The preparations are the clearest indication yet that Mueller is nearly done with his almost two-year investigation.
The precise timing of the announcement is subject to change.
The scope and contours of what Barr will send to Congress remain unclear. Also unclear is how long it will take Justice officials to prepare what will be submitted to lawmakers.
But with President Donald Trump soon to travel overseas for a summit with North Korean leader Kim Jong Un, Justice officials are mindful of not interfering with the White House’s diplomatic efforts, which could impact the timing.