The date past which a model has no parametric knowledge. Libraries, APIs, and events from after the cutoff are fabrication traps unless their docs are loaded as contextual knowledge. Each model release ships with its own cutoff.
The cutoff exists because of how models are made: training bakes a snapshot of text into the model's parameters, and after that the parameters are frozen. The model doesn't know its knowledge has an edge — asked about something past the cutoff, it doesn't refuse, it extrapolates from the nearest thing it does know. That's what makes the trap quiet: code written against an old version of a library looks plausible, often compiles, and fails on the parts that changed.
The fix is always the same: get current information into context. Load the changelog, point at the installed version's type definitions, or have the agent read the docs from the web. Anything in context outranks nothing-in-parameters.
Usage:
"It keeps writing the v3 SDK syntax — we're on v5."
"v5 shipped after the knowledge cutoff. Load the v5 changelog as contextual knowledge, otherwise it'll keep fabricating from the older parametric version."