We present the discovery of a pair of transiting giant planets using four sectors of TESS photometry .
TOI-216 is a 0.87 M _ { \odot } dwarf orbited by two transiters with radii of 8.2 R _ { \oplus } and 11.3 R _ { \oplus } , and periods of 17.01 d and 34.57 d , respectively .
Anti-correlated TTVs are clearly evident indicating that the transiters orbit the same star and interact via a near 2:1 mean motion resonance .
By fitting the TTVs with a dynamical model , we infer masses of 30 _ { -14 } ^ { +20 } M _ { \oplus } and 200 _ { -100 } ^ { +170 } M _ { \oplus } , establishing that the objects are planetary in nature and have likely sub-Kronian and Kronian densities .
TOI-216 lies close to the southern ecliptic pole and thus will be observed by TESS throughout the first year , providing an opportunity for continuous dynamical monitoring and considerable refinement of the dynamical masses presented here .
TOI-216 closely resembles Kepler-9 in architecture , and we hypothesize that in such systems these Saturn-analogs failed to fully open a gap and thus migrated far deeper into the system before becoming trapped into resonance , which would imply that future detections of new analogs may also have sub-Jupiter masses .