AMD Instinct MI455X vs NVIDIA B300 SXM6 AC Comparison

Where Each One Wins

The recorded data draws a clear line between the two accelerators. The AMD Instinct MI455X wins outright on raw compute scale and memory capacity, while the NVIDIA B300 SXM6 AC wins on measured performance, efficiency, and production readiness. There are no shared benchmark results in the database, so the comparison rests on architectural specifications and the single recorded OpenCL score for the NVIDIA part.

The AMD Instinct MI455X delivers 157.3 TFLOPS FP32 and 157.3 TFLOPS FP16 (1:1), which is more than double the NVIDIA B300 SXM6 AC's 76.99 TFLOPS in both precisions. The AMD part also holds 432 GB of HBM4 memory versus 288 GB of HBM3e, and its 23.3 TB/s memory bandwidth is nearly three times the NVIDIA part's 8.19 TB/s. These figures position the MI455X as the compute-density leader on paper.

The NVIDIA B300 SXM6 AC counters with an actual benchmark result: a Geekbench OpenCL score of 369,831, which places it in the 100th percentile of all GPUs in the database. Its nearest rivals trail by 7% (NVIDIA B200), 10.4% (NVIDIA H200 NVL), 16.3% (AMD Instinct MI300X), and 25% (NVIDIA L40S). The AMD MI455X has no recorded benchmark score and sits at the 50th percentile, with an average benchmark score of zero in the database.

The NVIDIA part is also the only one with an active production status. The AMD part lacks a production status entry, which means the database cannot confirm it as a shipping product. The NVIDIA part has a clear release date of September 2025, while the AMD part's release date is July 2026. The NVIDIA part lists a successor (Server Rubin), while the AMD part does not.

Architecture Differences

The two accelerators come from different design philosophies. The AMD Instinct MI455X uses the CDNA 5.0 architecture on a 2 nm TSMC process, packing 320,000 million transistors into a 2990 mm² die. The transistor density works out to 107.0M per mm². The NVIDIA B300 SXM6 AC uses the Blackwell Ultra architecture on a 5 nm TSMC process, with 208,000 million transistors on a 1628 mm² die, giving a higher density of 127.8M per mm².

The chip-level differences are substantial. The AMD part uses the MI450 256CU chip, while the NVIDIA part uses GB110. The AMD part has 32,768 shading units, 1,024 TMUs, and zero ROPs. The NVIDIA part has 18,944 shading units, 592 TMUs, and 24 ROPs. The NVIDIA part includes 592 tensor cores, while the AMD part lists no tensor core count. Neither part lists ray tracing cores.

Memory architecture diverges completely. The AMD part uses HBM4 with a 24,576-bit bus and 432 GB capacity, reaching 23.3 TB/s. The NVIDIA part uses HBM3e with an 8,192-bit bus and 288 GB capacity, reaching 8.19 TB/s. The AMD part's memory clock is 1900 MHz (7.6 Gbps effective), while the NVIDIA part runs at 2000 MHz (8 Gbps effective).

Clock behavior also differs. The AMD part has a 1000 MHz base clock and 2400 MHz boost. The NVIDIA part has a 1665 MHz base clock and 2032 MHz boost. The NVIDIA part starts higher but boosts lower, while the AMD part has a wider clock range.

Power figures separate the two sharply. The AMD part draws 2300 W TDP with a 2700 W suggested PSU. The NVIDIA part draws 1100 W TDP with a 1500 W suggested PSU. The AMD part uses an EAM Module slot width, while the NVIDIA part uses an SXM Module. Both connect via PCIe 6.0 x16, and neither has display outputs or API support for DirectX, OpenGL, or Vulkan.

FAQ

Q: Which accelerator has higher FP32 compute?

A: The AMD Instinct MI455X delivers 157.3 TFLOPS FP32, which is more than double the NVIDIA B300 SXM6 AC's 76.99 TFLOPS FP32.

Q: How much memory does each accelerator provide?

A: The AMD Instinct MI455X provides 432 GB of HBM4 with 23.3 TB/s bandwidth. The NVIDIA B300 SXM6 AC provides 288 GB of HBM3e with 8.19 TB/s bandwidth.

Q: Which part has a recorded benchmark score?

A: Only the NVIDIA B300 SXM6 AC has a benchmark entry: a Geekbench OpenCL score of 369,831, placing it in the 100th percentile. The AMD Instinct MI455X has no recorded benchmark scores and sits at the 50th percentile.

Q: What is the transistor count difference?

A: The AMD Instinct MI455X contains 320,000 million transistors on a 2990 mm² die. The NVIDIA B300 SXM6 AC contains 208,000 million transistors on a 1628 mm² die. The NVIDIA part has the higher transistor density at 127.8M per mm² versus 107.0M per mm².

Q: Which accelerator has a higher boost clock?

A: The AMD Instinct MI455X boosts to 2400 MHz, while the NVIDIA B300 SXM6 AC boosts to 2032 MHz. The NVIDIA part has the higher base clock at 1665 MHz versus 1000 MHz.

Q: Are both accelerators currently in production?

A: The NVIDIA B300 SXM6 AC has an active production status. The AMD Instinct MI455X has no production status listed in the database.

