences. Consumers don't want to pick a model, or know what model they're using; they just want to "talk to AI", and for the system to know which model is best to answer any given question. I would bet that for these companies, if their frontend observes you using the little model override button, that gets instrumented as an "oops" event in their metrics — something they aim to minimize.
What you're looking for, are the landing pages of the B2B API products underlying these B2C experiences. That would be https://www.anthropic.com/claude, https://openai.com/api/, etc. (In general, search "[AI company] API".)
From those B2B landing pages, you can usually click through to pages with details about each of their models.
(Also, note how these B2B pages are on the AI companies' own corporate domains; whereas their B2C products have their own dedicated domains. From their perspective, their B2C offerings are essentially treated as separate companies that happen to consume their APIs — a "reference use-case" — rather than as a part of what the B2B company sells.)
What you're looking for, are the landing pages of the B2B API products underlying these B2C experiences. That would be https://www.anthropic.com/claude, https://openai.com/api/, etc. (In general, search "[AI company] API".)
From those B2B landing pages, you can usually click through to pages with details about each of their models.
Here's the model page corresponding to this news announcement, for example: https://www.anthropic.com/claude/opus
(Also, note how these B2B pages are on the AI companies' own corporate domains; whereas their B2C products have their own dedicated domains. From their perspective, their B2C offerings are essentially treated as separate companies that happen to consume their APIs — a "reference use-case" — rather than as a part of what the B2B company sells.)