It is a word. Performant means "performing well". I wonder if can we apply this kind of adjective-forming to other verbs, e.g. by taking the gerund form, removing "-ing" and adding the suffix "-ant".

For example:

- observing => observant =?= observing well (yes, exists in this meaning)

- informing => informant =?= informing well (does not exist as adjective, but could in the future?)

- thinking => thinkant =?= thinking well (does not exist at all, but could in the future?)