Bitcoin Core Developer Urges Pause on BTC Transfers

Jon Atack, a Bitcoin Core developer, posted on X on June 29, 2026, advising users to avoid bitcoin transfers during the second week of August around block 961,632. He cited a risk of short chain reorganizations linked to the BIP-110 mandatory-signaling window and said he will monitor the network by running two node implementations in parallel.

BIP-110 is a temporary soft fork proposal that limits arbitrary data in transactions. New outputs would be capped at 34 bytes, OP_RETURN outputs at 83 bytes, and data pushes and witness elements at 256 bytes. UTXOs created before activation would remain exempt. The rule is designed to expire automatically after about one year.

Mandatory signaling for BIP-110 is expected to begin near block 961,632, projected for early August 2026. As of July 1–2, signaling among miners measured about 0.76%–0.79% in the current difficulty period. Bitcoin’s block height was in the mid-956,000s in early July, placing the mandatory window roughly 5,000 blocks away at that time. Nodes built from Bitcoin Knots represent an estimated 8% to 22% of the network by some metrics, while miner hashpower explicitly backing the change has been minimal.

Atack warned that the enforcement model could produce short reorganizations because BIP-110’s rules are enforced by nodes rather than by miners alone. If miner signaling lags, blocks accepted by non-enforcing nodes could be rejected by enforcing nodes, creating brief reorgs, slower block delivery for enforcing nodes, or divergence in mempool contents.

To observe network behavior, Atack plans to run a custom Bitcoin Core build and Bitcoin Knots 110 side by side to compare chain tips and rejected blocks in real time. Running two nodes with separate data directories lets an operator view both chain tips on the same machine and track rejected-block logs and mempool differences.

Responses from other developers and users varied. Developer Luke Dashjr wrote, “there is no reorg risk for users who have already upgraded to BIP-110.” Other replies ranged from calls for active testing to suggestions to ignore the advisory. Some users encouraged filling blocks with OP_RETURN data during the signaling window.

For holders seeking to reduce exposure during the window, options include moving funds out of exchanges into self-custody before mandatory signaling begins, deferring large or time-sensitive transfers until confirmations stabilize after the deadline, and asking for extra confirmations if deposits must be accepted during the period. Exchanges and wallet operators may increase required confirmation counts; if a chain split occurs, an exchange may or may not recognize transactions on one chain or the other.

If BIP-110 locks in through signaling, full enforcement of the data limits would take effect roughly 2,016 blocks after the mandatory signaling period ends, shifting full activation into mid-to-late August or early September 2026. The temporary rules would then remain in force for about a year before expiring. Atack presented his dual-node setup as an observational measure rather than a prediction of which chain, if any, would prevail.

A chain split remains a possibility but is not widely expected. By contrast, a planned August eCash fork is an intentional split that will produce two separate chains and distinct tokens. Miner signaling and network behavior over the coming weeks should clarify whether BIP-110 will lock in and how infrastructure providers respond.