caustic soda bath. double the max dose it says to use on the bottle and let it soak for about 2 hours. use a green scouring pad or four and it should come off. worked a treat on my hub when i had to strip paint. you will lose any inscribing on it and will need to polish it afterwards.
No need to spend 2 hours soaking it in caustic soda when the whole job including polishing can be done in much less time with EasyOff oven cleaner. Do not inhale this stuff and wear gloves & goggles.
I recently stripped anodize from my bars, brake lever, headset bearing cap, seatpost and seatpost clamp.
Spray stem with a good even layer then let it sit for 15mins. Wash off with water and scrub with green scourer. If any anodize still exists (most likely in tight corners etc) then repeat that process once more.
Now sand the surface with 1200 grit wet & dry (lots of water) until you are satisfied the entire surface is totally smooth and free of any anodize.
Hint: Always try to sand in the same direction of the CNC machining as it yields a better polished finish in the end result.
Now polish the stem twice with Brasso and an old cotton tee. The results are simply amazing to say the least.