"The 400m hurdles provided me with unforgettable moments and shaped me into the athlete I am today," Bol wrote on her Instagram account on Friday.
"But I want to challenge myself again and push my boundaries," she explained.
"The 800m is new and unfamiliar territory, and that's precisely what makes it so interesting."
The 25-year-old, who retained her world title in Tokyo last month, made the decision to switch with her coach Laurent Meuwly.
The Tokyo triumph marked the end of another successful season for Bol, who completed an incredible sixth Diamond League campaign unbeaten.
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