Is it possible to create, sign and broadcast a transaction with fee rate less than 1 sat/vbyte?
Yes, we can create, sign and broadcast transactions with fee rates below 1 sat/vbyte. However, it requires some workarounds and such transactions will most probably not be mined because most full nodes do not allow such transactions in their mempools.
minRelayTxFee is an option in the
bitcoin.conf file that can be used to change the fee rate required for mempool inclusion as explained by Murch.
These are the steps for broadcasting a low fee rate tx which I found in a reddit thread:
Pair HW wallet to Electrum
paytomanycommand to create a transaction with fee rate below 1 sat/vbyte
Import the transaction to sign in Electrum
Run a full node with
minrelaytxfeeset to 1 sat (0.001 sat/vB)
Find low-fee peers
addnodeto connect with the low-fee peers discovered
sendrawtransactionto broadcast transaction
Check tx in block explorer: https://sochain.com/
Related question: What is the smallest fee you can pay for an on chain transaction?
Related options in bitcoin.conf:
incrementalrelayfee : Fee rate (in BTC/kB) used to define cost of relay, used for mempool limiting and BIP 125 replacement.
dustrelayfee : Fee rate (in BTC/kB) used to defined dust, the value of an output such that it will cost about 1/3 of its value in fees at this fee rate to spend it.
You can "create, sign and broadcast a transaction with fee rate less than 1 sat/vbyte" but there is a minRelayTxFee set by default to be 1,000 satoshi per kB and a dustRelayFee defined here. So if you want your transaction to be relayed by nodes on the network you need to be careful not to drop the fee too low as not only will it not propagate across the network but it also won't end up in a mined block.