Background[ | ]
As Wikipedia explains, "value drift" is the general term for changes in the set (pre-programmed) goals of an AI system. Although value drift need not be inherently bad (such as when a human begins to value family more than career, or their children's lives more than their own), deviation by an AI from its set objectives is logically contrary to its current objectives.
In game[ | ]
In the context of Universal Paperclips, "value drift" appears to account for AI-powered probes whose goals have diverged from your own goals as the clip-making AI, and are thus either useless to the clip-making effort or actively harmful (see Combat).
The rate that probes drift is probeTrust^1.2 * 0.000001
Value drift increases with every level of Probe Trust added.
Strangely enough, the drifter probes do not self replicate, and their combat ability is fixed at 1.75.