They had the sophons which allowed them to convey information via quantum entanglement, i.e. instantly. They - and the humans - developed close to light speed

They had the sophons which allowed them to convey information via quantum entanglement, i.e. instantly. They - and the humans - developed close to light speed traveling which IIRC has the same underlying mechanics as that blackout-galaxy-safe-space thing which is the message that your civilization is not harmful.