Level C1 corresponds to users who can express themselves fluently and spontaneously. They can use language flexibly and effectively for all purposes.
It is important to bear in mind that the Common European Framework of Reference for Languages (CEFR) is the system that defines and explains the different levels of oral and written expression and comprehension for languages such as English. It consists of 6 levels of reference: three blocks (A or basic user, B or independent user and C or proficient user), which are in turn divided into two sublevels, 1 and 2.
SKILLS AT LEVEL C1
One of the questions you might ask yourself when you read this information is, what language competences characterise a person who can prove they have a level C1 in English? The CEFR 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.