The debt deal had at least 3 different tranches. I can't find details on how all the $13 Billion is structured (reminder: what I posted above is my best estimate. I'm hoping I was gonna get someone who knew these details better...)

I know that at least $3 Billion is fully unsecured (!!), no collateral involved at all. I forget what the other $10 Billion was like right now though. So its complicated.

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Elon Musk was responsible for the $33 Billion. $44 Billion buyout + some debt (I guess Twitter had $2 Billion preexisting debt?) == $46 Billion total buyout, structured as $13 Billion from Morgan Stanley + other banks, and $33 Billion from Elon Musk.

However Elon Musk raised "his end" of the $33 Billion is yet another mystery. He probably sold TSLA shares, or took a loan using TSLA stock as collateral. But this is independent of the $13 Billion I was talking about earlier.