On December 21, 2024, just before 2 p.m., scientists made the dead speak. ELIZA, the world’s first chatbot it’s back. Long imitated, but not completely imitated, ELIZA was long thought lost. But scientists discovered an early version of its code in its maker’s archives in 2021 and spent the intervening years piecing it together.

ELIZA has been reanimated and you can download it here to see for yourself.

Coded and iterated from 1964 to 1967, ELIZA was developed by MIT computer scientist Joseph Weizenbaum. Standard by today’s standards, ELIZA was a hit during its production. He gave it the personality of a psychotherapist and his secretary was so taken with it, that she asked Weizenbaum to leave the room when he chatted with her.

A new scientific paper from members of the ELIZA Archeology Project detail how they found and resurrected the chatbot as well as its origins and subsequent dissemination. Weizenbaum programmed ELIZA in an early language called MAD-SLIP on a time-sharing computer system called the Compatible Time-Sharing System or CTSS.

ELIZA quickly got away from Weizenbaum. As it spread through the early computer networks, programmers adapted it to other languages. One of the early clones was built in Lisp by one of the technical leaders of ARPAnet, the forerunner of the modern internet. The Lisp version of Eliza was one of the first bits of data on this new network and it spread rapidly.

“As a result, Cosell’s Lisp ELIZA quickly became the dominant strain, and Weizenbaum’s MAD-SLIP version, invisible on ARPAnet, was consigned to history,” the paper said. “Until it is rediscovered in 2021, the original MAD-SLIP ELIZA has not been seen by anyone for at least 50 years.”

A decade ago, a magazine called Creative Computing published an ELIZA clone written in BASIC. That was 1977, the same year that the Apple II, Commodore Pet, and TRS-80 all hit the market. Those machines led to an explosion in home computing and the proliferation of the BASIC computing language.

“And probably not a small number of hobbyists are interested enough in the possibility of AI to type in this BASIC ELIZA (which is only a couple of pages of code), and experiment with it themselves,” said of scientists. “Because of its brevity and simplicity, and the explosion of the personal computer, this ELIZA spawned hundreds of knock-offs over the decades, in every imaginable programming language, making it perhaps the most failed program in history / Just as Cosell’s Lisp ELIZA spread through the ARPANet, BASIC ELIZA spread through the explosive spread of personal computers.

There are countless versions of this BASIC version of ELIZA online today and the original MAD-SLIP version was long thought lost to history. Then Stanford computer scientist Jeff Shrager convinced MIT archivists to root through boxes of Weizenbaum material and they made a critical discovery: early versions of the MAD-SLIP code.

The code is incomplete, and it requires a lot of tinkering and complex simulation to get it running again. “This requires many steps to clean up and complete the code, install and debug the emulator stack, non-trivial debugging of the found code itself, and even write some new function not found in the archives or in the available MAD and SLIP implementations,” the paper says.

It took time and a lot of effort, but code archaeologists reworked ELIZA and made it available for anyone to play with. “It’s been tested on different versions of Linux and MacOS, but we’ve noticed some issues with different versions, so your mileage may vary,” they said in the paper. “If you run it on your machine and realize you need to change something, let us know.”