Efficient anion recognition is of great significance for radioactive ⁹⁹TcO₄⁻ decontamination, but it remains a challenge for traditional sorbents. Herein, we put forward a tactic using soft crystalline cationic material with anion-adaptive dynamics for ⁹⁹TcO₄⁻ sequestration. A cucurbit[8]uril-based supramolecular metal-organic material is produced through a multi-component assembly strategy and used as a sorbent for effective trapping of TcO₄⁻. Excellent separation of TcO₄⁻/ReO₄⁻ is demonstrated by fast removal kinetics, good sorption capacity and high distribution coefficient. Remarkably, the most superior selectivity among metal-organic materials reported so far, together with good hydrolytic stability, indicates potential for efficient TcO₄⁻ removal. The structure incorporating ReO₄⁻ reveals that the supramolecular framework undergoes adaptive reconstruction facilitating the effective accommodation of TcO₄⁻/ReO₄⁻. The results highlight opportunities for development of soft anion-adaptive sorbents for highly selective anion decontamination.