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tokens: manuscript, we report on the results of the monitoring of MAXI J1631-472 with the MeerKAT interferometer, complemented with X-ray data from Swift and MAXI . We show the evolution of the radio and X-ray emission throughout its outburst and provide a physical interpretation of the data set. We also compare the behaviour observed with other known outbursting BH systems. The paper is structured as follows: in Section 2 , we describe the observations and details of the data reduction. In Section 3 , we present the results of the two wavebands and highlight some of the interesting behaviour. In Section 4 , we summarize our conclusions. 2 OBSERVATIONS 2.1 MeerKAT The MeerKAT monitoring of MAXI J1631-472 was performed weekly, with the observations carried out at a central frequency of 1.28 GHz and bandwidth of 856 MHz. These observations were taken as part of the ThunderKAT Large Survey Programme on MeerKAT (Fender et al. 2016 ). Each observation consists of a 15-min scan of the target, and a 2-min scan of the phase calibrator, in this case J1726-5529. The primary calibrator used was J1939-6342, which was observed at the start of each observation for 5 min. We used casa (McMullin et al. 2007 ) to perform the data reduction. We performed flagging of radio frequency interference, where we removed the first and last 150 channels (channel width ∼ 209 kHz) of the band. The autoflagging algorithms, rflag and tfcrop , were used for subsequent flagging. We then performed calibration, where the flux density on the primary calibrator was set using the known model. The phase-only and antenna-based delay corrections on the primary calibrator were then solved for, then the bandpass corrections for the primary were then applied. We solved for the complex gains on the primary and secondary, then proceeded to scale the gain corrections from the primary to the secondary and target source. Finally, the imaging was performed using wsclean (Offringa et al. 2014 ). Flux densities for MAXI J1631-472 were extracted from the images using pybdsf (Mohan Rafferty 2015 ); these are presented in Table 1 . We were able to extract an in-band spectral index (α, with the flux density S ν scaling with frequency ν as S ν ∝ ν α ) at the four brightest epochs using a fit to eight uniformly spaced channels across the 856 MHz bandpass. To determine the spectral index, we performed a least-squares fit using the scipy and curve-fit module and function, respectively, in python to calculate the slope and its associated error bar. The results from these fits are presented in Table 2 and indicate that the source was optically thin during the times of strongest radio flux density. Table 1. MeerKAT radio (1.28 GHz) and Swift X-ray (1–10 keV) fluxes of MAXI J1631-472. The spectral states of each of the observations are indicated in the final column: Soft (S), intermediate (I) and Hard (H). Table 2. Spectral indices during the strongest radio flux: S ν ∝ ν α . 2.2 MAXI We used X-ray data from the