Specification Differences

The two parts differ across nearly every major specification field. The AMD Instinct MI455X uses a 2 nm process, while the NVIDIA B300 SXM6 AC uses 5 nm. Transistor counts are 320,000 million versus 208,000 million. Die sizes are 2990 mm² versus 1628 mm². Transistor density favors NVIDIA at 127.8M per mm² versus 107.0M per mm².

FP32 and FP16 compute both favor AMD at 157.3 TFLOPS versus 76.99 TFLOPS. Texture rate favors AMD at 2,457.6 GTexel/s versus 1,202.9 GTexel/s. Pixel rate favors NVIDIA at 48.77 GPixel/s versus 0 MPixel/s. The AMD part has 32,768 shading units, 1,024 TMUs, and 0 ROPs. The NVIDIA part has 18,944 shading units, 592 TMUs, and 24 ROPs. The NVIDIA part has 592 tensor cores; the AMD part has none listed.

Memory capacity favors AMD at 432 GB versus 288 GB. Memory type differs: HBM4 versus HBM3e. Bus width is 24,576 bit versus 8,192 bit. Bandwidth is 23.3 TB/s versus 8.19 TB/s. Memory clocks are 1900 MHz (7.6 Gbps effective) versus 2000 MHz (8 Gbps effective).

Power consumption favors NVIDIA at 1100 W TDP versus 2300 W TDP. Suggested PSU is 1500 W versus 2700 W. Slot width is SXM Module versus EAM Module. The NVIDIA part lists a production status of Active; the AMD part does not. Release dates are September 2025 for NVIDIA and July 2026 for AMD. The NVIDIA part lists Server Hopper as predecessor and Server Rubin as successor; the AMD part lists Radeon Instinct as predecessor and no successor.

Head-to-Head Benchmarks

The database contains no direct head-to-head benchmark entries between the AMD Instinct MI455X and the NVIDIA B300 SXM6 AC. The comparison must therefore use the single recorded benchmark for the NVIDIA part and the architectural specifications for both.

The NVIDIA B300 SXM6 AC's Geekbench OpenCL score of 369,831 puts it in the 100th percentile of all GPUs. Its nearest rivals provide context: the NVIDIA B200 scores 345,482, which is 7% lower; the NVIDIA H200 NVL scores 334,891, 10.4% lower; the AMD Instinct MI300X scores 317,994, 16.3% lower; and the NVIDIA L40S scores 295,763, 25% lower. These deltas show the B300 SXM6 AC sits clearly at the top of the measured performance hierarchy.

The AMD Instinct MI455X has no benchmark entries, an average benchmark score of zero, and a 50th percentile ranking. Its nearest rivals list is empty. The database cannot confirm any measured performance for this part.

Compute specifications tell a different story. The AMD part's 157.3 TFLOPS FP32 is 104% higher than the NVIDIA part's 76.99 TFLOPS. Its 23.3 TB/s memory bandwidth is 184% higher than 8.19 TB/s. Its 432 GB capacity is 50% higher than 288 GB. The AMD part also has 2,457.6 GTexel/s texture rate versus 1,202.9 GTexel/s, a 104% advantage.

The NVIDIA part counters with a higher base clock (1665 MHz versus 1000 MHz), a lower boost clock (2032 MHz versus 2400 MHz), a much lower TDP (1100 W versus 2300 W), and the only confirmed production status. It also has a higher transistor density (127.8M per mm² versus 107.0M per mm²) despite using a larger 5 nm node.

The pixel rate comparison is one-sided: the NVIDIA part produces 48.77 GPixel/s while the AMD part produces 0 MPixel/s. The AMD part has zero ROPs, which explains the zero pixel rate. The NVIDIA part has 24 ROPs.

The Verdict

The data supports a split decision based on what the buyer prioritizes. For raw compute specifications, the AMD Instinct MI455X wins decisively. It offers double the FP32 and FP16 throughput, 50% more memory capacity, nearly three times the memory bandwidth, a wider memory bus, and a much larger transistor budget. These figures make it the stronger choice for workloads that scale with raw FLOPs and memory capacity.

For verified, shipping performance, the NVIDIA B300 SXM6 AC wins. It has a recorded Geekbench OpenCL score of 369,831, a 100th percentile ranking, and an active production status. The AMD part has no measured results, sits at the 50th percentile, and lacks a production status. The NVIDIA part also consumes 52% less power (1100 W versus 2300 W), which is a major operational difference.

The nearest rival data strengthens the NVIDIA case. The B300 SXM6 AC leads the B200 by 7%, the H200 NVL by 10.4%, the MI300X by 16.3%, and the L40S by 25%. These are measured deltas, not projections. The AMD MI455X cannot be placed in this ranking because it has no score.

The AMD part targets a different profile: a 2 nm design with 320,000 million transistors, 432 GB of HBM4, and a 2990 mm² die. It is a specification leader with no verification data. The NVIDIA part is a verified leader with a smaller, denser, more power-efficient package.

The verdict from the database: the NVIDIA B300 SXM6 AC is the only part with confirmed performance data and production availability. The AMD Instinct MI455X offers superior specifications on paper, but the absence of benchmark results and production status leaves its real-world standing unconfirmed. Buyers needing a validated accelerator should select the NVIDIA part. Buyers prioritizing maximum memory capacity and compute density on paper should examine the AMD part, provided the lack of measured data is acceptable.