The wider training squad gathered on Monday and two teams are entered in the event, playing as the GB Lions and GB Royals.
Each team features players from across the unions, with coaches Simon Amor and Gareth Williams considering a number of factors in their selection.
Team GB Sevens Head Coach Amor said: "It's been a very exciting first few days, the talent is exceptional and the way the guys have trained in the sessions shows real intent. They are bringing out the best in each other.
"We've put a big focus on the importance of an extraordinary GB spirit. The players have really embraced that and everyone knows we are on a unique and special journey together over the next seven weeks.
"There was a clear criteria for the two squads. Firstly, it was about the GB feel and making sure there was a good combination of the home nations in each team. Secondly, we wanted to look at certain combinations and specific positions.
"Heading into this first tournament, we also have some guys on limited game time as they return from injury, so someone like Cory Allen needs to be partnered in a squad with a player in the same position who can do a full 14 minutes. We need to manage players through this event as a three-week intense training block follows and we want them fresh for what will be a very competitive phase in our preparations.
"The rugby we've seen in the past few days has been of an incredibly high standard and we are looking forward to putting that out on the field in Moscow," he added. "Mistakes will be inevitable, given the limited time together, but we will have a very simple approach to attack and defence. The biggest thing we are looking for is that hunger and desire to work for each other and GB."
The GB Lions play Portugal, France and Poland on Saturday and the GB Royals face Georgia, Lithuania and Russia. To have a focused look at the players in a busy playing schedule, Amor will lead the Lions, with Williams in support, and vice versa for the Royals. The two coaches will then switch squads for day two.
Exeter (9-10 July) and Gdynia (16-17 July) are also part of the Grand Prix Series and for this season the GB Lions and GB Royals have taken the places of Wales and England. As a result Rugby Europe has stipulated that players cannot interchange between the two teams for the three competitions.
"The players named in the Royal and Lions must now remain in those sides for the three tournaments, which is a challenge for us," said Amor. "We have the advantage of Sevens and the City to mix the groups up but from what I've seen of training in the last few days it is evident that this will be our most competitive environment to test different combinations.
"As a programme we have overcome a lot of challenges in the last nine months by adapting well and with integrity. The ability to handle these situations will be a big positive for us come Rio. With sevens being in the Olympics for the first time there is much unknown for all the competing squads. It will be different to what everyone on the circuit is used to and these experiences will stand us in good stead for that."
GB Royals (Wales players in bold)
Cory Allen, Tom Bowen, Alex Davis, Jamie Farndale, Alex Gray, Warwick Lahmert, Ollie Lindsay-Hague, Ruaridh McConnochie, Luke Morgan, Scott Riddell, Joe Simpson, Luke Treharne (C)
Fixtures (all times in BST with a live stream available via www.rugbyeurope.tv)
9.28am v Georgia
12.28pm v Lithuania
3.28pm v Russia
GB Lions (Wales players in bold)
Mark Bennett, Dan Bibby, Phil Burgess, Sam Cross, James Davies, Richard de Carpentier, Lee Jones, Gavin Lowe, Tom Mitchell (C), Dan Norton, Mark Robertson, Marcus Watson
Fixtures (all times in BST with a live stream available via www.rugbyeurope.tv)
8.22am v Portugal
11am v France
2.22pm v Poland
