Step 1: Note what the question is tracking.
It asks for the number of international organizations the United States announced it would withdraw from in 2026.
Step 2: Eliminate the smaller figures.
Numbers like 1, 18 and 25 undercount the scale of the announced withdrawals reported in the news that year.
Step 3: Recall the actual figure.
The United States announced withdrawal from as many as 66 international organizations and agreements in 2026, a sweeping diplomatic shift.
\[ \boxed{66} \]