High-fidelity gravitational waveform models are essential for realizing the scientific potential of next-generation gravitational-wave observatories. Highly accurate, state-of-the-art models often rely on extensive phenomenological calibrations to numerical relativity (NR) simulations for the late-inspiral and merger phases, which can limit physical insight and extrapolation to regions where NR data is sparse. To address this, we introduce the spinning effective-to-backwards one-body (SEBOB) formalism, a hybrid approach that combines the well-established effective-one-body (EOB) framework with the analytically driven backwards-one-body (BOB) model, which describes the merger-ringdown from first principles as a perturbation of the final remnant black hole. We present two variants building on the state-of-the-art SEOBNRv5HM model: seobnrv5_nrnqc_bob, which retains standard NR-calibrated nonquasicircular (NQC) corrections and attaches a BOB-based merger-ringdown, and a more ambitious variant, seobnrv5_bob, which uses BOB to also inform the NQC corrections, thereby reducing reliance on NR fitting and enabling higher-order (${\mathcal{C}}^2$) continuity by construction. Implemented in the open-source nrpy framework for optimized c-code generation, the SEBOB model is transparent, extensible, and computationally efficient. By comparing our waveforms to a large catalog of NR simulations, we demonstrate that SEBOB yields accuracies comparable to the highly calibrated SEOBNRv5HM model, providing a viable pathway toward more physically motivated and robust waveform models for precision gravitational-wave astronomy.

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• Gravitational wave sources
• Numerical relativity