well it's not due to price changes, 1 USDT = 1$, so yes there are less coins in circulation.
Poster below says Tether can create and destroy coins at will. They can certainly create them, not sure they can destroy them if in others wallets (and doing so would be a huge adverse news event). If they have destroyed coins can only be their own (in their own wallets) but I suspect that would also be transparent. My feeling is that yes there have been $10bn of redemptions.
No, it's not. Because that could be a possible motivation for tether to remove supply, to artificially increase the price again, to get close to peg. And as far as I understand, nothing in Tether is transparent, so I'm not sure if they can't just destroy their own tokens without someone being sure that this is happening.
Actually they most certainly can and have. The ERC20 contract for USDT has a blacklist function and the administrator can block transfers for arbitrary addresses, rendering it worthless. Same with USDC.
They can mint a quadrillion Tether today and that would do the job pretty well. The Tether would still be in the wallets, but at that point it would be quicker to just read from /dev/urandom if you wanted some random-ish bits.
Poster below says Tether can create and destroy coins at will. They can certainly create them, not sure they can destroy them if in others wallets (and doing so would be a huge adverse news event). If they have destroyed coins can only be their own (in their own wallets) but I suspect that would also be transparent. My feeling is that yes there have been $10bn of redemptions.