summitpost.org:
Being the most direct access to Baxter Peak, the Abol Trail has the reputation to be steep and relentless. The Abol Trail was closed from spring 2014 to summer 2016 due to a rock slide that occurred in 2013. A new trail segment has been opened, which, before reaching the rock slide, will diverge to the northwest, making a traversing ascent before switchbacking along the rib that is west of the slide. The route is now slightly longer (3.6 instead of 3.2 miles), less steep (average 30% instead of 47% on the slide part), and slightly easier (less scrambling and firmer ground). However, the most challenging part, the upper slide, remains unchanged. The GPS track on this page includes both the new and the old trail.
As a result of the re-route, new FKTs will have to be set for the new trail. There is a Strava segment for the ascent.
Another route is the Helon Taylor Trail from the Roaring Brook CG over Pamola Peak. It is about 4.1 miles each way.
Still another way is the Hunt Trail from the Katahdin Stream parking lot, about 4.6 miles each way.
The Thoreau Traverse ascends the Hunt Trail from Katahdin Stream to the top & then down to Roaring Brook via the Helon Taylor Trail (or the other direction). It is logical to do this out & back, unless one has arranged a shuttle of some sort.
The Katahdin Cirque variation follows the rim of the South and Great Basins. It is as pure an alpine running route as it gets in New England with treeline dropping out at around 3,500 feet and a long stretch of exposed, highly technical terrain. The route starts at the Roaring Brook Campground heading up the Chimney Pond Trail for a brief moment and then quickly diverges onto the Helon Taylor Trail. This is followed to Pamola Peak and then in and out of "the chimney" and off onto the Knife Edge, a thin, one mile pile of rocks leading to Katahdin's South Peak and eventually the summit proper. From there you run along the edge of the Table Lands, past the Cathedral and Saddle Trails and north along the Northwest Basin Trail. Upon reaching the Hamlin Ridge Trail you head east to the Hamlin Peak summit and descend back into the cirque. At the bottom of the ridge take a right to the North Basin Trail eventually intersecting back with the Chimney Pond Trail, which will take you back to Roaring Brook. This loop is the most obvious on the east side of the mountain and provides high adventure in a remote part of New England. The Katahdin Cirque Route clocks in at about 10.7 miles with an elevation gain of 4,800 feet. Parking is very limited at the Roaring Brook Campground and you must make sure you have a day use pass or have reserved a campsite. Additionally you must sign in and out of the trail register at the Roaring Brook ranger station. The only (mostly) reliable water source on the mountain is at Caribou Springs, just before heading up to Hamlin Peak.
