Possibly OAI? If you have OAI tokens you are a captive audience. If you have OpenRouter you are bidding on a free market.

OpenRouter attributes this promotion to OpenAI https://x.com/OpenRouter/status/2089416739398254662

Why though, to AB test/see the impact of a price cut on a platform with multiple competitors?

Is this captive audience not going to switch providers for a 50% discount? Especially when the effort is simply swapping one URL for another?