The Open Philanthropy Project makes charitable grants based on what could be described as effective altruist principles: "global humanitarianism", "risk tolerance and patience", and "action in the face of humanity".
More broadly, the justification for a grant could be considered to fall under "effective altruist principles" if it is made due to a belief that it represents among the best uses of money for improving the world, without regard to favoring a particular group, nation, species, etc., and without regard to the grantmaker's personal connection to or feelings about the cause.
In the year 2031, will at least 90% of Open Philanthropy Project grants, on a dollar-weighted basis, be directed according to these principles?
The question can be judged using Open Phil's grant writups (example, which generally refer to cause reports (example), and the cause reports provide justification for why the cause is a high priority under effective altruist principles. If the outcome is disputed, a panel of three admins will vote on how it should resolve, possibly with input from the question author.
Judging this question affirmatively does not require that people agree on whether Open Phil is succeeding according EA principles, only that it is attempting to follow them. People can reasonably disagree about which causes are the most effective.
If Open Phil makes less than $1 million in grants in 2031, the question resolves as ambiguous.