MTG Salvation

How does Ancient Excavation's discarding effect and extra-draw effects such as Teferi's Ageless Insight interact?

1) Do I discard cards = to the # of cards in my hand at the time of casting AE, or
2) Since I draw double the cards, I also discard double?

If replacement effects change the number of cards drawn with Ancient Excavation, that will affect the number of cards "drawn this way". See also C.R. 614.6 and Read the Runes.

But compare Ancient Excavation with:

• Frantic Search or Varina, Lich Queen, where a specific number, "that much", or "that many" is used, rather than the number of cards "drawn this way". See also this thread. For the use of "that much" or "that many", see this thread and this thread.
• Jace, Mirror Mage or Sindbad, which have abilities that perform actions on a card after it's drawn. In this case, if an effect replaces the card draw, "the additional action is not performed on any cards that are drawn as a result of that replacement effect or any subsequent replacement effects" (C.R. 121.6). See also this submission on Reddit.

Thank you!