Svelte 3 was released 4 years ago. Svelte 4 had VERY few breaking changes, and those were in obscure corner cases.
Four years in the JavaScript ecosystem denotes a very stable API. 99.9% of all Svelte 3 projects would likely need no code changes at all moving to v4, at least that's been my experience.
Four years in the JavaScript ecosystem denotes a very stable API. 99.9% of all Svelte 3 projects would likely need no code changes at all moving to v4, at least that's been my experience.