How Does a “Zero-Fee” Transaction Behave in the Mempool?

A zero-fee transaction, one with no fee or a fee below the network's minimum threshold, will generally be ignored or quickly dropped by most full nodes and miners/validators. Since block producers are economically incentivized by fees, a zero-fee transaction offers no reward and is not prioritized for inclusion.

It will likely remain unconfirmed unless the network is completely empty or a block producer chooses to include it altruistically.