Looking at a 1 minute chart, it was on huge volume. Bigger than any single minute all day Friday and half of Thursday (as far back as minute chart will go)...
PS- volume for the whole first hour was 20,986 GC...which is pretty significant for a pre-market hour IMO. Only one other matching hour (18:00 ET) the entire month of June during this time period was close, 6/21 at 17,687. Every other matching time period is roughly around 2-3k volume.