Is Go! Saitama hentai?
No
Rated PG-13 (Teens 13 or older) on MyAnimeList and not tagged as Hentai.

ONA · 2021 · 1 episodes · PG-13 - Teens 13 or older
Comedy, Super Power
The short follows Saitama after he discovers a 1-yen (about US$0.01) sale for high-grade hot-pot meat — but the sale ends at 5:00 p.m. that day. (Source: ANN)
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