Complex sentence: Many Americans consider "Biographie" to be the first half Petit climbed in 1996 and "Realization" to be the extension, whereas other climbers such as Adam Ondra and Sylvain Millet refer to the entire route as "Biographie".
Split into simpler sentences: Many Americans consider "Biographie" to be the first half Petit climbed in 1996; and "Realization" to be the extension. French climbers such as Sylvain Millet refer to the entire route as "Biographie".