tBTC halted deposits after its Bitcoin-to-Ethereum bridge hit a redemption failure

The tBTC team stopped new deposits on May 18, 2020, invoking an emergency control less than three days after its Bitcoin-to-Ethereum bridge became broadly available for mainnet ramp-up testing. The move interrupted one of decentralized finance’s most closely watched attempts to represent bitcoin on Ethereum without relying on a single institutional custodian.

Ethereum’s ledger records the successful control transaction at 05:43:14 UTC in block 10,088,196. Its logs show the tBTC system’s allow-new-deposits flag changing to false. That is the hard, independently verifiable core of the event: new deposits were disabled on-chain, not merely removed from a website.

Project lead Matt Luongo said on May 18 that deposits would be paused for 10 days and that the team was helping users withdraw. Contemporaneous reporting said the specific reason had not yet been disclosed. The responsible event-day framing was therefore narrower than the technical explanation that followed: the bridge had encountered a serious enough problem to use its one-time emergency pause, but outsiders did not yet have a complete diagnosis.

What the bridge was trying to do

tBTC was designed to issue an Ethereum ERC-20 token redeemable one-for-one for bitcoin. A depositor would send BTC to a Bitcoin wallet controlled jointly by three Keep Network signers, prove that transfer to Ethereum through a Bitcoin relay, and mint TBTC. To deter signer misconduct, the signers posted ETH bonds worth 150% of the bitcoin deposit’s value.

That architecture mattered because tokenized bitcoin was becoming a route into Ethereum lending, trading and other decentralized-finance applications. tBTC’s pitch was that distributed signers and economic collateral could reduce dependence on a central custodian. Its April 22 launch plan promised small initial lot sizes and gradual expansion, explicitly presenting the rollout as a balance between open contract access and a cautious start.

The May 18 pause tested that claim. A system marketed around minimized trust still depended on contract correctness, a relay spanning two blockchains, signer incentives and an emergency mechanism controlled through a technical wallet. The stop did not by itself prove lost user funds or a broken bitcoin backing ratio. It did demonstrate that cross-chain risk extended beyond custody: an error in how one chain interpreted evidence from another could threaten the bridge’s economic safeguards.

Scope and market limitations

The available record does not support a claim that the incident moved the broader BTC or ETH markets. No reliable event-window study tied spot prices, volumes or liquidations to the pause, and the alpha interface limited ordinary deposits to 0.001 BTC. The central significance on May 18 was institutional and technical, not a measured market-price shock.

Likewise, the team’s statement that it was assisting withdrawals was a contemporaneous project claim, not an independently completed accounting on May 18. The on-chain pause proves that new deposits were turned off; it does not alone establish the status of every existing deposit, signer bond or unit of TBTC.

Later incident record

In a May 20 postmortem, Keep Network said a redemption attempt using certain Bitcoin address types exposed faulty output-script validation. The team said the flaw could prevent Ethereum contracts from accepting proof that a Bitcoin redemption had completed, putting signer bonds at risk of liquidation. It reported that all three active signers were controlled by one operator, that the hosted alpha interface used a 0.001 BTC lot size, and that a proposed code fix and additional testing were underway.

Those details clarify the May 18 action but were not all available when the pause first became public. The durable lesson from the event date is narrower: a live, trust-minimized bridge encountered a redemption-path failure, and its emergency brake worked before the project had finished explaining the fault.