Antonym of “ephemeral” is:

The antonym of "ephemeral" is Lasting. The word "ephemeral" means lasting for a very short time, transient, or fleeting. It describes something that is short-lived or exists only briefly.

• Lasting is the correct antonym because it means continuing or enduring for a long time; permanent. It signifies longevity and permanence, directly opposing the short-lived nature of something ephemeral.
• Temporary is a synonym of ephemeral, meaning lasting for only a limited period.
• Fleeting is also a direct synonym of ephemeral, meaning passing quickly or rapidly.
• Brief is another synonym, meaning of short duration or extent.

The other options all convey the idea of shortness or transience, making them synonyms rather than antonyms of "ephemeral."