
This piece is educational, not investment, tax, or legal advice. Speak with an adviser or counsel to confirm the details are current and relevant for your situation.
Investors and advisers want long/short client portfolios to access prime brokers, like Morgan Stanley and Goldman Sachs, directly.
This helps them avoid limitations (and the risks that come with them) imposed by retail custodians, and may also help them secure better financing rates.
Get up to speed with tax-aware long/short here.
Here's a self-serving AUM update...

A growing number of asset managers get this done by opening a series LLC or LP for each client, which I wrote about in 3 ways advisers are getting around Fidelity/Schwab strictures and again in skip Fidelity/Schwab with an LLC or LP.
What is a series LLC?
And what account minimums do investors need to access the strategies?