<p>Backwards compatibility of Bitcoin forks depends solely on whether unupgraded nodes reject blocks that are valid under the new rules. If they do, it's a hard fork, if not, it's a soft fork.</p>
<p>SegWit is a soft fork because SegWit outputs are spendable by anyone under pre-SegWit rules, which means there cannot be a transaction that's accepted by SegWit nodes but rejected by pre-SegWit nodes.</p>

CC BY-SA 4.0
2024-09-27T06:35:45.810Z
2024-09-27T06:35:45.810Z
Vojtěch Strnad
<p>my question is in relation to SegWit backwards compatibility.</p>
<p>Based on the way SegWit script is constructed, just 0 and a public key, makes it spendable by anyone. The only thing that stops it are miners and nodes that reject such transactions.</p>
<p>So the question is, how is it backwards compatible and not a hard fork if nodes from before SegWit can’t spend it?</p>
<p>Thanks!</p>

CC BY-SA 4.0
2024-09-27T06:37:18.323Z
You might want to read: [What is a soft fork? What is a hard fork? What are their differences?](https://bitcoin.stackexchange.com/q/30817/121614)
Vojtěch Strnad
CC BY-SA 4.0
2024-10-07T18:02:08.333Z
This might also be interesting: https://bitcoin.stackexchange.com/q/52152/5406
Murch
<segregated-witness><blockchain-fork><soft-fork>
SegWit Soft Fork
John
# SegWit Soft Fork

(Asked by: username_0 on 2024-09-27)

my question is in relation to SegWit backwards compatibility.

Based on the way SegWit script is constructed, just 0 and a public key, makes it spendable by anyone. The only thing that stops it are miners and nodes that reject such transactions.

So the question is, how is it backwards compatible and not a hard fork if nodes from before SegWit can’t spend it?

Thanks!

**Tags:** segregated-witness, blockchain-fork, soft-fork

> **Comments:**
> **username_1**: You might want to read: [What is a soft fork? What is a hard fork? What are their differences?](https://bitcoin.stackexchange.com/q/30817/121614)  
> **username_2**: This might also be interesting: https://bitcoin.stackexchange.com/q/52152/5406  

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## 1 answers

### Answer by username_1 on 2024-09-27. Score: 3

Backwards compatibility of Bitcoin forks depends solely on whether unupgraded nodes reject blocks that are valid under the new rules. If they do, it's a hard fork, if not, it's a soft fork.

SegWit is a soft fork because SegWit outputs are spendable by anyone under pre-SegWit rules, which means there cannot be a transaction that's accepted by SegWit nodes but rejected by pre-SegWit nodes.


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