Google changes this often and I'm having a hard time finding it in the GA documentation.
What are the limits for custom variables and advanced segments?
Are they specified at the account, property, or profile levels in Google Analytics?
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The limitations to your question are as follows:
The total combined length of any custom variable name and value may not exceed 128 characters.
Note: Google Analytics Premium accounts have 50 custom variables available.
I’ve found that I can only create 100 advanced segments at a time. That may sound like a lot, but when you have more than a few Google Analytics accounts, it’s easy to start creating a lot of segments for yourself.
I hope this answers your question completely. Best wishes!
Take a look at this - Google Analytics Limits. I work as a technical analyst at an analytics agency and this is something very similar to what we use as reference.
Custom Variable Slots