(Minor spoilers for Too Like the Lightning. Names may be spelled wrong because I am listening to the audiobook, not reading.)
Too Like the Lightning pre-reveals the identity of its Anonymous far before it officially reveals it. I don't think this is even supposed to be foreshadowing, because while it's subtextual, it's not subtle. At one point, Mycroft notes that Anonymous had published something relevant to the crisis and that while Vivien, the Consul, couldn't do anything himself, he had "found a way" to act. And in chapter 30, when Anonymous is waiting impatiently for Bryar Kosala, that confirms it even more strongly. So when it's 'properly revealed' later in the same chapter, it's not a surprise — it serves mainly to clarify: "Yep, the thing that was heavily heavily implied is true, you don't have to think about it more."
This is interesting because it's not a twist that he turns out to be Anonymous. It's not a secret. It just didn't happen to be relevant enough to make so nearly explicit until chapter 30.