[akashshah87]

Yes, donating stock means you avoid capital gains. But even more relevant in this case is that she likely inherited the Berkshire stock from her husband which also resets the cost basis which means she wouldn't have had to pay capital gains even if she had sold the portfolio instead of donating.

[Scoundreller]

I don't know enough about US tax law, but I think it's more likely the donation was somehow done without triggering a huge capital gains tax bill. We're talking about a nonagenarian billionaire that founded an investment house.

Their death could be no surprise and the accountants/lawyers on speed deal would be limitless.

Surely they had their books in order, unless they wanted to pay tax.