Updated short interest:
15,139,641 shares, $15.002B at risk.
Ihor's estimate was 16.17M shares, 6.81% too high.
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All of this below is assuming that you don't have margin enabled.
Buying options with cash never uses anything as collateral. You are
buying the options, they're yours to sell, exercise, or let expire. (There are delta hedging effects, of course, but this doesn't affect the ownership/lending status of your stock, other than its value.)
Selling options does use collateral. If you sell a put option, 100x the strike price in
cash (that is, what you would owe if the option were to be exercised) will be held as collateral. The only way that
stock is held as collateral is if you sell a
call option, in which case 100 shares of the underlying stock will be held as collateral (and presumably that's where lending may come in). Note that you can't sell a naked call (which has unlimited loss potential, just like actually shorting the stock) without margin, because of this - without margin you must have the actual stock to be held as collateral.
And then spreads are another thing.
In all cases, the long leg of the spread acts as protection against the short leg getting exercised.
In a debit spread (where the long leg's strike price is closer to the current price and is therefore more valuable), the maximum loss is what you paid for the spread, so no collateral is held, you own the spread (but you can't sell the long leg of the spread without having collateral for the short leg, replacing it with another long leg in the same order, or buying back the short leg in the same order!) If the short leg were to somehow get exercised, the long leg guarantees
profits even, of 100x the difference between the strike prices.
In a credit spread, the maximum loss is if the short leg (more valuable) gets exercised, causing you to have to exercise the long leg - therefore it's 100x the difference between the strike prices - and that is the cash collateral that must be held. (Note that even in a call credit spread, where the short leg would normally mean unlimited loss potential, the long leg limits the loss, and therefore only cash needs to be held as collateral, not stock.)