Conventional HPC dogma holds that native hardware FP64 silicon is the irreducible foundation of scientific computing -- the "holy grail" of double-precision simulation. This paper argues the dogma is wrong: on AI-optimised GPUs of the B300 generation and beyond, abundant FP8 tensor throughput combined with the Chinese Remainder Theorem-based Ozaki Scheme II recovers memory-roof execution at full FP64 accuracy across the canonical HPC kernel spectrum. NVIDIA's Blackwell Ultra (B300) collapses native FP64 to ~1.3 TFLOPS -- a 31x regression from the B200 -- rendering even memory-bound kernels (SpMV, GEMV, stencils) compute-bound. We make four contributions. First, a unified analytic model, the Tensor-Memory Equilibrium (TME) model, augmenting the Roofline with a compute multiplier alpha, a bandwidth multiplier beta, and a reconstruction latency gamma. Second, we identify register-level fusion as the mechanism driving beta -> 1, making emulation essentially free behind the memory wall. Third, we project that Ozaki II vaults emulated FP64 from the ~1 TFLOPS native floor to ~500 TFLOPS (B300) and ~400 TFLOPS (Rubin R200), exceeding even B200's native FP64 ceiling by over an order of magnitude in the compute-bound regime while matching the memory roof in the bandwidth-bound regime. Fourth, against an H100 baseline, Ozaki II matches or exceeds H100 on every workload studied, versus the up-to-50x regression that B300 native FP64 imposes. Combined with a companion FFT analysis (Kulisch fixed-point reconstruction on the surviving INT32 pipe) and FP32+Kahan reductions reported in the companion Part(2) paper, every surveyed kernel class on B300 reaches the memory roof at full FP64. The evidence supports the title's claim: FP8, with Ozaki II and Kulisch escape routes, is all one needs for production HPC; native FP64 silicon is no longer the holy grail it has been taken to be.

翻译：传统HPC教条认为，原生硬件FP64硅片是科学计算的不可缩减基础——双精度仿真的"圣杯"。本文论证该教条是错误的：在B300代及更先进的AI优化GPU上，通过利用基于中国剩余定理的Ozaki Scheme II，丰富的FP8张量吞吐量可恢复典型HPC核函数谱系中全FP64精度的内存天花板执行。NVIDIA的Blackwell Ultra (B300)将原生FP64性能压缩至约1.3 TFLOPS——相比B200下降31倍——导致即使是内存受限核函数（SpMV、GEMV、stencil）也变为计算受限。我们做出四项贡献：第一，提出统一分析模型——张量-内存均衡（TME）模型，在Roofline模型基础上引入计算乘数α、带宽乘数β以及重建延迟γ。第二，识别出寄存器级融合是实现β→1的机制，使得仿真计算在内存墙后几乎零成本。第三，预测Ozaki II将仿真FP64从原生FP64的约1 TFLOPS底部跃升至约500 TFLOPS（B300）和约400 TFLOPS（Rubin R200），在计算受限区域超越B200原生FP64上限一个数量级以上，同时在带宽受限区域匹配内存天花板。第四，以H100为基准，Ozaki II在所研究的每个工作负载上均达到或超越H100，而B300原生FP64则面临高达50倍的性能退化。结合配套FFT分析（在幸存INT32流水线上采用Kulisch定点重建）与配套第二部分论文中报告的FP32+Kahan缩减，B300上所有被调查的核函数类别均能在全FP64精度下达到内存天花板。证据支持本文标题的主张：通过Ozaki II和Kulisch逃逸路径，FP8即是生产级HPC的全部所需；原生FP64硅片已不再是人们所认为的圣杯。