I just downloaded the version 0.16 and tried to generate a new address via GUI while syncing mainnet blocks. I have never activated multi-signature but it gave me an address starting with "3". As far as I know, segwit addresses currently start with "bc1q". Can someone tell me what's going on?
Not all addresses beginning with a
3 are multisig, and Bitcoin Core does not make you multisig addresses. Addresses beginning with a
3 are P2SH addresses. The segwit addresses Bitcoin Core generates by default are segwit scripts nested in a P2SH address in order to allow for backwards compatibility. If you want to use the native segwit addresses (bech32 addresses that begin with
bc1), you can start Bitcoin Core with
-addresstype=bech32 or go to the receive tab to get a new address and check the "Use bech32" checkbox.