I activated this summit a few years ago, so doing this write up based on the best of memory.
Back then you did not need a permit for day hiking or staying overnight in the Three Sisters Wilderness. Today you will need to apply for an overnight permit if you are camping, as well as a day hike permit for certain trail heads. See the following link https://www.recreation.gov/permits/4675311 for info on how to obtain a Central Cascades Wilderness permit, as well as this map
showing the current trail heads that require a permit and trail heads that have free self issue permits at the trail head.
I started my hike at the Devils Lake/South Sister trail head, though other trail heads would suffice, such as Sisters Mirror or Elk Lake. I hiked to Sisters Mirror Lake, and from there got onto trail 2000. From there it is a small climb/walk off trail (a few feet if I recall) to a small spot in the forest within the activation zone.
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