“I propose to consider the question, ‘Can machines think?’”
– Alan Turing, *Computing Machinery and Intelligence* (1950)

In a post to arXiv, now under peer review, two researchers at UC San Diego report the first experimental demonstration of LLMs passing the Turing test. Originally called the Imitation Game the Turing test has had a profound influence on the field of AI for 75 years. The test has been the subject of both volumes of academic analysis and popular fiction. A machine’s passing the test has been called an epochal moment for man.
Turing’s Imitation Game
As there have been many interpretations of the test, it might be worth noting why the UCSD version is important and closest to Turing’s original proposal. Turing described a so-called 3-party test in which a judge (human) interacts with a man and a women via text, and must decide which is which. Then, one of the participants is replaced with a machine which is tasked with fooling the judge into thinking it is human.
The UCSD version is also a 3-party test in which a human interrogator simultaneously interacts with a human and an LLM, both of which must convince the interrogator that they are human. The LLM passes the test if on average the interrogator cannot identify the human. In UCSD’s study, a baseline was set with the classical ELIZA chatbot, while LLM models included OpenAI’s GPT-4o an GPT-4.5 and LLaMa-3.1-405B from Meta.
There are a number of subtleties that make test implementation complex, but one in particular is of interest for this post. The behavior of an LLM is a function of both its pretraining and the context at query time. This context, if persistent across queries, is often defined in the system prompt and can be instructions for how the LLM should act. Sentienta calls this context the persona, as do the UCSD researchers. In their study, only LLMs with an adequately defined persona were able to pass the test. The winning persona had been fine-tuned by playing against human judges on the website turingtest.live. When paired with this persona, GPT-4.5 was chosen as the human participant 73% of the time, convincingly passing the test.
What Does Passing the Turing Test Mean?
Turing was interested in the question “Can machines think?” and came up with the imitation game in order to operationalize it. Does passing the test mean that an LLM can think? That depends on what we mean by “thinking”. This study demonstrates that LLMs can use language and reasoning well enough to convincingly imitate human intelligence, and fool human interrogators. What it does not do is demonstrate either machine consciousness or even understanding.
Nonetheless, the three-party Turing test sets a high bar. As the authors note, to win this version of the test, the LLM must not only appear human—it must appear more human than the other participant. This is a difficult task: interrogators correctly observed that the human participant lacked knowledge an AI might possess or made errors an AI wouldn’t make. In other words, for the LLM to win, it must display not only intelligence, but also human fallibility.
Reference:
Christian, Brian. The Most Human Human: What Artificial Intelligence Teaches Us About Being Alive . New York: Anchor Books, 2012.
Turing, Alan M. Computing Machinery and Intelligence . Mind, Vol. 59, No. 236, 1950, pp. 433–460.








