Hi there, overall all partners, expert or otherwise, are expected to have a demonstrated track record serving clients in specific industries and topics (as opposed to non partners roles like associates or new EMs who are expected to be able to serve clients in any industry or topic to a certain degree). 

Having said that, there are 3 differences between expert partners and general partners from my personal observations:

1. Depth of domain expertise: Expert partners are expected to have global ‘pull’ i.e., they should be seen as the ‘go to gurus’ for the topics they are expert in for client teams around the world. Partners on the generalist track should know ‘something about something’ but not to the level that expert partners are expected to. 

2. Level of client leadership: Partners on generalist track are expected to have much greater client leadership in terms of finding new opportunities (and topics) to serve existing and new clients across a variety of topics. In my previous firm, this is seen as client leadership although others might define it as ‘selling projects’ but there was no formal revenue KPIs for partners in my firm. Expert partners are expected to maintain and grow relationships with clients but not to the extent of what is expected of a partner on the generalist track

3. Track towards senior partnership: It is very rare (although this may already be changing) for an expert partner to make senior partner as the bar on client leadership is on a global scale. Even ‘Master Experts’ on a pure expert track even more specialist than Expert Partners are mapped to Partner level (Senior Expert == AP, Master Expert == Partner). Far more common to see partners on the generalist track make Senior Partner (although this still requires significant work/luck to be sure)

Hope this is helpful. Quick caveat here that others may have differing views as this might change depending on the firm involved. 

Cheers

(editiert)