The most recent known internal history of the coup, "Zendebad, Shah!" was written by an in-house agency historian in 1998. It is heavily excised (but currently undergoing re-review by the CIA), with virtually all paragraphs marked Confidential or higher omitted from the public version. Still, it is a useful account written by someone without a stake in the events and drawing on an array of U.S. government and published sources not available to the earlier CIA authors.
This 139-page internal history prepared by the CIA's History Staff became available in highly redacted form after the National Security Archive filed a lawsuit with the CIA in 1999 for materials relating to Iran in 1953. At first it was denied in its entirety, then upon review sections already marked Unclassified were released (for the most part), along with a single section previously marked Secret (but apparently based primarily on a published account). The document is potentially of great historical value because it was prepared by a trained historian with the benefit of a variety of still-classified supporting documentation and many years of historical perspective. As such, it would be extremely useful to compare it with the only other extant internal history, which by contrast was written by one of the coup's main architects, Donald Wilber, just a few months after the operation. In its current largely inaccessible state, however, the document is mostly a testament to the continuing obstacles faced by researchers to a more complete understanding of the coup.
Source: Freedom of Information Act lawsuit