Axios AI+

GPT-4.5, OpenAI’s big new model, represents a significant step forward for AI’s industry leader. It could also be the end of an era.

The big picture: 4.5 is “a giant, expensive model,” as OpenAI CEO Sam Altman put it. The company has also described it as “our last non-chain-of-thought model,” meaning — unlike the newer “reasoning” models — it doesn’t take its time to respond or share its “thinking” process.

Why it matters: The pure bigger-is-better approach to model pre-training now faces enormous costs, dwindling availability of good data and diminishing returns — which is why the industry has begun exploring different roads to continuing to improve each new AI generation.

Between the lines: Building and powering the massive data centers required to build and run the latest models has become an enormous burden, while assembling ever-bigger datasets has become challenging, since today’s models already use nearly all the data available on the public internet.