AMD Instinct MI308X vs AMD Instinct MI455X Comparison

Head-to-Head Benchmarks

The recorded database contains no direct head-to-head benchmark results for the AMD Instinct MI308X and the AMD Instinct MI455X. Both accelerators have an average benchmark score of zero and a percentile rank of 50 against all GPUs. This indicates that neither part has been subjected to the standard benchmark suite used by the database, so no direct numerical comparison of application performance can be drawn from measured data.

The raw compute specifications, however, provide a clear scaling picture. The MI455X delivers 157.3 TFLOPS of FP32 throughput, which is 92.5% higher than the MI308X's 81.72 TFLOPS. The FP16 figures are identical in ratio: 157.3 TFLOPS versus 81.72 TFLOPS, with both parts operating at a 1:1 FP16 to FP32 ratio. These numbers represent theoretical peak throughput, not measured application performance, but they indicate a substantial generational uplift in raw compute capability.

Memory bandwidth shows an even larger divergence. The MI455X reaches 23.3 TB/s across a 24576-bit HBM4 interface, compared to the MI308X's 5.32 TB/s across an 8192-bit HBM3 bus. This is a 4.38x increase in memory bandwidth, a factor that heavily influences workloads with large working sets or memory-bound kernels. The MI455X also carries 432 GB of memory versus 192 GB on the MI308X, a 2.25x capacity increase.

Texture rate favors the MI308X slightly: 2,553.6 GTexel/s versus 2,457.6 GTexel/s on the MI455X, despite the latter having more shading units. This occurs because the MI455X has 1024 TMUs compared to 1216 on the MI308X. Pixel rate is listed as 0 MPixel/s for both, as neither part has ROPs or display outputs.

Clock speeds also differ. The MI308X has a base of 1000 MHz and a boost of 2100 MHz, while the MI455X has the same 1000 MHz base but a boost of 2400 MHz. Memory clocks are 1300 MHz (5.2 Gbps effective) on the MI308X and 1900 MHz (7.6 Gbps effective) on the MI455X.

Where Each One Wins

Based on the specification data, the MI455X wins decisively in every metric that matters for high-performance compute workloads. Its FP32 throughput is nearly double, memory bandwidth is over four times higher, and memory capacity is more than double. For large-scale AI training, inference, or scientific simulation where memory bandwidth limits scaling, the MI455X is the clear choice.

The MI308X does hold one narrow advantage: texture fill rate. At 2,553.6 GTexel/s, it exceeds the MI455X by 96 GTexel/s because of its higher TMU count. However, texture rate matters primarily in graphics rendering, and both parts have no display outputs, no rasterization hardware, and no graphics API support (DirectX, OpenGL, and Vulkan are all listed as N/A). The texture rate advantage is therefore largely irrelevant for the intended accelerator workloads.

The MI308X also has a lower power envelope at 750 W TDP versus 2300 W on the MI455X, and a lower suggested PSU rating of 1150 W versus 2700 W. This makes the MI308X easier to integrate into existing infrastructure, but the performance gap is substantial. The MI455X is designed for a different class of system, as indicated by its EAM Module slot width versus the OAM Module on the MI308X.

For memory-bound workloads, the MI455X's 23.3 TB/s bandwidth is the defining feature. The 432 GB capacity allows larger models or datasets to reside on-device, avoiding host memory transfers. The MI308X, with 192 GB and 5.32 TB/s, is still a capable accelerator for many tasks but will hit capacity or bandwidth limits earlier on the largest problems.

Architecture Differences

The MI308X uses the Aqua Vanjaram chip built on CDNA 3.0 architecture, manufactured on a 5 nm process at TSMC. It contains 153,000 million transistors on a 1017 mm² die, yielding a transistor density of 150.4 million per mm². The MI455X uses the MI450 256CU chip built on CDNA 5.0 architecture, manufactured on a 2 nm process at TSMC. It contains 320,000 million transistors on a 2990 mm² die, giving a transistor density of 107.0 million per mm².

The process node shrink from 5 nm to 2 nm is significant, but the MI455X die is nearly three times larger, which explains the lower transistor density. The larger die allows for 32768 shading units on the MI455X versus 19456 on the MI308X, a 68.4% increase in compute unit count. The MI455X also has fewer TMUs (1024 versus 1216), which is an unusual trade-off but consistent with its compute-first design.

Memory architecture differs substantially. The MI308X uses HBM3 with an 8192-bit bus, while the MI455X uses HBM4 with a 24576-bit bus. The 3x wider bus, combined with the higher memory clock, produces the 4.38x bandwidth advantage. Memory type generation also matters: HBM4 is a newer standard with higher per-pin data rates.

The bus interface differs as well. The MI308X uses PCIe 5.0 x16, while the MI455X uses PCIe 6.0 x16. For accelerator-to-host communication, the newer PCIe generation doubles the per-lane data rate, which can reduce transfer bottlenecks when moving data between system memory and the accelerator.

Both parts have no display outputs, no ROPs, no ray tracing cores, and no tensor cores listed. They are pure compute accelerators with no graphics pipeline support. The MI308X was released on 2023-12-05, while the MI455X has a release date of 2026-07-22. Both share the same predecessor, Radeon Instinct, and neither has a successor listed.

