Sebastian Siemiatkowski doesn’t look like a banker. The Klarna CEO dresses more like a tech bro, which is befitting as his company straddles the world of finance and technology. He rushes into our early morning interview, bespectacled and in jeans, a T-shirt, a navy button-up and white sneakers, the shoes high-end ones by the French fashion house Céline. He tells me he was up late “vibe coding”—coding by “feel” using a large language model like ChatGPT (Siemiatkowski is friends with OpenAI boss