Looking that the easy-rsa 3 script that now comes bundled with OpenVPN, that value is set to 2048 bits:

set_var EASYRSA_KEY_SIZE 2048

# gen-dh backend: gen_dh() { verify_pki_init

local out_file="$EASYRSA_PKI/dh.pem" "$EASYRSA_OPENSSL" dhparam -out "$out_file" $EASYRSA_KEY_SIZE || \ die "Failed to build DH params" notice "\

https://github.com/OpenVPN/easy-rsa/blob/master/easyrsa3/eas...