The Associated Press and Al-Monitor kept US-Iran nuclear containment talks secret until after they had reached their conclusion this past weekend.
The AP claims they didn't run with the story because they couldn't get he White House or State Department to confirm the secret talks were occurring:
The AP was tipped to the first U.S.-Iranian meeting in March shortly after it occurred, but the White House and State Department disputed elements of the account and the AP could not confirm the meeting. The AP learned of further indications of secret diplomacy in the fall and pressed the White House and other officials further. As the Geneva talks between the P5+1 and Iran appeared to be reaching their conclusion, senior administration officials confirmed to the AP the details of the extensive outreach.