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?

1 Answer 1


Bitcoin clients no longer use version 2 or version 1 in the block headers. Block version is now defined as per BIP-9, 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.

  • 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. Mar 24, 2019 at 15:00
  • 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.
    – Ugam Kamat
    Mar 24, 2019 at 15:09
  • Thanks, of course I read BIP 9 and I realized the reasons for it Mar 24, 2019 at 15:18

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