Answer: Ascaris lumbricoides
Although we don't have the worms to examine in this case, the presence of multiple large tan-white worms with a smooth outer cuticle within the lumen of the intestine is strongly consistent with A. lumbricoides. The female A. lumbricoides can get quite large, reaching lengths of 35 cm!
One reader also raised the possibility of anisakiasis given that these worms were found on an upper endoscopy. However, the large size would exclude anisakid larvae given that they only reach a few centimeters in length. Also, the presence of multiple worms would be unlikely for anisakiasis, since usually only 1 larva is seen in these cases. Finally, anisakids try to recapitulate their lifecycle in their marine mammal host and embed into the gastric or intestinal mucosa. This type of behavior was not seen in this case.