What key metrics and KPIs do you track for success with enterprise clients?

The only standard metrics or KPIs I can provide to you for tracking success with enterprise clients are meta metrics and meta KPIs: how do you measure the value of your product? All metrics and KPIs should focus on how a customer will know the ROI in your solution is worth it. Tracking activity metrics or touchpoints serves you to know your staff isn't lazy... but it does NOT measure success if you are looking at success as answering these questions: what value has the customer received? what organizational goals are supported by our solution? are we making our customer a hero or a zero in their role?

Personally I'm always a fan of holding CSMs accountable to a retention $ or % target, so that's always up there for me. I do also think that having an expansion component becomes more compelling for Enterprise CSMs as it is common to spend a lot of time working closely to help your customer achieve their business goals, which can naturally lead to an upsell.

From there, I'd think of 2 other things:
1) Relationship/customer journey based KPIs: I expect every Enterprise customer to get shown the value they're getting from your platform/service on a regular basis and I'd expect Executive engagement regularly too.
2) What are the leading indicators of retention or upsell? I want to see the health score of an Enterprise customer and I want to see things like which teams within this larger customer are adopting and getting value vs not.