The most stable in exchange for what? Itself? So is everything else, idiot.
To claim its stable is to claim its stable in relation to something. In relation to what?
Huge claim to give zero examples c goods other than itself it is so stable against.
Discussion
No everything else is not stable against itself. Everything else's supply can be increased as everything else can be produced if market demands. Try producing more bitcoin.
Bitcoin's supply is not centrally planned, anyone can have their node/miner go beyond 21M and fork/branch off, but since good money requires absolute scarcity - market achieves the consensus to stay on 21M limit.