Block from U+1F00 to U+1FFF. This block was introduced in Unicode version 1.1 (1993). It contains 233 codepoints.
The Wikipedia provides the following information on block Greek Extended:
Greek Extended is a Unicode block containing the accented vowels necessary for writing polytonic Greek. The regular, unaccented Greek characters can be found in the Greek and Coptic (Unicode block). Greek Extended was encoded in version 1.1 of the Unicode Standard as is, having had no additions up to 6.2. As an alternative to Greek Extended, combining characters can be used to represent the tones and breath marks of polytonic Greek.