The CEFRL specifies the following:

He/she can understand a wide range of more demanding, longer texts, and recognise implicit meaning in them.
He/she can express him/herself fluently and spontaneously without much obvious searching for the right expression.
He/she can use language flexibly and effectively for social, academic and professional purposes. He/she can produce clear, well-structured, detailed text on complex subjects, showing correct use of organisational patterns, connectors and cohesive devices.