A user on ResetEra was able to find a FAQ and list of participating companies that showed the current attendees of E3 2020.
At the time of publishing, the following studios will be appearing:
- Activision Publishing, Inc.
- Amazon Game Studios
- BANDAI NAMCO Entertainment America Inc.
- Bethesda
- Capcom USA, Inc.
- Epic Games Inc.
- Kalypso Media Group
- NCSOFT
- RDS Industries Inc.
- SEGA
- Square Enix, Inc.
- Take-Two
- TENCENT
- THQ Nordic
- Ubisoft Entertainment SA
- UnnamedVR by Paracosma
- Warner Bros Interactive Entertainment
- XSEED Games
