Four OPEC+ sources said they only heard details of the Saudi cut at a news conference and the idea of a cut didn't come up during a weekend of discussions
Implementation of the measure, which would significantly expand eligibility now limited to the over-60s and other high-risk groups, is subject to approval by the ministry's director-general.
It was not immediately clear when that might happen.
The ministry's statement said the recommendation was made given findings that those who received a fourth shot were three-to-five times as protected against serious illness and twice as protected against infection, compared to the thrice-vaccinated.