It wasn't a surprise because bitcoin was close to $50k price for a couple of weeks but will it be stable there ?
During the next week will the price be heading downward because of sellers making profits or is it going upward when the next price to generate media interest will be $75k ?
It's difficult work out if it's going to stay stable at $48k to $50k
It is sustainable because every day big corporations are announcing support or adoption.
Here is one of the interesting articles on the subject:
Morgan Stanley: Cryptocurrencies Here to Stay as Serious Asset Class, Bitcoin Making Progress to Replace Dollar
https://news.bitcoin.com/morgan-stanley-cryptocurrencies-asset-class-bitcoin-replace-dollar/We may see some drops, but the price should rise in the long run.