<p>Bitcoin clients no longer use version 2 or version 1 in the block headers. Block version is now defined as per <a href="https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki" rel="nofollow noreferrer">BIP-9</a>, and miners use specific bits in the block version number to signal their support for specific soft-forks in the bitcoin protocol. The top 3 bits of the blocks must be 001, so the range of actually possible nVersion values is from 0x20000000 to 0x3FFFFFFF, both inclusive.</p>

CC BY-SA 4.0
2019-03-24T15:00:17.797Z
What! why must the first 3 bits be 001? Thanks for the reply. And also, yea, I am looking at the Bitcoin-ABC code, and there does seem to be a lot of different numbers inside of it.
nick carraway
CC BY-SA 4.0
2019-03-24T15:09:50.030Z
According to BIP-9, "When a block nVersion does not have top bits 001, it is treated as if all bits are 0 for the purposes of deployments." Thus, if the top 3 bits are not set as 001, miner will not be able to indicate his support for active proposals.
Ugam Kamat
CC BY-SA 4.0
2019-03-24T15:18:30.173Z
Thanks, of  course I read BIP 9 and I realized the reasons for it
nick carraway
CC BY-SA 4.0
2019-03-24T10:23:48.857Z
2022-10-17T19:28:53.117Z
2022-10-17T19:28:53.117Z
Ugam Kamat
<p>Is Bitcoin Core the only protocol that uses these version numbers? </p>

<p>Does anyone know what ABC and Unlimited use?</p>

<p>Is there a place where I can see the raw version numbers for each client easily?</p>

<mining-pools><mining-hardware>
What clients use version number "2" and version number "1" in their block headers?
nick carraway
# What clients use version number "2" and version number "1" in their block headers?

(Asked by: username_0 on 2019-03-24)

Is Bitcoin Core the only protocol that uses these version numbers?

Does anyone know what ABC and Unlimited use?

Is there a place where I can see the raw version numbers for each client easily?

**Tags:** mining-pools, mining-hardware


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## 1 answers

### Answer by username_1 on 2019-03-24. Score: 2 | Accepted answer

Bitcoin clients no longer use version 2 or version 1 in the block headers. Block version is now defined as per [BIP-9](https://github.com/bitcoin/bips/blob/master/bip-0009.mediawiki), and miners use specific bits in the block version number to signal their support for specific soft-forks in the bitcoin protocol. The top 3 bits of the blocks must be 001, so the range of actually possible nVersion values is from 0x20000000 to 0x3FFFFFFF, both inclusive.

> **Comments:**
> **username_0**: What! why must the first 3 bits be 001? Thanks for the reply. And also, yea, I am looking at the Bitcoin-ABC code, and there does seem to be a lot of different numbers inside of it.  
> **username_1**: According to BIP-9, "When a block nVersion does not have top bits 001, it is treated as if all bits are 0 for the purposes of deployments." Thus, if the top 3 bits are not set as 001, miner will not be able to indicate his support for active proposals.  
> **username_0**: Thanks, of  course I read BIP 9 and I realized the reasons for it  

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