The original message said the prize is "Bitcoin, in an amount equal to 1 million USD".
On April 13, 2019 the value of 1 BTC was $5,066.87 USD. That means the prize is 197 BTC.
The price of Bitcoin was lower for the previous 6 months, so its possible the prize is more than 197 BTC. For the sake of tracking the current value of the prize, we will stick with 197 BTC. There is a post on reddit containing what looks like a clue for the hunt from before March 7th, 2019. This would support the current prize value being even higher.
<!--I have hidden one thousand keys around the globe. Whoever unearths two hundred of them can combine them using the ancient magic of the wizard Shamir... and one million dollars of BTC will be theirs.-->
<!--Your first clue will appear here on the 7th of March, 2019 at 00:00 EST-->
On the opposite side, the prize could be interpreted as you get exactly $1M US in Bitcoin when you claim it. i.e. the prize value doesn't fluctuate with the market.
On thing is clear, until we find the public address for the Bitcoin wallet of the prize, nothing is clear !
See the Home Page for the current value of the prize.