There are no designations in the Altera® device part number that signifies if the device operates in the Extended Industrial temperature range.
Certain Industrial temperature range devices have been qualified for operation over the Extended Industrial temperature range at de-rated frequencies. These devices retain the Industrial temperature range marking "I" in the Operating Temperature field of the Ordering Part Number (OPN).
Note that only certain Industrial temperature range part numbers have been qualified for operation over the Extended Industrial temperature range.
These qualified devices will operate over the Extended Industrial temperature range as specified.
For more information go to the Extended Temperature Device Support page.