Bitcoin’s halving-eve rally broke as Coinbase access faltered

Bitcoin’s advance toward $10,000 reversed sharply on May 10, 2020 UTC, less than two days before the network was expected to reach block 630,000 and reduce its mining subsidy. The selloff interrupted a rally built partly around the approaching halving and coincided with degraded access to Coinbase’s retail and professional user interfaces.

Brave New Coin’s Bitcoin Liquid Index, a composite benchmark derived from trade and order-book data at selected liquid exchanges, recorded an hourly closing value of $8,873 at 00:00 UTC on May 10. That was $1,145, or 11.4%, below the index’s $10,018 local high on May 8. The percentage is Coinburn’s calculation from those two published index values; it is not a calendar-day return or a claim about every trading venue.

Contemporaneous reporting showed why venue and measurement definitions mattered. A Forbes report published at 01:27 UTC on May 10 said bitcoin had fallen from approximately $9,500 to as low as $8,100 on some exchanges in roughly half an hour before rebounding toward $8,700. Those figures describe selected venues and intraday extremes, whereas the Liquid Index figures are composite hourly closes. They should not be treated as interchangeable observations.

Coinbase access degraded during the move

Coinbase later established a precise operational window for the disruption. Its May 14 postmortem said the API serving coinbase.com and its mobile applications experienced elevated error rates from 17:17 to 18:00 Pacific Daylight Time on May 9—00:17 to 01:00 UTC on May 10. The error rate peaked at 00:24 UTC.

According to Coinbase, the incident affected customers’ ability to access the Coinbase and Coinbase Pro interfaces. The company said trading through its exchange APIs continued and that the underlying markets remained healthy. That distinction is important: the record supports an access failure during exceptional volatility, but it does not support a claim that Coinbase’s matching market stopped or that the outage caused the broader selloff.

Coinbase attributed the incident to increased traffic accompanying market volatility and elevated latency in outbound HTTP requests from the application instances serving its API. Timeouts then produced the customer-facing errors. That technical explanation was not available on May 10 and is included only as later operational clarification.

A crowded event met a 24-hour market

The selloff arrived amid unusually high institutional positioning. CME Group reported that open interest in its five-bitcoin Bitcoin futures contract reached a then-record 8,706 contracts, valued at approximately $407 million, on May 6. The record did not establish that futures positioning caused the May 10 reversal, but it showed that the halving was being approached through a larger regulated derivatives market than existed during Bitcoin’s 2012 and 2016 subsidy reductions.

The protocol event itself was mechanical rather than discretionary. Bitcoin Core 0.19.1 calculated the block subsidy using a 210,000-block halving interval. At block 630,000, that rule was expected to reduce the permitted subsidy from 12.5 BTC to 6.25 BTC. On May 10, however, block 630,000 had not yet been mined. Describing the subsidy reduction as completed on this date would therefore misstate the chronology.

What the reversal established

The verified record supports a narrow conclusion: Bitcoin suffered a rapid, multi-venue repricing on May 10 UTC while a major U.S. exchange operator’s customer interfaces were impaired. It does not reveal a single proven trigger. Halving-related profit-taking, leveraged positioning and thin weekend liquidity were plausible contemporaneous interpretations, but the cited records do not isolate their respective effects.

The episode mattered because it separated three risks that were often blurred together: Bitcoin’s protocol continued toward its programmed block-height event, market prices moved independently across always-open venues, and customers at one large intermediary temporarily lost reliable interface access. The halving narrative drew attention; the selloff showed that narrative alone could not remove volatility or infrastructure constraints.