Observing time on the 10.4m GTC telescope on La Palma will form part of the in-kind contributions of the Spanish groups, IAC and BCN-MAD, to the Rubin LSST project. In this talk, we will give details on how the community can apply for this observing time, what instruments and modes will be available, and what we think are particular areas of interest. We give examples of the science interests of the IAC staff involved which can serve as inspiration for future proposals for LSST-related observing time. This presentation was delivered during the LSST@Europe6 conference in September 2024 in La Palma, Spain.