There’s no animation built-in currently. But it’s fast enough that you can often just throw away and re-render the Plot (i.e. handle the animation externally).

Mike Freeman made a helper function that adds that sort of animation (data gradually coming in) using D3 atop Plot: https://observablehq.com/@mkfreeman/plot-animation

You could upvote this incremental rendering issue: https://github.com/observablehq/plot/issues/328

Or this one for adding a “time channel” to do data-driven animation (for which there’s an old draft PR): https://github.com/observablehq/plot/issues/166