I've submitted my German taxes this year using a mix of Claude 4.6 and Claude 4.7, with lots of manual checking. The German Finanzamt granted most of the things I listed in the tax return (they send you an official letter by post) -- I did have to appeal for one of the items though (again using Claude, this time 4.8 ).

The most important thing I've found is to ask Claude to thoroughly audit the reply (to find all hallucinations). I usually ask it to give me an enumerated list of all facts and all legal cases quoted, and then I give it to a new instance to carefully validate each one.

Newer models are getting much better at not hallucinating German case law though :)