BIP 35, outlined in BIP-35, introduced a ‘mempool’ message that peers could send to a node to ask for a list of currently unconfirmed transactions. While conceptually useful, it never gained widespread adoption in everyday node communications.

Many nodes simply limit or disable direct mempool queries, focusing on more efficient or privacy-preserving protocols. As a result, BIP 35 is part of Bitcoin’s historical evolution of P2P message types—still valid, but overshadowed by newer, more robust ways of sharing transaction data.