9. A computing device comprising: at least one processor; and at least one module operable by the at least one processor 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.
9. A computing device comprising: at least one processor; and at least one module operable by the at least one processor 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. 10. The computing device of claim 9 , wherein the at least one module is operable by the at least one processor to: determine a group of one or more alignment points traversed by the particular portion of the gesture; determine respective cost values for each of at least two keys of the plurality of keys, wherein each of the respective cost values represents a respective probability that a respective alignment point of the group of alignment points indicates a respective key of the plurality of keys; update, based at least in part on at least one of the respective cost values for one or more of the at least two keys, the cost value associated with the at least one of the plurality of letter chains; and comparing, by the computing device, the respective combined cost values respectively associated with the plurality of letter chains to select the candidate word for outputting for display.