As an industry standard, it is recommended to get one ISBN for each format your book will be available in. This means if you are planning to release your book in multiple formats such as paperback, hardcover, e-book, and audiobook, you will need to obtain a separate ISBN for each edition.
By obtaining separate ISBNs for each format, you ensure that retailers have the necessary information to correctly list and sell your book in the appropriate formats. Additionally, having distinct ISBNs makes it easier for readers and buyers to identify and purchase the specific edition they desire.