It's unclear whether that number included the arena, which cost about $1 billion, including infrastructure. But it's safe to say it's all a moving target, especially since costs surely will escalate during the buildout, which will last until (at least) 2025.
Now comes an 8/18/16 press release from Greenland USA about the company's third U.S. investment, Greenland USA Acquires 42-Acre Property in South San Francisco's Oyster Point, which includes the following paragraph:
The Landing at Oyster Point follows Greenland USA's $1B+ investment in Los Angeles' Metropolis and $6B+ investment in New York's Pacific Park Brooklyn. Both projects exemplify Greenland USA's expertise and vision for developing transformative properties in gateway cities that also support the local economy and foster the growth of the surrounding communities.This syntax implies that Greenland would invest $6 billion-plus, which, if taken literally, means Forest City Enterprises would contribute another $2.5 billion-plus. Highly unlikely. And, of course, neither wants to use their own money, and are trying to sell three building sites.
But it's likely safe to say the entire project's price tag will ultimately exceed $6 billion--easily, if the arena's included, and likely, even without.