No you don't have to prune your pruning group 2's right now..Enjoy those blooms and after it is over blooming then you can prune to induce more vines to emerge from the soil..hopefully..you have already hard pruned your pruning group 3's as they will bloom later on in the season on the new vines they produce...Jeanne

I too would like to know about pruning. My sweet autumn clematis is a mess on my fence, but I'm uncertain what or when to do something with it.

Most experienced clematis growers recommend hard pruning ALL clematis types for at least the first couple of growing seasons regardless of pruning group. This serves to encourage the development of a strong, healthy root system able to support significant top growth, increases wilt resistance in those varieties prone to this issue and stimulates additional shooting (more stems) from the root crown. Rather than arbitrarily selecting a height, cut back to the second set of leaf nodes. These should be fairly obvious as this is where new growth buds form in pairs on either side of the stem. Often there will be remnants of last year's growth present - the old leaf petioles and maybe even last season's dried leaves. Your clematis is most likely a pruning group 2 - the vast majority of the large flowered hybrids are - and blooms on both old and new growth. Hard pruning now will eliminate the early flowers originating from the old growth but you should get a flush of blooms from the new growth a bit later in the season. If by chance it is a group 3, no worries as these all bloom on new growth and annual hard pruning is the standard practice. Typically you would want to do this a bit earlier - late winter is the timing usually recommended - but doing so now is fine and highly encouraged.

Pretty late in the season. I suggest waiting for spring. Helps to know your zone for a more specific answer. Pruning right after the first bloom allows for new growth which might give a second bloom in the fall. Here in z: 4 with our short season there isn't time for a second flush. My plants continue to put out a few blooms until frost.