SCIFF v3 is a ground-up C++ rewrite of my Super Compact Image File Format, descended from the same core ideas as v1 and v2 but substantially redesigned. The encoder and decoder are dramatically faster than the earlier Python implementations, and the format's compression is now competitive with PNG and JPEG on nearly all image types — usually matching or exceeding both. It doesn't yet reach the compression levels of modern formats like WebP or AVIF, but for a hobby format it holds its own against the widely-deployed baselines. Files can still be converted to and from SCIFF, with metadata support carried over from earlier versions.