Capability Drift Window

Frontier assistants change month to month, so any agency capability claim has a shelf life measured in weeks, not quarters. The Capability Drift Window is the gap between when a model ships and when your client-facing promises stop matching what the tool actually does. Agencies that treat model releases as procurement events (buy once, standardise, move on) accumulate silent drift: the retainer scope describes work the assistant could do six months ago, while competitors quote the current ceiling. The fix is a scheduled re-scoping cadence tied to release events, not annual reviews. When Anthropic shipped Claude 5.5 in September 2026, the practical question for agencies was not whether to switch, but which existing deliverables could now be quoted at a higher margin or lower hour count. Forrester's Q3 2026 research puts workflow integration, not model capability, as the bottleneck, which means drift shows up in delivery process before it shows up in output quality.