The delivery of military aid to Ukraine continues, but the White House cannot comment on the timing and volume of deliveries due to operational security concerns, White House Press Secretary Karine Jean-Pierre said on April 29.
that means it’s happening right meow
We know something is coming now. Some things have probably already arrived. Russia knows that too. However the what is important, if Russia knows what is arriving they can move the correct things out of range and not have them destroyed. By not saying what is arriving Ukraine can wait until something “juicy” is in range and get it by surprise. Either that or Russia will move some valuable things away from the front that the proper system to get them isn’t even coming and that means that system can’t be used against Ukraine (or it can but Ukraine has better chance to see it coming)
Russia knows all the above of course, but what can they do? (Russia likely knows more than us because of spies, but between compromised spies and not wanting to give away what a spy said may not dare do anything)