Next Best Action
The interaction. As the user takes action in-session, the system evaluates the event against recent history (this session and prior days) and recommends the next-best action — surfacing content, offer, or guidance.
Why it lands at Intra-session latency. The decision needs context that a single attribute lookup can't provide; it requires streaming evaluation across multiple events or a stochastic prediction. That puts the latency floor at ~10 seconds and the ceiling at a few minutes (source.real-time-clarity-md).
Why it's expensive. Increasing data and processing power applied to the decision raises cost-to-deliver exponentially with target latency. NBA at Intra-session is order-of-magnitude cheaper than NBA pushed up to Inter-page.
Architectural implications. Requires streaming infrastructure (Kafka/Pulsar/Pub-Sub class), a real-time feature store, and a decisioning service capable of low-millisecond inference. Composable stacks can deliver this; packaged CDPs offering it ship it as a higher-tier SKU.