There are five fard (obligatory) prayers in Sunni Islam:
You have to offer perfectly the five compulsory prayers in a day and night (24 hours), unless you want to pray Nawafil.
Sahih al-Bukhari 1891
This hadith confirms that night prayers (witr) are voluntary:
... the most excellent prayer after what is prescribed is prayer during the night.
Sahih Muslim 1163 a
In the Hanafi madhhab, night prayerswitr (among other prayers) are considered sunnah muakkadah (SeekersHub), which is defined as:
It is that Sunnah which [Prophet Muhammad] and the [Companions of the Prophet] had done with continuity or had emphasized it and leaving this Sunnah without a valid reason will lead to committing a sin and this person will be deprived of [Prophet Muhammad's] intercession on the day of [resurrection].
efiqh.com
So witr is considered wajib (necessary; essential) by Hanafis. Consequently, Hanafis may consider the sunnah muakkadah prayers as virtually obligatory.