The extended bronze plan is an addition to the bronze metal level. The plan will have an average actuarial value (AV) of 60 percent, but that number is allowed to range from 56 percent to 65 percent. The expansion that allows the coverage percentage to go beyond the average minimum and maximum percentages (-4% or +2% AV) gives this plan its name.

References

https://www.qhpcertification.cms.gov/s/Plans%20and%20Benefits | http://healthaffairs.org/blog/2016/12/18/the-final-2018-notice-of-benefit-and-payment-parameters-part-2/