Generally hearing both June 22 and June 23. Here’s some evidence to back up both dates, regardless you should check this account around 10AM PT on both of those days for good measure.
For June 22
-Last week’s documentation has June 29 date for Steam Machine user manual being released
-June 22 and June 29 are both Monday. Steam Controller was announced and released on Mondays a week apart.
For June 23
-Source told me review video embargo lifts June 23. Embargo for Steam Controller was April 27, was announced April 27.
-If announced June 23, a launch would be exactly a week later on June 30, the last day of June. This would keep Valve’s first half of the year promise while also being Summer.
1. Announcement for Hardware reservations and prices expected between Jun 22 - Jun 30
2. Reviewers are actively receiving Steam Machine and Steam Frame units (see enclosed photos)
3. Steam Machine comes with a Steam Controller, 2 mounting brackets and a Steam Machine in a box.
4. There are separate boxes for faceplates (unsure if shipping by default)
5. Creators embargo seems to be due to lift on Hardware reviews after Jun 23
6. Unclear whether Steam Machine and Frame are launching simultaneously, likely