Internal 512 Bytes for the LPC55S Variants (Nitrokey 3A/C NFC) and 256 Bytes for the nRF52 Variant (Nitrokey 3 Mini). On the external flash these are 4kB blocks. Although space matters, usually no free blocks translates to: Nothing can be added to the storage anymore. In the future we will also show how many items there will be left to save for the various functionalities (Resident Keys for FIDO2, Secrets entries, ...)