It is fixed at 21M but technically, this can be changed through an Economic Majority [0][1].
[0] https://en.bitcoin.it/wiki/Economic_majority
[1] https://bitcoin.stackexchange.com/questions/3945/how-could-t...
[0] https://en.bitcoin.it/wiki/Economic_majority
[1] https://bitcoin.stackexchange.com/questions/3945/how-could-t...
But then, this is where Bitcoin is genius: the code isn't everything.
There's a whole bunch of built-in economic incentive feedback loops.
And getting to an "Economic Majority" is very unlikely to happen because none of the participants have to gain from that change.
Also: since a bitcoin is divisible to 10e-8, it's going to be a very long while before there's an actual shortage of the darn thing.
Is the implication that monetary and fiscal policy also not driven by economic feedback loops? Of course they are; just different ones.
Any fork or decision by anyone to change this 21M number means that for me (and most hardcore bitcoiners I know) the chain which sticks to Satoshi's 21M becomes the REAL bitcoin chain.
21M is non negotiable. If it doesn't have 21M, it simply isn't BTC.