More than 10% inflation for the next 10 years, more than 5% inflation for the next 25 years. This was made for the purpose of stability and to bring down volatility. Considering that grin might never have bitcoin's level of adoption in the next 10 years, grin's move will be predominantly on a low volatility line going down.
I reckon grin's development team were very serious when they said that this will not be a get rich quick coin.
Grin isn't for getting rich quick.
Source https://github.com/mimblewimble/docs/wiki/Monetary-Policy