Has Bitcoin Ever Experienced Downtime?

As a decentralized network, Bitcoin has no single points of failure, and is far less prone to outages than TradFi systems like Visa or the banking infrastructure. Nevertheless, there have been two occasions in its history where the Bitcoin blockchain has experienced downtime—albeit briefly, and without serious or lasting damage.

Overall, Bitcoin has had 99.99% uptime, and has not experienced an outage for over 10 years.

August 15, 2010: First Outage

Less that two years after Bitcoin's launch, an error in the protocol's code allowed a very large number of coins to be added to supply. Block 74,638 contained a transaction that created 184,467,440,737.09551616 BTC. Two addresses each received 92.2 billion BTC, and the miner that solved the block received an additional 0.01 BTC.

At the time, although transactions were checked before they were included in a block, there was no mechanism to avoid a case in which outputs were so large that they overflowed when summed. The problem was noticed and raised in a post on the Bitcointalk forum.

The sum of the two outputs overflows to a negative. Its a bug in the transaction checks which did not reject it, then someone noticed and exploited it. Presumably a new version will be able to reject it and start a new valid fork. meanwhile should probablt shut down whatever you can and by no means make nor accept any transactions.

Within a few hours, Satoshi had published a new version of the Bitcoin client that prevented such cases from occurring again. This resulted in a fork of the Bitcoin blockchain. The chain with 21 million BTC was accepted as the correct chain by miners, and the chain with billions of extra BTC was discarded and ceased to exist.

Overall, Bitcoin was effectively unusable for 8 hours 27 minutes. Little serious damage was done, since this was early in Bitcoin's history and there were relatively few users.

March 12, 2013: Second Outage

Bitcoin's second downtime event lasted for less time (6 hours 20 minutes) but was more significant due to the greater degree of adoption. A new copy of the Bitcoin node software was published, which turned out to be incompatible with earlier versions. A node running Bitcoin 0.8 broadcast a transaction that was not accepted by nodes running pre-0.8 software. The result was a fork, which did not automatically resolve because the two chains were supported by roughly similar amounts of hashrate.

Major miners running 0.8 downgraded back to 0.7, eventually allowing the chain to reorganize to the "old" version. One large double spend of $10,000 in BTC did take place, but not maliciously; the user was experimenting to see whether the fork had raised a security issue (documenting the process on bitcointalk), and did not defraud anyone in the process.

The fork did cause a sharp sell-off on Mt Gox, where the price briefly dropped from $48 to $37.

Other "Downtime" Events

Bitcoin hasn't had any other downtime events in the conventional sense, but there have been times when it has been unusable for other reasons.

In 2021, there was a 122-minute gap between blocks. Bitcoin is designed to average 10-minute blocks, and although there is naturally some degree of variance, it's extremely rare that it should be over two hours.

On October 13, 2011, block 149,097 took even longer to mine, 141 minutes. These delays, however, can be considered a "feature" of Bitcoin's design and a side-effect of its Difficulty adjustment mechanism, rather than a bug.

Not counting these inconveniently-long blocks, Bitcoin has not suffered any downtime in over 10 years. Anything more than a brief outage at this point would potentially be devastating for Bitcoin, which now stores half a trillion dollars of value and is used to transfer well over $10 trillion dollars every year.

This is one of the reasons that Bitcoin developers and miners are extremely conservative and resistant to any unnecessary changes in the network. Security, decentralization, and reliability are Bitcoin's most important features, and no one wants to compromise that.

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