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Is it possible to create, sign and broadcast a transaction with fee rate less than 1 sat/vbyte?

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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.

minRelayTxFee-conf

These are the steps for broadcasting a low fee rate tx which I found in a reddit thread:

  1. Pair HW wallet to Electrum

  2. Use the paytomany command to create a transaction with fee rate below 1 sat/vbyte

  3. Import the transaction to sign in Electrum

  4. Run a full node with minrelaytxfee set to 1 sat (0.001 sat/vB)

  5. Find low-fee peers

  6. addnode to connect with the low-fee peers discovered

  7. sendrawtransaction to broadcast transaction

  8. Check tx in block explorer: https://sochain.com/

Related PRs:

https://github.com/bitcoin/bitcoin/pull/13922

https://github.com/bitcoin/bitcoin/pull/13990

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.

related-options

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  • This answer could be improved by giving an explanation in the introduction what one is looking at. I would suggest you add something at the top along the lines of "yes, it is possible to use a lower fee rate. <how does that affect relay, confirmation, other tradeoffs>, then: here is one way I found to do it:". – Murch Oct 18 '20 at 13:37
  • @Murch made some changes – Prayank Oct 19 '20 at 11:18
  • Good improvement! I've condensed it a bit by paraphrasing the question in the answer, and removing the quotes. Please feel free to roll back or edit further, if you liked the original better. – Murch Oct 19 '20 at 13:49
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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.

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  • This answer could be improved by being more explicit about the limit that should not be undershot for "not to drop the fee too low". – Murch Oct 19 '20 at 22:54

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