There is no fixed minimum cluster size at which internal links suddenly start creating authority, and any specific node count you have seen is invented, because authority does not switch on at a number. Internal links build authority by expressing real topical relationships, helping pages get discovered and crawled, and distributing relevance and link signal across a coherent set, and that effect grows with how completely you cover the topic’s core questions, not with how many nodes you can count. The honest reframe is to stop asking for a minimum size and start asking whether the core sub-questions are covered and linked.
The reason no threshold exists is that the value of internal links depends entirely on what they connect. A handful of pages that each answer a genuine core question, linked together because they are truly related, can pass meaningful signal and read as a coherent body of coverage. A larger set of loosely related or thin pages, linked merely to hit some imagined count, passes little, because the links describe relationships that are not really there. Two clusters of the same size can behave completely differently, which is why a number divorced from coverage tells you nothing useful.
It is worth holding the uncertainty plainly rather than smoothing it over. How internal links contribute to authority is also bound up with whether the linked pages actually rank and get cited, which depends on the strength of each page and the topic’s competitiveness, not on the link structure alone. So even a well-linked cluster has no guaranteed point at which authority appears on schedule. The truthful position is that the mechanism is real but the timing and exact size are genuinely uncertain, and a manufactured minimum would only hide that.
What you can act on is coverage of the core. The internal links earn their keep when they connect pages that together answer the central questions of the topic, because then the links map real relationships that aid discovery and concentrate relevance where it belongs. Build to that, not to a count.
So instead of aiming for a minimum number of pages before linking, identify the topic’s core sub-questions, build pages that genuinely cover them, and link them according to their real relationships. Let the cluster grow until the core is covered and connected, and judge it by coverage and coherence rather than by node count.