Bitcoin pool GHash.io announced on Wednesday that “it is not aiming to overcome 39.99 [percent] of the overall Bitcoin hashrate."

This marks a clear departure from the large pool’s recent flirtations with 51 percent. If that threshold is crossed for sustained periods of time, it concentrates power in ways that Bitcoin’s decentralized design normally does not allow.

“If GHash.io approaches the respective border, it will be actively asking miners to take their hardware away from GHash.io and mine on other pools,” the statement continues. “GHash.io will encourage other mining pools to write similar voluntary statements from their sides.”

Cornell professor Emin Gün Sirer, named as an attendee of this meeting, confirmed the document’s authenticity.

As Ars reported previously, once one entity achieves this simple majority, it has powers that circumvent Bitcoin’s normal decentralization. And decentralization is often held up as a salient advantage Bitcoin has over traditional currencies. These 51 percenters, for instance, have the ability to spend the same coins twice, reject competing miners' transactions, or extort higher fees from people with large holdings. Even worse, a malicious player with a majority holding could wage a denial-of-service attack against the entire Bitcoin network.

The new document is dated July 9, and it appears to be a short summary of a “round table” meeting that GHash.io and its corporate parent, CEX.io, held in London prior to the CoinSummit conference earlier this month.

Previously, CEX.io CIO Jeffrey Smith told Ars, “We never have and never will participate in any 51 [percent] attack or double spend against Bitcoin.” He did not immediately respond to Ars’ request for comment about this new 40 percent limit.

Other attendees named in the statement, including the Bitcoin Foundation, Peernova, and KnCMiner, also did not immediately respond to Ars’ request for comment.

Corporate records show that CEX.io was incorporated in London in November 2013 by two men with Ukranian names, however, the company does not state anywhere on its website who its principals are.