How to set a default timestamp_ms for sqlite

How do I make a default timestamp_ms?

createdAt: integer("createdAt", {
      mode: "timestamp_ms",
    })
      .notNull().default( // what goes in here )

createdAt: integer("createdAt", {
      mode: "timestamp_ms",
    })
      .notNull().default( // what goes in here )

createdAt: integer("createdAt", {
      mode: "timestamp_ms",
    })
      .notNull().default( // what goes in here )

createdAt: integer("createdAt", {
      mode: "timestamp_ms",
    })
      .notNull().default( // what goes in here )