In situ high-temperature nuclear magnetic resonance (NMR) spectroscopy can be very useful for probing changes in structure and dynamics in glass-forming liquids, and is a unique method for observing chemical exchange among structural species (e.g. BO 3 –BO 4 , Q n –Q n+1 , and NBO–BO) at the seconds to microseconds time scales. High-temperature 11 B MAS NMR line shape measurements were made at about 100K above the glass transitions on (Na 2 O) 0.3 (B 2 O 3 ) 0.7 and (Na 2 O) 0.2 (B 2 O 3 ) 0.21 (Al 2 O 3 ) 0.08 (SiO 2 ) 0.51 glass-forming liquids. BO 3 and BO 4 groups are well resolved in 11 B MAS NMR spectra at 14.1T with sample spinning at 5000Hz. At higher temperatures, partial peak coalescence occurred due to exchange of BO 3 and BO 4 . Temperature effects on borate speciation were also determined by varying the fictive temperature (T f ) of glasses, where T f estimated from differential scanning calorimetry measurements. We combined these complementary data sets to model structural exchange in the liquid state. The time scale of BO 3 –BO 4 exchange from NMR data, τ NMR , appears to be “decoupled” from that of the macroscopic shear relaxation process τ s derived from the viscosity, however, at higher temperatures, τ s approaches τ NMR . The “decoupling” at lower temperature may be related to intermediate-range compositional heterogeneities, and/or fast modifier cation diffusivities which trigger “unsuccessful” network exchange events.