VOCALOID-flex is a particular branch of the VOCALOID software which was designed for talking, presented in February 2010. It is more delicate to edit than the normal VOCALOID engine. It can be used in conjunction with software suits such as VTalk. It differs from the normal engine, which focus is only on singing, it however works in the same manner of assembling phonetic data. Yet despite the fact it can now be commercially bought, much of the details of the engine are largely unknown. Its development was to extend the further usage of the VOCALOID software making it feasible to use the software for private licensing.
Gachapoid and CV-4Cβ are the only two voicebanks known to use it. Further voicebanks using the software have not been confirmed. The version was also used in part with the game Metal Gear Solid: Peace Walker. It was used for several mecha known as "Gear" within the game, the most notable being "ZEKE".