Block from U+F900 to U+FAFF. This block was introduced in Unicode version 1.1 (1993). It contains 472 codepoints.
The Wikipedia provides the following information on block CJK Compatibility Ideographs:
CJK Compatibility Ideographs is a Unicode block containing Han Ideographs that contained duplicate characters in the South Korean KS X 1001:1998 (U+F900-U+FA0B), Taiwanese Big5 (U+FA0C-U+FA0D), Japanese IBM 32 (CP932 variant; U+FA0E-U+FA2D), JIS X 0213 (U+FA30-U+FA6A), ARIB STD-B24 (U+FA6B-U+FA6D) and the North Korean KPS 10721-2000 (U+FA70-U+FAD9) source standards for CJK characters. In order to retain round-trip compatibility with that standard, the CJK Compatibility Ideographs block was created to hold those extra characters. In subsequent versions of the standard, more compatibility ideographs, and even a few regular ideographs that do not have duplicates, have been added to the block.