Competition in a duopoly looks very different from competition with a large number of suppliers.

nah if not for open models they'd just raise the price in unison as any self respecting oligopoly would.

They'd compete on model quality, sure, but without competition from open models there is no reason to compete on price

Neither OpenAI or anthropic can afford to lose subscribers to the other or anybody else right before IPO. I tried both CC and codex recently, and I would say they are practically on par. Some things CC does better, some things codex does better. I've also seen them increase usage limits. The cheapest plan now feels very generous imo.