All exports in Spotfire done from the visualizations will go through formatting, and the default behavior of string formatting is to truncate very long strings. This means that all table cells that are exported to CSV will be truncated after 65535 characters.

The normal API export also use the default string formatter and truncate the exported values.

DataTable table;
DataValueCursor<int> cursor1 = DataValueCursor.Create<int>(table.Columns["Column1"]);
DataValueCursor<double> cursor2 = DataValueCursor.CreateNumeric(table.Columns["Column2"]);
DataValueCursor<string> cursor3 = DataValueCursor.CreateFormatted(table.Columns["Column3"]);
DataSelection selection;

foreach (DataRow row in table.GetRows(selection, cursor1, cursor2, cursor3)) 
{
  int rowIndex = row.Index;
  int value1 = cursor1.CurrentValue;
  double value2 = cursor2.CurrentValue;
  string value3 = cursor3.CurrentValue;
  DoSomething(rowIndex, value1, value2, value3);
}