The same number as on the original AR8200. 1000 memory channels in 20 banks. The banks are paired and can be set to have different sizes.
Bank A 40 channels and bank a 60 channels
Bank B 200 channels and bank b 80 channels
Each pair has 100 channels in total with an individual bank having between 10 and 90 allocated.
If the memory expansion card is used you can effectively have a further 4 sets of 20 banks BUT only any one set can be active in the scanner at a time. To activate one of the extra banks it has to be copied to the radio (and if you don't want to overwrite the ones in the radio you need to keep one of the 4 extra sets free to copy these to ).
All this information (and in much more detail) is easily found via webcrawler/google on the AOR UK and US websites.