The San Francisco 49ers offseason workout program is set to begin its first of two minicamps on Tuesday. All NFL teams have a mandatory minicamp in June (49ers is set for June 9-11). Due to Jim Tomsula's promotion into the head coach role, the 49ers are also allowed to have a voluntary minicamp in April. It will take place April 28 through April 30. As Eric Reid pointed out, the team held physicals today, and things will get going on Tuesday.
The voluntary minicamp will fall under the guise of Phase 2 of the offseason workout program. Here is how the CBA describes the second phase in Article 21, Section 2, subsection b(ii).
Phase Two shall consist of the next three weeks of the Club's offseason workout program. Subject to the additional rules set forth in Section 5 of this Article, during Phase Two all coaches shall be allowed on the field. On-field workouts may include individual player instruction and drills, as well as "perfect play" drills (e.g., offense or defense only, but not offense vs. defense), or special teams drills on a "separates" basis (e.g.., kicking team or return team only, but not kicking team vs. return team). No live contact or team offense vs. team defense drills are permitted. No offense vs. defense drills are permitted (e.g.., no one-on-one offensive linemen vs. defensive linemen pass rush or pass protection drills, no wide receivers vs. defensive backs bump- and-run drills, and no one-on-one special teams drills involving both offense and defense are permitted.) Players cannot wear helmets during Phase Two.
There is no word yet on media availability. The team is getting ready for the draft this week, so I'd imagine the PR department might be just a little bit busy in advance of the three days of insanity.