By Ray Furlong
BBC correspondent in Berlin
They fill 381 CD-Roms, contain 290,000 agent index cards, and carry 57,000 reports of individual spying actions.
By anyone's standards, the so-called "Rosewood" files are a unique record of Cold War espionage - and now they're being laid bare to historians.
"Stasi hunters salvage the final treasure," ran one newspaper headline on Wednesday. "A new wave of Stasi investigations," reported another.
Thousands of Stasi files have already been made public
The excitement has been raised by the head of the Stasi archive, Marianne Birthler, who announced that the files had been declassified.
As archivists will wade through them over the next six months, she expects new insights into the Stasi's network in the West.
"This will help the historical reappraisal of espionage against West Germany," Mrs Birthler said.
Since the fall of the Berlin Wall, most of the archives of the Stasi - East Germany's feared secret police - have been made public.
But one part of the jigsaw was missing.
The HVA, its overseas espionage wing, managed to destroy almost all its files. Only the Rosewood files escaped the paper shredder, as they were spirited away by the CIA in as yet unexplained circumstances.
According to some reports the majority of the names in the files are East German citizens who worked for the HVA, either as instructors or couriers for operations in the West.
It is not known how the CIA came to have the files
Their names have never come to light, and no-one has excluded the possibility that some of them may still hold public office.
Light may also be shed on the little-documented HVA activity inside East Germany.
For instance, its work in promoting reforms inspired by the then Soviet leader Mikhail Gorbachev - whose policies were silently opposed by East Germany's hard-line leadership.
And for the first time, the role of thousands of Stasi collaborators in West Germany will come under scrutiny.
However, Mrs Birthler warns against expecting any sensational revelations.
Thirteen years after the collapse of communism, it is also unlikely that any criminal prosecutions will ensue.
But the opening of the archive has been welcomed nonetheless.
"It's not about sensations - the impression that the Stasi was only a problem of the former DDR citizens should now be removed for ever," noted one newspaper editorial.