Is there a well defined last block?

Question

It's fairly well known when the last bitcoin will be mined, but is there a well defined last block?

By that I mean, is there a block height H after which Bitcoin Core nodes will refuse to accept any further blocks due to technical limitations either within Bitcoin Core, or within the Bitcoin consensus rules as currently defined? If so, what are those limitations, what is the value of H, and how do the limitations cause the final block height to be exactly H?

This answer supposes that block production can continue to infinity, but surely there must be some technical limitation within Bitcoin Core which bounds the maximum block height, even if that block height is extremely far in the future.

Answer 1

is there a well defined last block?

I don't know of a specific limit to an exact block height like the well-defined and well-known upper limit to the money supply (<21M).

However, with the current consensus rules, the last block will be produced around Feb 7th 2106, at 06:28:15 UTC.

A hard fork sometime in the next 80 years could extend that.

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As you say there are inevitably implementation specific limits - maybe someone used an int16 for block-height somewhere. But I guess these would be relatively easy to increase in a later release of a particular software implementation.

In the network protocol, there are some limits, for example some timestamps such as the block time-stamp and lock-time are uint32. I guess it may not be possible to use lock-time after the 500 millionth block? There may be other constraints for which new messages will have to be introduced to increase the size of some fields or perhaps software changes will be needed to reinterpret them or handle them correctly.

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Answer 2

Generally, there is no defined endpoint of the blockchain. Eventually the subsidy will go to zero, but blocks would continue to collect transaction fees. In fact, since the subsidy shrinks exponentially, transaction fees may well start exceeding the subsidy in the next two decades. There are a few issues such as the space for the timestamp running out, but the time horizons for these issues are very long, and I would expect a fix for such glaring issues to be uncontroversial.

There is a well-known tongue-in-cheek counterpart to the Genesis Block, though, the Eschaton Block:

There is much talk of the Genesis block, however rarely mentioned is the Eschaton block. It is the Omega to the Genesis block's Alpha. Its hash has 256 leading zeroes, with the time required for 2^256 operations its pretext proves that the universe has [successfully] completed