I mentioned this to someone, but Salesforce had already publicly disclosed at least 714,000 square feet in 2014 for the (now) Salesforce Tower with rumors they'd already expanded another 200k [1]. I don't think it's a particularly meaningful number either way, as what matters (if any of it does) is total square footage in the city not in a single building / lease.

[1] https://www.bizjournals.com/sanfrancisco/news/2017/05/24/sal...