1. I asked it a question about a feature that TypeScript doesn't have[1]. GPT4 usually does not recognize that it's impossible (I've tried asking it a bunch of times, it gets it right with like 50% probability) and hallucinates an answer. Gemini correctly says that it's impossible. The impressive thing was that it then linked to the open GitHub issue on the TS repo. I've never seen GPT4 produce a link, other than when it's in web-browsing mode, which I find to be slower and less accurate.
2. I asked it about Pixi.js v8, a new version of a library that is still in beta and was only posted online this October. GPT4 does not know it exists, which is what I expected. Gemini did know of its existence, and returned results much faster than GPT4 browsing the web. It did hallucinate some details, but it correctly got the headline features (WebGPU, new architecture, faster perf). Does Gemini have a date cutoff at all?
[1]: My prompt was: "How do i create a type alias in typescript local to a class?"