Metaceramic enables ultrahigh-temperature record rectification and programmable 3D thermal control.

Thermal rectification enables asymmetric heat flow and offers transformative potential for thermal management under extreme environments, yet its practical development has been constrained by a fundamental trade-off between high-temperature stability and nonlinear thermal response. Conventional rectifiers face intrinsic limitations, with operating temperatures below 900 kelvin and rectification ratios under 3.5. Here, we present a metaceramic, a monolithic metamaterial ceramic, architected with multiscale graded porosity that synergistically integrates four nonlinear heat transfer mechanisms: ion-tailored conduction, cavity-modulated radiation, chaotic advection-enhanced convection, and spontaneous convective dissipation. This metaceramic achieves a record thermal rectification ratio of 8.5 at 2473 kelvin, surpassing previous benchmarks by over 140%. In addition, the design's continuum-like, functionally partitionable nature enables its extension into a triaxial ultrahigh-temperature rectifier, which provides programmable, volumetric thermal flow control along three independent axes, effectively elevating rectification from a scalar to a tensor-like property. By decoupling and recombining multimodal nonlinearities within a single material, we overcome the classical stability-nonlinearity conflict. Our work establishes a metamaterials platform for breaking thermal reciprocity under extreme conditions, with implications for heat management in hypersonic systems, spacecraft, and energy technologies.