This links to the Mesa roster, which features the Pirates players. You can check the other rosters through the "teams" section at the top.
For whatever reason, the Pirates have only announced Robbie Grossman and Brock Holt so far. I believe every other major league team has announced at least four players. The Mesa team is also really short on the roster compared to other teams, with only 10 pitchers and 12 position players. Every other team has at least 13 pitchers and 13 position players.
Expect more Pirates players, especially pitchers, to be added soon. I expect Gerrit Cole to be one of them, but that's still up in the air.