MSNBC reporting it as 'confirmed'. No official statement as far as I can tell from the Campaign.
I know nothing about Gov Walz, he wasn't really on my radar. One good thing about choosing a Gov is that it doesn't impact the number of Dems in Congress.
Morning Joe reporting him as a 'moderate' Democrat. He's also a veteran and a former Congressman. Wiki shows him as age 60, which may appeal to voters looking at that sort of thing.
Minnesota is a MidWestern state so that's hopefully good as far as appealing to that Demographic. May also help with swing states Michigan & Wisconsin as they're all considered 'upper MidWest'.