AMD MI400 + Helios Rack: 432GB HBM4 + 260 TB/s UALoF Open Interconnect

In 2026, AMD launched MI400 (CDNA Next) + Helios 72-GPU rack, AMD's flagship solution targeting NVIDIA NVL72. This article analyzes MI400's key specifications, the Helios rack's open interconnect (UALoF) strategy, and a comparison with Rubin R200.

MI400 Core Specifications

Item	MI400	Previous Gen MI350	Improvement
Architecture	CDNA Next	CDNA 4	New generation
Process	TSMC 3nm / 2nm	TSMC 3nm	More advanced
Memory	432 GB HBM4	288 GB HBM3e	1.5×
Memory bandwidth	19.6 TB/s	8 TB/s	2.45×
FP4 Tensor (dense)	40 PFLOPS	20 PFLOPS	2×
FP8 Tensor (dense)	20 PFLOPS	10 PFLOPS	2×
TDP	~1,000 W	~1,000 W	unchanged
PCIe	Gen 6	Gen 5	2×
Release date	2026	2025	—

432 GB HBM4 = the world's largest single-card memory. Compared to NVIDIA Rubin R200's 288 GB, that's 50% more. This is a key advantage for very-large model inference.

CDNA Next Architecture Highlights

Key evolutions in AMD CDNA Next:

1. FP4 matrix engine: native MXFP4 / NVFP4 support
2. Enhanced sparse compute: 2× sparse throughput over CDNA 4
3. Larger Infinity Cache: ~512 MB
4. Heterogeneous scheduler: CPU+GPU co-optimization (EPYC Venice co-processing)

Helios Rack: AMD's NVL72 Response

Helios is AMD's rack-level solution, targeting NVIDIA GB300 NVL72 / Rubin NVL72:

Item	Helios Rack	NVIDIA Rubin NVL72
GPU count	72 MI400	72 Rubin
CPU count	36 EPYC Venice	36 Vera
Total HBM	31.1 TB HBM4	20.7 TB HBM4
Scale-up interconnect	UALoF 260 TB/s	NVLink 6 252 TB/s
Scale-out network	Pensando Vulcano 800G	ConnectX-9 14.4 Tbps
FP4 compute (dense)	2.88 EFLOPS	3.6 EFLOPS (sparse)
FP4 dense converted	2.88 EF	1.8 EF
TDP (rack)	~80 kW	~130 kW
Cooling	Liquid required	Liquid required

AMD Helios surpasses NVIDIA Rubin NVL72 in dense compute (2.88 vs 1.8 EFLOPS). But NVIDIA's sparse compute doubles to 3.6 EFLOPS, so it's "a trade-off of advantages".

UALoF: Open Interconnect Challenges NVLink

Ultra Accelerator Link (UALoF / UALink) is an open standard scale-up interconnect protocol jointly driven by AMD + Broadcom + Intel:

• Goal: replace NVLink's single-vendor closed ecosystem
• 2026 debut: AMD Helios 72-GPU rack
• Future: Intel Jaguar Shores, AWS UltraServers

UALoF key features:

Feature	UALoF	NVLink 6
Standardization	Open standard	NVIDIA proprietary
Bandwidth (rack-level)	260 TB/s	252 TB/s
Vendors	AMD/Broadcom/Intel	NVIDIA only
Ecosystem	ROCm + Open	CUDA only
Future scalability	High	Limited

UALoF's real threat is not the present, but the future. If UALoF can build a complete ecosystem within 2-3 years, NVIDIA's closed interconnect advantage will be weakened.

ROCm 8 Software Ecosystem

AMD continues to invest in ROCm:

• ROCm 7.x (2025 GA): PyTorch / JAX / Triton fully optimized
• ROCm 8.x (2026): CDNA Next debut, full FP4 / FP8 support
• vLLM 0.7+ (AMD-SGLang optimized version)
• AMD Composable Kernel (CK): analogous to CUDA Cores, open source
• MIGraphX / ONNX-Runtime: inference engine
• Infinity Hub: AMD official reference implementation

Deployment Recommendations

Scenario	Recommended Configuration
700B+ model training	Helios rack (72 GPU, single rack can run 700B models)
1T+ mega-model training	Multi-rack + UALoF cross-rack interconnect
Ultra-low-latency inference	MI400 + FP4 + vLLM/AMD-SGLang
Scientific computing	MI400 + ROCm 7/8 + OpenMP
Multimodal generation	MI400 (432GB full retention)
Preferring open ecosystem	UALoF + ROCm 8 (avoid NVIDIA lock-in)

MI400 vs Rubin R200 (Flagship Comparison)

Metric	MI400 (CDNA Next)	Rubin R200
Memory	432 GB HBM4 ✅	288 GB HBM4
Memory bandwidth	19.6 TB/s	22 TB/s ✅
FP4 dense	40 PF ✅	25 PF
FP8 dense	20 PF	12.5 PF
Per-GPU interconnect	UALoF (open) ✅	NVLink 6 (closed)
Per-GPU network	Pensando 800G	ConnectX-9 14.4 Tbps ✅
CPU	EPYC Venice	Vera ARM 88-core ✅
Ecosystem	ROCm 8 (open source) ✅	CUDA 13 (mature) ✅
Standardization	UALoF ✅	NVLink ❌
TDP	1,000 W ✅	1,800 W

AMD advantages: large memory, FP4 dense compute lead, open interconnect, lower power NVIDIA advantages: HBM bandwidth, CPU integration, DC network, CUDA ecosystem

Detailed Product Pages

• AMD MI400 Full Specs
• AMD MI350 (Previous Gen)
• NVIDIA Rubin R200 (Contemporary)
• AMD Helios Rack Documentation
• Future Roadmap

Summary

AMD MI400 + Helios is AMD's strongest counterattack in AI compute:

1. CDNA Next + 432 GB HBM4 matches NVIDIA on hardware specs
2. Helios 72-GPU rack even surpasses NVIDIA NVL72 in dense compute
3. UALoF open interconnect is a real threat to NVLink's closed ecosystem
4. ROCm 8 ecosystem continues to improve, but still needs time

In 2026, AMD is the only GPU vendor capable of challenging NVIDIA head-on.