Which ancient Mesopotamian epic features Utnapishtim's flood vessel, a parallel to Noah's Ark?

The Epic of Gilgamesh features Utnapishtim’s flood vessel, a parallel to Noah’s Ark.

In the flood story within the Epic of Gilgamesh, the god Ea warns Utnapishtim to build a boat and preserve living creatures, family members, and skilled workers. Utnapishtim later releases birds to determine whether the floodwaters have receded. These motifs closely resemble elements of the Genesis account, including a warning, a survival vessel, preservation of life, and bird tests.

The Gilgamesh epic is preserved on clay tablets from ancient Mesopotamia and is associated especially with the first millennium BCE copies from the library of Ashurbanipal, although the underlying traditions are older. Its flood narrative also has important connections with the earlier Mesopotamian Atrahasis tradition.

The answer is not “the Epic of Atrahasis,” even though Atrahasis contains an older and closely related flood story. Utnapishtim is the survivor in the Gilgamesh version; Atrahasis is the survivor in the separate Atrahasis epic. That distinction makes the title asked for here specific.