17. A non-transitory computer-readable storage medium encoded with instructions that, when executed, cause at least one processor of a computing device to: output, for display, a graphical keyboard comprising a plurality of keys; maintain a plurality of letter chains, wherein: each respective letter chain of the plurality of letter chains is associated with a respective cost value; each respective letter chain includes a different respective group of one or more characters; and each respective character of each respective group of one or more characters corresponds to a respective key of the plurality of keys; receive an indication of a particular portion of a gesture detected at a presence-sensitive input device, the gesture comprising a plurality of portions; responsive to receiving the indication of the particular portion of the gesture, update, based at least in part on the indication of the particular portion of the gesture, the plurality of letter chains; determine, for the particular portion of the gesture and based at least in part on a cost value associated with at least one of the plurality of letter chains, a candidate word; and output, for display, the candidate word.
17. A non-transitory computer-readable storage medium encoded with instructions that, when executed, cause at least one processor of a computing device to: output, for display, a graphical keyboard comprising a plurality of keys; maintain a plurality of letter chains, wherein: each respective letter chain of the plurality of letter chains is associated with a respective cost value; each respective letter chain includes a different respective group of one or more characters; and each respective character of each respective group of one or more characters corresponds to a respective key of the plurality of keys; receive an indication of a particular portion of a gesture detected at a presence-sensitive input device, the gesture comprising a plurality of portions; responsive to receiving the indication of the particular portion of the gesture, update, based at least in part on the indication of the particular portion of the gesture, the plurality of letter chains; determine, for the particular portion of the gesture and based at least in part on a cost value associated with at least one of the plurality of letter chains, a candidate word; and output, for display, the candidate word. 19. The non-transitory computer-readable storage medium of claim 17 , encoded with instructions that, when executed, cause the at least one processor of the computing device to: determine a first cost value for a first key of the plurality of keys based on a first alignment point of the group of alignment points and a second cost value for a second key of the plurality of keys based on a second alignment point of the group of alignment points.