In stanza 1 of "Ode on a Grecian Urn", what literary device does the speaker use to speak directly to the urn?apostrophe

This poem starts with personification.  Personificiation is the literary device in which an author acts as if an inanimate object is actually alive.  To put it more formally, personification is a figure of speech in which an inanimate object is imbued with human characteristics or is addressed as an animate being.

You can see Keats do this right away in the first line.  He addresses the urn as "thou" and calls it a bride and a child and a historian.  Obviously, the urn is none of these things, it is just a pot.

So, by talking to the urn as if it were a person, Keats is using personification.