Is GPT-5 using a new pretrained base, or is it the same as GPT-4.1?
Given the low cost of GPT-5, compared to the prices we saw with GPT-4.5, my hunch is that this new model is actually just a bunch of RL on top of their existing models + automatic switching between reasoning/non-reasoning.
GPT-5's knowledge cutoff is September 2024 so my first thought was they used GPT-4's pretrained base from 2024 and post-trained it additionally to squeeze those additional +5% on the benchmarks. And added the router.
