<p>BIP141 only requires a commitment to the witness tree to be present when there is at least one segwit transaction (= a transaction that spends a witness output) in the block.</p>

<p>This means that old miners in theory can keep working after segwit activates, as long as they don't include segwit transactions (easy, as they are nonstandard to them) and don't build on top of invalid blocks (harder, as it requires an updated full node).</p>

CC BY-SA 3.0
2017-03-24T17:34:29.250Z
I'm playing with this in `regtest` mode, but I'm seeing a SW commitment in an empty block. `getblock`: http://pastebin.com/eDeXGHEx and `gettransaction` of the coinbase tx: http://pastebin.com/3DxSFArc The block has an extra 36 bytes (size - stripped size) and the coinbase tx has an `OP_RETURN aa21a9ed...` Is it counting the coinbase tx itself as a SW tx? Making the whole block SW?
pinhead
CC BY-SA 3.0
2016-11-03T16:23:09.407Z
2016-11-03T16:23:09.407Z
Pieter Wuille
<p>Also, would that block's Coinbase contain some kind of empty witness commitment?</p>

<segregated-witness><witness-commitment>
If a block contains no SegWit transactions, does a miner send an (empty) witness?
pinhead
# If a block contains no SegWit transactions, does a miner send an (empty) witness?

(Asked by: username_0 on 2016-11-01)

Also, would that block's Coinbase contain some kind of empty witness commitment?

**Tags:** segregated-witness, witness-commitment


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## 1 answers

### Answer by username_1 on 2016-11-03. Score: 2 | Accepted answer

BIP141 only requires a commitment to the witness tree to be present when there is at least one segwit transaction (= a transaction that spends a witness output) in the block.

This means that old miners in theory can keep working after segwit activates, as long as they don't include segwit transactions (easy, as they are nonstandard to them) and don't build on top of invalid blocks (harder, as it requires an updated full node).

> **Comments:**
> **username_0**: I'm playing with this in `regtest` mode, but I'm seeing a SW commitment in an empty block. `getblock`: http://pastebin.com/eDeXGHEx and `gettransaction` of the coinbase tx: http://pastebin.com/3DxSFArc The block has an extra 36 bytes (size - stripped size) and the coinbase tx has an `OP_RETURN aa21a9ed...` Is it counting the coinbase tx itself as a SW tx? Making the whole block SW?  

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