However, it is more common to measure inflation by the increase in nominal prices of goods, as I did above with gold. And, by this measure, Bitcoin is deflating. It's hard to measure the deflation rate with precision because it's so volatile, but at the beginning of 2011, it was worth 10¢, and now it's US$6600. It's oscillated wildly around the exponential trend line by about a factor of 3 on each side, but the trend line itself is a deflation by about 75% per year (or of 300% per year, if you look at deflation that way.)
Presumably this won't continue forever, as it's more appropriate to tulip bulbs than to a usable currency, but it is certainly quite far from inflation in the usual sense.
The vast majority of the supply is owned by a very small oligarch.
The chances of Bitcoin becoming obsolete or failing catastrphically due to a glitch or bug in the protocol software - like what just happened a few days ago (luckily by someone who desired to fix it, if the bug was found by a malicious actor they would have destroyed the entire Bitcoin ecosystem), the cryptocoin software can not be guaranteed as a safe store of value.
Anyone who "invested" in Bitcoin at the start of this year has lost upwards of 50%, so that would qualify as inflation in your terms. Other cryptocoins have seen losses exceeding 80%-90%.
The way cryptocoins work is by early users dumping their supply onto new users to exit and extract real value from the suckers who then become bag holders, the new users hope to do the same but are at a severe disadvantage to early users who own the vast majority of the supply.
Early in Bitcoin history, by design Bitcoin went though a period of hyperinflation where Satoshi and a few users acquired most of the coins in circulation.
Aprox 4.11% of Bitcoin users (addresses) control 96.53% of all bitcoins in circulation.
Also there's a chance that something will make Bitcoin obsolete in the near future - immediately destroying the trade value of Bitcoin, either a new cryptocurrency, a quantum computer or cryptographic breakthrough that would allow theft of BTC private keys or more predictably a bug like what recently happened in the main Bitcoin core wallet client software which allowed a user to inflate the supply of Bitcoins past 21 million and mint more BTC for free.
So if you were truly concerned about long term stability - gold or tangible functional assets would be much safer than software based pet rocks.
https://www.livebitcoinnews.com/cve-2018-17144-the-aftermath...
Quite a concerning catastrophe that has no guarantee of being avoided in the future, as any programer knows how many bugs can hide or be exploited in any code base.