A custody level increase almost always triggers a facility change, and the reason is straightforward. Facilities are built and staffed to manage inmates at specific security levels. A level 2 inmate and a level 4 inmate have different supervision requirements, different housing needs, and different risk profiles. When someone's classification score moves up two levels, the facility they are in may no longer be appropriate for their new classification.
Whether a transfer happens immediately depends on one thing: whether Charles Center Prison has a separate housing division or unit that is designated for level 4 inmates. Some larger correctional complexes have multiple security levels within the same physical campus, with different units, different yards, and different staffing ratios for each level. If that is the case at Charles Center, your husband may simply be moved to a different unit within the same facility rather than transferred to an entirely different prison.
If Charles Center is a single-level facility built around level 2 classification, then a transfer to a facility that can properly house level 4 inmates is likely coming. The timing depends on bed space at the appropriate receiving facility and the transfer scheduling of the corrections department. It could happen within weeks or it could take a couple of months.
The custody level increase itself is worth understanding. Something triggered it, whether a disciplinary infraction, a reassessment of risk factors, or something that happened inside. Your husband speaking with his case manager about what drove the reclassification and what it would take to bring that level back down is a worthwhile conversation, particularly if the transfer would move him significantly farther from home.