SPV wallets only download block headers—80 bytes per block—and request Merkle proofs from full nodes for transactions they care about. The wallet can confirm a transaction’s inclusion in a block by checking the Merkle path to the block’s root hash. While more bandwidth-efficient and requiring less storage, SPV has privacy trade-offs: full nodes see which addresses or TXIDs you’re querying. Newer methods like Neutrino (BIP 157/158) improve privacy by letting clients fetch compact filters. Still, SPV depends on honest nodes relaying valid headers and proofs, so it’s slightly less trustless than running a full node.