We propose Sci-Fii, a speculative conversational interface framework for incremental inference on modularized services. To build one's own conversational interface with existing business logic, cloud-based modularized services offer a suite of ready-to-use components to ease development, ensure cross-platform flexibility, and encapsulate computational complexities. However developing with the modularized services often results in a chain of discrete modules with limited inter-module data sharing, which yields unnecessarily long response times of the conversational interface, aggravates user experiences, and eventually harms user retention. Sci-Fii offers a uniform framework that enables existing serviced modules to benefit from intermediate data and early parallel execution. Transparent to developers, Sci-Fii helps the end-to-end conversational interface system work fluidly and exhibit faster and more natural response times.