The unreported letter and AI algorithm was a critical development ahead of the board's ouster of Altman and was apparently on the list of grievances by the board that led to Altman's firing.

So far the letter has not been made public but it is believed to be about a project called Q which was sent to the Board before the drama kicked off.

ChatGPT had made progress on Q* (pronounced Q-Star), which some internally believe could be a breakthrough in the startup's search for superintelligence, also known as artificial general intelligence (AGI).

OpenAI defines AGI as AI systems that are smarter than humans. Given vast computing resources, the new model solved some mathematical issues. Though only performing math on the level of grade-school students, acing such tests made researchers optimistic about Q*'s future success, the source said.

However, maths is at the frontier of generative AI development. Currently, generative AI can write and translation language by statistically predicting the next word which it is not that reliable at doing. However, in maths, there can be only one right answer and it means that AI could be applied to scientific research.

 Unlike a calculator that can solve a limited number of operations, AGI can generalise, learn and comprehend. In their letter to the board, researchers flagged AI's prowess and potential danger, the sources said, without specifying the exact safety concerns noted in the letter.