I don’t know how solid this is, but I’ve read several posts about it lately. Also mentioned is that this results in a valuation of $8B.
Here are a few:
REPORT- Twitter Close To Finalizing Complex $800 Million Funding Deal
Twitter working on $800 million funding deal – 24by7info.in – 24-7 News
Twitter Is Said to Buy Employee Stock With Half of $800 Million in Funding – Bloomberg