Subject: [bitcoindev] OP_CHECKUTXOSETHASH idea

From: Erik Aronesty <[email-masked]>
Date: Mon, 29 Sep 2025 17:09:15 -0700

A soft fork could introduce a new opcode, `OP_CHECKUTXOSETHASH`, allowing
miners to optionally commit a deterministic hash of the current UTXO set
into a block. If present, all nodes must verify its correctness or reject
the block; if absent, the block is still valid. Old nodes treat the opcode
as unspendable, so backward compatibility is preserved.

Because computing the full UTXO root is costly, this makes each checkpoint
intentionally expensive to produce, ensuring that miners will only include
them when compensated with sufficient fees. Additionally, it could be
limited to one per block.

The result is a voluntary, self-limiting, incentive-aligned, fee-driven
system where checkpoints are cheaply consensus-enforced when included but
never mandatory.

Most nodes could operate on a rolling history validated by occasional,
high-value commitments, while archival nodes remain free to preserve the
full chain. This reduces the burden of initial sync and resource use
without sacrificing Bitcoin’s security model, since any invalid checkpoint
would invalidate its block.

In practice, the chain becomes more efficient for everyday use while the
historical record remains intact for those willing to bear the expense of
maintaining it.

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