gguf-tools splicer cannot read the MXFP4 GGUF this repo publishes (unsupported GGML tensor type 39)

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Assessment

Difficulty
1/5
Estimated time
Under an hour
Newbie friendliness
92/100
Issue type
Bug
Clarity
Clearly specified
Activity status
Quiet
Tech stack
c, python

Research direction

Open gguf-tools/mixed/splice_mixed_expert_layers_gguf.py and locate GGML_QUANT_SIZES; compare the MXFP4 values with ds4.c:2052. Run the reported --dry-run splice for layers 25-42, then confirm type 39 is accepted and the selected donor tensors and payload summary complete without the unsupported-type error.

Written by the indexing model from the issue text.

Description

The Flash MXFP4 GGUF (ds4f-mxfp4) cannot be used as a donor or base with gguf-tools/mixed/splice_mixed_expert_layers_gguf.py, because its GGML_QUANT_SIZES table has no entry for type 39.

error: unsupported GGML tensor type 39; add it to GGML_QUANT_SIZES

Everything else in the splicer already handles it correctly — it deliberately does not require base and donor tensor types to match, and it writes each tensor's own ggml_type through. Only the block-size table is missing an entry.

One-line fix, using the values from ds4's own table at ds4.c:2052 ([39] = {"mxfp4", 32, 17}):

 GGML_QUANT_SIZES = {
     ...
     26: (1, 4, "I32"),
+    39: (32, 17, "MXFP4"),
 }

Verified locally with --dry-run, splicing MXFP4 routed experts for layers 25-42 onto the IQ2XXS/Q2_K hybrid base:

selected donor tensors: 54
selected donor types: MXFP4:54
base tensor payload:   90.88 GiB
mixed tensor payload: 107.76 GiB

Motivation, in case it is useful: this produces a quant sized for a single 128 GB Mac. The published Flash quants are 80.8 / 90.9 GiB (fit, leaving ~21 GiB of the 112 GiB wired limit unused) then jump to 145.3 / 153.3 GiB (do not fit). Splicing MXFP4 experts into the upper layers fills that gap at 107.76 GiB.

Happy to open a PR if useful.

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