Final Taproot Activation Specifics Chosen With a Bitcoin Blockchain 'Coin Toss'

The coin toss is a stand-in for the rough consensus that stakeholders usually broker to make these decisions.

Apr 7, 2021 at 2:35 a.m. UTC
Updated Sep 14, 2021 at 12:37 p.m. UTC

Bitcoin developers couldn’t settle on the specifics of Taproot’s activation, so they used a “coin toss” on the Bitcoin blockchain this Tuesday to wrap up activation discussions that began a year ago.

According to blockchain data pulled from this journalist's Bitcoin node, the result of the coin toss has determined that Taproot’s activation timeline will be measured using median time passed (MTP) instead of block height.

For the actual "toss," the last digit of the block 678079's hash were used to decide the outcome where a value of 0 represented MTP and a value of 1 represented height. 

Screenshot of coin flip result

Taproot – an upgrade that will enrich Bitcoin’s smart contracts – is all set to go using the “Speedy Trial” activation method outlined a month ago. Today’s coin toss settled a dispute, though, over how the Bitcoin blockchain will measure the time that has passed between when the upgrade is released and when it will “time-out.” 

Block height vs. MTP

There were two options up for debate: one using “block height,” which chooses a timeout that triggers once a specific block is mined and the other using MTP, which chooses the timeout based on real-world time derived from block data.

The coin toss occurred on block 678079 and the result landed on MTP. Following the result, Bitcoin Core contributor Andrew Chow removed his pull request for a block height-based scheme.

MTP means that when Taproot’s code is shipped, miners and node operators will have a time period of exactly three months to upgrade to Taproot before a timeout period is reached. 

If miners representing 90% of Bitcoin’s hashrate upgrade in this timeframe, then Taproot is “locked in” and it will activate three months after this lock-in. Assuming Taproot is shipped by May, this means the upgrade would be fully functional on the Bitcoin blockchain no later than November.

“We have two good options, and coin flip is people agreeing to put aside minute preferences on two acceptable options for the big picture," Bitcoin Core contributor Jeremy Rubin wrote in a Bitcoin devlist email. “As such, I think that a coin flip is appropriately used in this circumstance, although I recognize the sentiment that some may feel it's treating development a little too *flippantly*.”

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