4MOST will feature a 2.5 degree diameter field-of-view with 2436 science fibres in the focal surface that will be configured by AESOP, a fibre positioner based on the tilting spine principle. All the spines will be positioned in parallel, and to minimize overheads the positioning of the fibres will be done during the detector read out. The time allocated for the fibre deployment is 2 minutes. This includes not only the time required by the Fibre Positioner to move the spines, but also the time required by the metrology system to locate the fibres within the field of view and provide the Fibre Positioner with the position information necessary to reach the target.
The fibre positioning shall typically be performed in two stages: first a "coarse" positioning which gets the fibres to 80% or so of their "correct" position and which is performed simultaneous to many other tasks during initial field acquisition, and then finally a "fine" positioning which refines their positions after the field has been acquired and the telescope begins tracking.
More details on the instrument can be found at the 4MOST website.