<p>As with many design decisions for the original Bitcoin protocol, the answer is simply &quot;because it seemed like a good idea to Satoshi&quot;. The raw transaction format includes both variable-length numbers (called &quot;CompactSize&quot;, used for input and output counts and script sizes) and fixed-length numbers, both 4-byte (version, sequence, prevout index, locktime) and 8-byte (output amount), so in this sense the version field doesn't really stand out. Also note blocks too have a 4-byte version field.</p>

CC BY-SA 4.0
2024-10-27T10:54:53.043Z
2024-10-27T10:54:53.043Z
Vojtěch Strnad
<p>Only Satoshi Nakamoto knows the right answer :)</p>

CC BY-SA 4.0
2024-10-27T10:43:57.753Z
2024-10-27T10:43:57.753Z
amaclin
<p>Bitcoin's transaction version is 4 bytes to accommodate flexibility and make it future-proof. Indeed, this allows for diverse types of transactions as the protocol evolves. With 4 bytes or 32 bits, the number of available version numbers is over 4.29 billion in comparison with 1 byte, which has 256 possibilities, or 2 bytes, with 65,536 possibilities. Of course, this many bytes would be more than enough for future updates, as well as for something as complex as the one introduced by SegWit. Another reason for this choice is that most programming languages process data in 4-byte blocks, so this is efficient and minimizes memory alignment issues. In general, using 4 bytes keeps consistency with the protocol and fits with other fields like timestamp and block version.</p>

CC BY-SA 4.0
2024-10-30T04:35:49.610Z
2024-10-30T04:35:49.610Z
Elnora T. Marx
<p>Here is a raw bitcoin transaction. I wonder what was the reasoning to make it 4 bytes rather than 1 byte(256 possible version numbers) or 2 bytes(65536 possible version numbers)?</p>
<p><a href="https://i.sstatic.net/XIz3B7Ic.png" rel="nofollow noreferrer"><img src="https://i.sstatic.net/XIz3B7Ic.png" alt="a raw bitcoin transaction in hex format" /></a></p>

<transaction-version>
Why is the version of a bitcoin transaction is 4 bytes?
Efe
# Why is the version of a bitcoin transaction is 4 bytes?

(Asked by: username_0 on 2024-10-27)

Here is a raw bitcoin transaction. I wonder what was the reasoning to make it 4 bytes rather than 1 byte(256 possible version numbers) or 2 bytes(65536 possible version numbers)?

[![a raw bitcoin transaction in hex format](https://i.sstatic.net/XIz3B7Ic.png)](https://i.sstatic.net/XIz3B7Ic.png)

**Tags:** transaction-version


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## 3 answers

### Answer by username_1 on 2024-10-27. Score: 3

As with many design decisions for the original Bitcoin protocol, the answer is simply "because it seemed like a good idea to Satoshi". The raw transaction format includes both variable-length numbers (called "CompactSize", used for input and output counts and script sizes) and fixed-length numbers, both 4-byte (version, sequence, prevout index, locktime) and 8-byte (output amount), so in this sense the version field doesn't really stand out. Also note blocks too have a 4-byte version field.


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### Answer by username_2 on 2024-10-27. Score: 0

Only Satoshi Nakamoto knows the right answer :)


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### Answer by username_3 on 2024-10-30. Score: -2

Bitcoin's transaction version is 4 bytes to accommodate flexibility and make it future-proof. Indeed, this allows for diverse types of transactions as the protocol evolves. With 4 bytes or 32 bits, the number of available version numbers is over 4.29 billion in comparison with 1 byte, which has 256 possibilities, or 2 bytes, with 65,536 possibilities. Of course, this many bytes would be more than enough for future updates, as well as for something as complex as the one introduced by SegWit. Another reason for this choice is that most programming languages process data in 4-byte blocks, so this is efficient and minimizes memory alignment issues. In general, using 4 bytes keeps consistency with the protocol and fits with other fields like timestamp and block version.


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