It's a sequential/series setup. there's one small and one larger turbo. Exhaust port in between them. Until 4k rpm, smaller turbo builds boost (there's actually not a lot of lag, it starts spooling ~1500-2000rpm) to max of 10psi. At 4k, ECU drops the boost to 8psi, turns on the bigger turbo, both run at 8psi for a short time, and then the smaller turbo is turned off and the bigger turbo takes over past 4k rpm.
I couldn't use them because they won't clear the frame rail. So I have a t04s