Flux or a permanent marker can be used to inform you of the metals temperature. Unlike sheet there is no center area to place the flux or mark. With wire, draw marks along the metal with a permanent marker, as shown in the above photo.
Heat the wire evenly and slowly by holding the torch high away from the metal circling over the wire heating it up. Then lower the torch flame closer to the wire and move very slow and watch the marks fade away as you move the torch.
You will see the wire relax and slump as its annealed.
Be careful not to move too slowly or you risk melting the wire, especially thin wire.