The development team at Valve utilize what is known as a User Picker tool, a device which allows users to track projects and the individuals working on them.
This tool is not supposed to be seen by the public, but by mistake the company made the Picker tool accessible to the public where many were able to view the staff currently working on Half-Life 3 and Half-Life 3 Core which may be used in conjunction with the main title. 

There are currently 46 people working on the main title at Valve and another 10 people are busying away at the Core project, according to Gematsu.

Many are now starting to speculate if Valve released this information in order to announce Half-Life 3 without doing it through regular media streams. There is a sense of disbelief that Valve would allow this information to escape by mistake.

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