In an IGN interview the executive producer of Valorant, Anna Donlon, has revealed some interesting things about agents when the game comes out.
"Of the ten or so agents available at Valorant’s launch, five will be fully unlocked out of the gate. From there, players can unlock additional characters.”
For the other five agents to be unlocked, it looks like each player will have to win them through an 'engagement-incentivized model.'
We can assume that Valorant's battle pass — which will be free — could allow you to earn them as in-game rewards. All you'll have to do is play. For those who don't have the time, or don't want to wait, they'll also be available for purchase.
Please note that in-game purchases won't provide you with gameplay advantages or bonus. You can be reassured, the game won't be pay to win.
We don't have any information at this time about an official release date. Valorant will be launched in Summer 2020, but we can assume a beta phase will take place before that.