High-redshift active galactic nuclei (AGN) provide key insights into early supermassive black hole growth and cosmic evolution. This study investigates the parsec-scale properties of 86 radio-loud quasars at z ≥ 3 using very long baseline interferometry (VLBI) observations. Our results show predominantly compact core and core-jet morphologies, with 35% having unresolved cores, 59% with core–jet structures, and only 6% with core–double jet morphology. Brightness temperatures are generally lower than expected for highly radiative sources. The jets’ proper motions are surprisingly slow compared to those of lower-redshift samples. We observe a high fraction of young and/or confined peak-spectrum sources, providing insights into early AGN evolution in dense environments during early cosmic epochs. The observed trends may reflect genuine evolutionary changes in AGN structure over cosmic time, or selection effects favoring more compact sources at higher redshifts. These results stress the complexity of high-redshift radio-loud AGN populations and emphasize the need for multi-wavelength, high-resolution observations to fully characterize their properties and evolution through cosmic history.

We present a comprehensive study of the faint counterjet in the radio galaxy 3C 84 using 15 years of 15 and 43 GHz data observed with the Very Long Baseline Array between 2009 and 2024. High-dynamic-range imaging reveals profound morphological and brightness asymmetry between the prominent approaching jet and the highly attenuated receding jet. The primary finding is that the counterjet provides a clean probe of subparsec external free–free absorption (FFA). The northern counterjet components N1 and N2 show strongly inverted 15–43 GHz spectra, whereas the approaching hotspot C3 is persistently optically thin, requiring a frequency-dependent absorbing screen in front of the receding flow. Taking the spectral index of α = −0.82 from C3, we infer that the FFA opacity τ _{15 GHz} changed from ∼3.0 to ∼1.9 for N1 and from ∼3.7 to ∼2.4 for N2, corresponding to emission measures of (1.7–3.3) × 10 ⁹ pc cm ⁻⁶ and electron densities of 10 ⁴ –10 ⁵ cm ⁻³ for plausible path lengths. Distinct opacity histories of N1 and N2 indicate a radially and azimuthally structured absorber, consistent with the ionized inner skin of a clumpy torus or torus-associated wind. Proper motions of C3, N1, and N2 imply a characteristic parsec-scale viewing angle of order 20° and a pattern speed of ∼0.45–0.52 c under an assumption of bilateral symmetry. Evidence for 7–11 yr transverse quasi-periodic modulation is present, but remains tentative given the limited temporal baseline and possible core-reference systematics. The counterjet of 3C 84 therefore acts as a time-dependent tomographic probe of the environment of the inner active galactic nuclei and provides a useful template for linking jet propagation to circumnuclear gas on subparsec scales.