Huh. I didn't notice Claude had serif font. Now that I look at it, it's actually mixed. UI elements and user messages are sans serif, chat title and assistant messages are serif.
What an "odd" combination by traditional design standard practices, but surprisingly natural looking on a monitor.
This is basically why I went with serif for body text in our branding. The particularly "soulless" parts of tech are all sans-serif.
Of course, that's just branding and it doesn't actually mean a damn thing.