There needs to be a full sized (2/0 in this case) ground in every conduit of a parallel set.
This appears to be a supply side bonding jumper and, unlike an EGC, only needs to be sized for the ungrounded conductors that it is installed with.
In this case a 2AWG supply side bonding jumper in each raceway, on the line side of the 800 amp OCPD, assuming that is 3 raceway installation. It will need a 1/0 equipment grounding conductor in each raceway on the load side of the OCPD.
This exact layout really points out how flawed the code is in this area. The worst case, in my opinion, are the conductors on the line side of the OCPD, and we only need a 2 AWG in each raceway, but on the load side of the 800 amp OCPD, we need a 1/0 in each raceway.