MAX_ADDED_ENTRIES
The default cap on how many added peers a single PEX message carries, so a packet stays small. libtorrent uses max_peer_entries = 100 (ut_pex.cpp:61); this port caps at 50 per the session policy. dropped peers are not counted against this limit. Only newly-added ones count, matching if (num_added >= max_peer_entries) break; in ut_pex_plugin::tick.