APPLE INSIDER
Apple has reportedly stopped production of the 512 gigabyte and 1 terabyte flash media configurations of the 21.5-inch iMac, which may signify an update is coming sooner rather than later.
Credit: AppleLong-time AppleInsider sources familiar with Apple’s supply chain have told us that Apple has stopped producing the 512GB and 1TB SSD configurations of the iMac 4K. Additionally, both models are newly listed as “currently unavailable” on Apple’s website. The 256GB SSD model and the 1TB Fusion Drive model remain available for purchase as of writing, albeit with some lead time.
Source: APPLE INSIDER