# AMD RX 7900 XTX (24GB) vs RX 9070 XT (16GB) for ROCm Local AI

> **Direct Hardware Verdict**: Across AMD's Radeon lineup, the older RDNA 3 RX 7900 XTX beats the newer RDNA 4 RX 9070 XT for local LLM builders. Although the $599 RX 9070 XT introduces upgraded `gfx1201` WMMA matrix units with hardware FP8 support, its 16GB 256-bit buffer (640 GB/s) overflows completely on Qwen 2.5 Coder 32B (`23.1 GB`), Gemma 4 31B (`21.4 GB`), and Qwen3-Coder 30B-A3B (`20.7 GB`). At ~$740 used, the RX 7900 XTX provides +50% more VRAM and +50% faster memory bandwidth (960 GB/s).

## Contender Specifications
| Metric | AMD Radeon RX 7900 XTX (24GB) | AMD Radeon RX 9070 XT (16GB) |
|---|---|---|
| VRAM Capacity | 24 GB GDDR6 | 16 GB GDDR6 |
| Memory Bandwidth | 384-bit (960 GB/s) | 256-bit (640 GB/s) |
| Typical Price | ~$740 (Used) / ~$929 (Retail) | $599 – $649 (New) |
| Estimated Throughput | ~36 tok/s (32B Q4) / ~68 tok/s (14B Q4) | ~41 tok/s (14B Q4) / Fails 32B Q4 |

## Comparative Model Compatibility Matrix
| Model & Quantization | VRAM Demand | AMD Radeon RX 7900 XTX | AMD Radeon RX 9070 XT |
|---|---|---|---|
| Qwen 2.5 Coder 32B (Q4_K_M, 8k) | 23.1 GB | Runs Comfortably (+0.9GB, ~36 tok/s) | Exceeds VRAM (-7.1GB) |
| Google Gemma 4 31B (Q4_K_M, 8k) | 21.4 GB | Runs Comfortably (+2.6GB) | Exceeds VRAM (-5.4GB) |
| Alibaba Qwen3-Coder 30B-A3B (Q4_K_M) | 20.7 GB | Runs Comfortably (+3.3GB) | Exceeds VRAM (-4.7GB) |
| OpenAI gpt-oss 20B (Q4_K_M, 8k) | 14.4 GB | Runs Comfortably (+9.6GB) | Tight Fit (+1.6GB, Native FP8) |
| Qwen 2.5 14B (Q4_K_M, 32k FP8 KV) | 14.1 GB | Runs Comfortably (+9.9GB) | Runs Comfortably (+1.9GB, ~41 tok/s) |


## Silicon Architecture & Thermal Analysis
This intra-AMD matchup contrasts RDNA 3's brute-force memory configuration against RDNA 4's smarter matrix pipelines. The RX 7900 XTX (`gfx1100`, Navi 31) equips 24GB of 20 Gbps GDDR6 across twelve 32-bit channels (384-bit = 960 GB/s) backed by 96MB of Infinity Cache, yet its first-generation WMMA instructions lack native FP8 math units. By contrast, AMD's monolithic Navi 48 die (`gfx1201`) inside the RX 9070 XT narrows memory down to a 256-bit 640 GB/s interface with 16GB capacity, while overhauling every compute unit with second-generation AI Accelerators supporting native FP8 E4M3/E5M2 and INT4 structured sparsity. Consequently, the RX 9070 XT achieves remarkably responsive prompt prefill on 8B–14B checkpoints and OpenAI `gpt-oss 20B` (`14.43 GB`), whereas any 27B–32B model forces slow PCIe host offloading that the 24GB RX 7900 XTX avoids entirely.

## Tier 1 Free Software Optimization ($0)
Configuring ROCm 6.4+ on Linux? Never copy legacy `HSA_OVERRIDE_GFX_VERSION` environment hacks onto Navi 48 (`gfx1201`), because mismatched wave semantics cause NaN corruption; instead compile `llama-server` natively with `-DGGML_HIP=ON -DAMDGPU_TARGETS=gfx1201` (or `gfx1100` for RX 7900 XTX) alongside `-fa on -ctk q8_0 -ctv q8_0` to stretch context safely.

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