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We aim to reveal the nature of the reddest known substellar companion HD206893 B by studying its near-infrared colors and spectral morphology and byinvestigating its orbital motion. We fit atmospheric models for giant planetsand brown dwarfs and perform spectral retrievals with petitRADTRANS and ATMO onthe observed GRAVITY, SPHERE, and GPI spectra of HD 206893 B. To recover itsunusual spectral features, we include additional extinction by high-altitudedust clouds made of enstatite grains in the atmospheric model fits. We alsoinfer the orbital parameters of HD 206893 B by combining the $\sim100~\mu\text{as}$ precision astrometry from GRAVITY with data from theliterature and constrain the mass and position of HD 206893 C based on the Gaiaproper motion anomaly of the system. The extremely red color and the veryshallow $1.4~\mu\text{m}$ water absorption feature of HD 206893 B can be fitwell with the adapted atmospheric models and spectral retrievals. Altogether,our analysis suggests an age of $\sim 3$-$300~\text{Myr}$ and a mass of $\sim5$-$30~\text{M}_\text{Jup}$ for HD 206893 B, which is consistent with previousestimates but extends the parameter space to younger and lower-mass objects.The GRAVITY astrometry points to an eccentric orbit ($e =0.29^{+0.06}_{-0.11}$) with a mutual inclination of $< 34.4~\text{deg}$ withrespect to the debris disk of the system. While HD 206893 B could in principlebe a planetary-mass companion, this possibility hinges on the unknown influenceof the inner companion on the mass estimate of$10^{+5}_{-4}~\text{M}_\text{Jup}$ from radial velocity and Gaia as well as arelatively small but significant Argus moving group membership probability of$\sim 61\%$. However, we find that if the mass of HD 206893 B is $<30~\text{M}_\text{Jup}$, then the inner companion HD 206893 C should have amass between $\sim 8$-$15~\text{M}_\text{Jup}$.

GRAVITY K-band spectroscopy of HD 206893 B: brown dwarf or exoplanet