## Why does bitcoin-cli return strange version numbers for blocks?

3

I've been looking at the version numbers of blocks, but I'm getting strange results from bitcoin-cli getblock.

"version": 536870913


However, when I run the same command with the false option (to get the serialized block data), it shows a version number of 1:

 "result": "010000 ...


Why is this happening?

4

Great question. I had to do some research to find out.

Currently version is actually 4 bytes. In the case of this block (and many other recent blocks, as it turns out) it's 01000020. This is little endian, so when you reverse the bytes in hex it's:

0x20000001 = 536870913


Which in binary is:

00100000000000000000000000000001


It turns out that the bits here follow the BIP0009 spec. You can get a more user-friendly explanation of BIP0009 here. Essentially, BIP0009 specifies that version bits are to be used to signal support for a soft-fork. In this particular case by using that that extra "1" at the end, the miner that mined this block is expressing support for BIP0112 otherwise known as OP_CHECKSEQUENCEVERIFY.