Per the manual (page 83/84), it looks like you can get up to 50K points when saving to CSV. This can be changed in Settings > Length
"When saving to a CSV format file, the maximum number of data points is 50,000."
Looks like can get 100K points over USB | SCPI, but this would require some coding. More details on Page 627 of Programming Manual
"MAXimum or RAW will allow up to 100,000 points to be returned."