Power architecture also differs. The MI308X has a TDP of 750 W and a suggested PSU of 1150 W, while the MI455X has a TDP of 2300 W and a suggested PSU of 2700 W. Neither card uses power connectors, as they are designed for modular server platforms that deliver power through the board. The MI308X uses an OAM Module slot, while the MI455X uses an EAM Module slot.

FAQ

Q: Which accelerator has higher FP32 compute throughput?

A: The MI455X delivers 157.3 TFLOPS of FP32 performance, compared to 81.72 TFLOPS on the MI308X. This represents a 92.5% increase in raw floating-point throughput.

Q: How much memory bandwidth does each accelerator provide?

A: The MI455X provides 23.3 TB/s of bandwidth across a 24576-bit HBM4 interface. The MI308X provides 5.32 TB/s across an 8192-bit HBM3 interface. The MI455X's bandwidth is 4.38 times higher.

Q: What are the memory capacities of these two accelerators?

A: The MI455X has 432 GB of HBM4 memory, while the MI308X has 192 GB of HBM3 memory. The MI455X offers 2.25 times more on-device capacity.

Q: Do either of these cards support graphics rendering?

A: No. Both have no display outputs, no ROPs, and report N/A for DirectX, OpenGL, and Vulkan APIs. They are compute-only accelerators with 0 MPixel/s pixel rate.

Q: Which card has a higher boost clock?

A: The MI455X boosts to 2400 MHz, while the MI308X boosts to 2100 MHz. Both have the same 1000 MHz base clock.

Q: What are the power requirements for each?

A: The MI308X has a TDP of 750 W and a suggested PSU of 1150 W. The MI455X has a TDP of 2300 W and a suggested PSU of 2700 W. Neither uses external power connectors.

The Verdict

The data shows a clear generational leap. The MI455X outperforms the MI308X in every meaningful compute metric: 92.5% higher FP32, 4.38x higher memory bandwidth, and 2.25x more memory capacity. It also uses a newer architecture (CDNA 5.0 versus CDNA 3.0), a smaller process node (2 nm versus 5 nm), and a faster bus interface (PCIe 6.0 versus PCIe 5.0).

The MI308X retains advantages only in texture rate (2,553.6 GTexel/s versus 2,457.6 GTexel/s), lower power draw (750 W versus 2300 W), and lower PSU requirement (1150 W versus 2700 W). For deployments where power budget or existing power infrastructure is a hard constraint, the MI308X remains viable. Its 192 GB memory and 5.32 TB/s bandwidth still position it as a capable accelerator for many large models.

For new deployments targeting the largest AI training runs, inference at scale, or memory-intensive scientific computing, the MI455X is the superior choice on every performance axis. The 432 GB capacity and 23.3 TB/s bandwidth directly address the two most common bottlenecks in accelerator workloads. The 2300 W TDP and 2700 W suggested PSU indicate that system integration must be planned accordingly, but the performance data justifies the infrastructure investment.

Neither part has any benchmark scores recorded in the database, so these conclusions rest on specification-level analysis rather than measured application performance. The theoretical peak figures indicate that the MI455X is the faster part, and the architectural improvements (CDNA 5.0, HBM4, PCIe 6.0) confirm that it is designed to handle workloads that would strain or exceed the MI308X's capabilities.

Specification Differences

The following fields differ between the two accelerators:

| Field | MI308X | MI455X |

|-------|--------|--------|

| Chip | Aqua Vanjaram | MI450 256CU |

| Architecture | CDNA 3.0 | CDNA 5.0 |

| Process Node | 5 nm | 2 nm |

| Transistors | 153,000 million | 320,000 million |

| Die Size | 1017 mm² | 2990 mm² |

| Transistor Density | 150.4M / mm² | 107.0M / mm² |

| Boost Clock | 2100 MHz | 2400 MHz |

| Memory Clock | 1300 MHz (5.2 Gbps effective) | 1900 MHz (7.6 Gbps effective) |

| Memory Size | 192 GB | 432 GB |

| Memory Type | HBM3 | HBM4 |

| Memory Bus Width | 8192 bit | 24576 bit |

| Memory Bandwidth | 5.32 TB/s | 23.3 TB/s |

| Shading Units | 19456 | 32768 |

| TMUs | 1216 | 1024 |

| Texture Rate | 2,553.6 GTexel/s | 2,457.6 GTexel/s |

| FP32 | 81.72 TFLOPS | 157.3 TFLOPS |

| FP16 | 81.72 TFLOPS (1:1) | 157.3 TFLOPS (1:1) |

| TDP | 750 W | 2300 W |

| Slot Width | OAM Module | EAM Module |

| Suggested PSU | 1150 W | 2700 W |

| Bus Interface | PCIe 5.0 x16 | PCIe 6.0 x16 |

| Release Date | 2023-12-05 | 2026-07-22 |

Fields that are identical include the base clock (1000 MHz), pixel rate (0 MPixel/s), ROPs (0), display outputs (no outputs), APIs (all N/A), power connectors (none), manufacturer (AMD), generation (Instinct MIx), predecessor (Radeon Instinct), and the absence of a successor.