RX 7900 XT vs RX 6700 XT for local AI

VRAM, bandwidth, gfx

Which 35B quants fit

Qwen3.6-35B-A3B on llama.cpp, f16 KV. Totals are calculator estimates. Speed is measured only on the R9700 cells that already exist; everything else stays not measured. UD-Q3_K_XL is always a labeled estimate.

Weights file Estimate: total_params × 6.56 bpw (nominal GGUF Q6_K; UD-Q6_K_XL uses the same bucket) / 8. Active params do not shrink the file.. Same GGUF on both cards.

System RAM

When a house 35B Q4 file does not fit, the spill is system RAM. Shopper lines stay Minimum system RAM needed and RAM needed at full context for Qwen3.6-35B-A3B at llama.cpp, Q4_K_M, 32K selected and the model’s full context. Estimate unless a measured R9700 card overlays the kit. If both sides fit, those labels still name the calculator lines if you raise context or a larger quant.

ROCm and Vulkan

1. Note 1

   llama.cpp first

   Consumer RDNA 2 on this list is unofficial on the current Radeon ROCm row (W6800 gfx1030 is the official workstation listing). Prefer Vulkan llama.cpp if HIP is angry. Ollama and vLLM are not the house path on these sheets.

2. Note 2

   Different gfx family packages

   RX 7900 XT needs the gfx1100 family package (gfx1100. 20 GB is a real bracket — run the calculator before you assume a 35B Q5 fit.) RX 6700 XT needs gfx1031 (Navi 22 / RX 67xx is gfx1031. Not the official gfx1030 W6800 row on the current Radeon ROCm matrix. Community HIP/Vulkan paths exist. Prefer Vulkan llama.cpp if HIP is angry. See the gfx1031 HSA_OVERRIDE note.) Do not mix those pins.

3. Note 3

   Cited support rows

   RX 7900 XT: official — gfx1100. 20 GB is a real bracket — run the calculator before you assume a 35B Q5 fit. RX 6700 XT: unofficial — Navi 22 / RX 67xx is gfx1031. Not the official gfx1030 W6800 row on the current Radeon ROCm matrix. Community HIP/Vulkan paths exist. Prefer Vulkan llama.cpp if HIP is angry. See the gfx1031 HSA_OVERRIDE note.

Cited rows: ROCm 10.1.0 compatibility matrix and Linux system requirements. More gfx notes on /rocm/gfx.

Plain-English pick

• Chat

  Neither card holds house 35B Q4–Q6 in VRAM on the calculator. Chat still works with RAM offload — read Minimum system RAM needed and RAM needed at full context below — or a listed UD-Q3_K_XL estimate. RX 7900 XT has the larger memory class on this pair.

• Coding agents

  Both sides offload house 35B Q4. A coding agent will share that RAM spill. Minimum system RAM needed and RAM needed at full context are the shopper lines. We do not invent a tokens-per-tool figure.

• Long context

  KV grows with context. Q4 at 32K spills on RX 7900 XT and spills on RX 6700 XT on the calculator. Read the long-context guide for the measured R9700 128K–262K cards. We do not invent a 128K tok/s here.

• Image gen

  Image gen on AMDai is ComfyUI / HIP PyTorch, not llama.cpp. RX 7900 XT is the 16 GB discrete class; RX 6700 XT is the 12 GB discrete class. Seconds-per-image stay not yet measured by AMDai. Start smaller (SD 1.5) on 8 / 12 / 16 GB class cards. Flux-class is tighter than SDXL. Size the checkpoint on the image-gen guide — do not copy a tok/s from the LLM table.

Check price

Affiliate hops only. No live or invented street price. Same disclosure as every other sheet.