The FUTURE PERFECT PROGRESSIVE TENSE indicates a continuous action that will be completed at some point in the future. This tense is formed with the modal "WILL" plus the modal "HAVE" plus "BEEN" plus the present participle of the verb (with an -ing ending): "Next Thursday, I will have been working on this project for three years."

Generally, progressive forms occur only with what are called dynamic verbs and not with stative verbs. If you wish to review that concept now, click HERE.