How do I train and serve MoE models released in MXFP4 (gpt-oss, DeepSeek-V4)?

Solved by experts4bit-qlora · this page in the repository (pinned 605d21e67958, the source of this rendering; latest on main, unpinned; not the source of any fact rendered here)

Install routes

From docs/capabilities.json at the pinned commit.

pip install "experts4bit-qlora[train]"

The loader can decode MXFP4 and re-quantise it to NF4, or load experts for an engine that computes on the released bytes. Loading a model does not establish that every training or residency route supports it. Choose the model and task first.

Model, task and supported entry point

The capability register and its training_support records distinguish these routes:

Two fidelity paths — choose before loading

Only the second path keeps the checkpoint's original expert bytes.

1. Decode, then re-quantise to NF4. The quantising branch of load_moe_4bit_streaming (experts4bit_qlora/loader.py) reads the released blocks and scales through experts4bit_qlora.formats.mxfp4.dequantize_mxfp4 — verified bit-identical to transformers' reference decode in tests/test_mxfp4_dequant.py — and then builds the expert stack in the storage you asked for, NF4 by default: GptOssExperts4bit.from_gptoss(..., quant_type=quant_type) for gpt-oss and DeepseekV4Experts4bit.from_deepseek_v4(..., quant_type=quant_type) for DeepSeek-V4, each of which quantises the decoded stack through Experts4bit.from_float. The resulting base is an NF4 re-quantisation of an exact decode of the release; whether its expert adapters can train depends on the model and path above: the decode is bit-exact, the NF4 that follows it is the quantiser's output, and that — not the release — is the provenance of the served experts. Needs no arena and no kernel package. verify_moe_4bit(model, strict=True) proves the stack is 4-bit, not that it is the released bytes.
2. Native-byte path — retain the released MXFP4 blocks and scales. For the DeepSeek-V4 arena route, relocate the checkpoint's own blocks and scales verbatim into an arena with nvme_arena.bake_expert_tensors (hash-preserving; the manifest's bake_mode records it) and bind it with enable_mxfp4_nvme_residency (serving through mxfp4_grouped's native kernels) or enable_nvme_train_residency on an arena=..., arena_train=True load (training against the arena, gradient checkpointing required). The paged engine's native MXFP4 store — enable_serve_experts_int4 on gpt-oss, which never re-quantises onto the int4 grid — is the all-VRAM form of the same idea. Here the checkpoint's expert bytes are what computes, and provenance is preserved end to end.

Symptoms

• "gpt-oss MXFP4 experts: training and residency" / "QLoRA on an MXFP4 checkpoint" / "MXFP4 expert inference kernel".
• The checkpoint ships gate_up_proj_blocks / gate_up_proj_scales (gpt-oss) or I8 blocks with F8_E8M0 scales (DeepSeek-V4), and a naive from_pretrained materialises them to bf16 first.
• KeyError: 'F8_E8M0' when staging a DeepSeek-V4 arena for training.

Why it happens

MXFP4 (OCP microscaling FP4) stores two e2m1 nibbles per byte in blocks of 32 values sharing one e8m0 power-of-two scale. gpt-oss adds per-expert biases, interleaved gate/up rows and a clamped GLU; DeepSeek-V4 keeps SwiGLU with one-sided and two-sided clamps and stores its dense half as block-scaled FP8 (../DEEPSEEK-V4.md). Re-quantising these experts to a uniform int4 grid fails the quality gate because NF4's levels sit on e2m1's and int4's do not (../SERVING-THROUGHPUT.md).

Which project solves it

experts4bit-qlora owns the model side: formats.mxfp4.dequantize_mxfp4 (verified bit-identical to transformers' reference, tests/test_mxfp4_dequant.py), arch/gptoss.py (biases, de-interleave, clamped GLU, GptOssExperts4bit), arch/deepseek_v4.py (key map, FP8 dense side, _apply_gate epilogue), and the binding engines engines/nvme_experts.py, engines/nvme_train.py and engines/int4_experts.py. grouped-nf4-gemm (GitHub, PyPI) owns the native MXFP4 kernels (mxfp4_grouped, including the decode GEMV), the relocation bake nvme_arena.bake_expert_tensors, and mxfp4_residency. Kernel-level questions belong there; [fast] is the seam.

Install

pip install "experts4bit-qlora[train]"   # minimum/reference training: the loader (decode-then-NF4 path)
pip install "experts4bit-qlora[train,fast]"  # loader plus the native-byte engines used below

Smallest correct example

Needs: GPU + network + the DeepSeek-V4-Flash snapshot on local disk + local NVMe with room for the arena (147 GB of experts, claim e4b.serve.deepseek-v4).

python -c "
from nvme_arena import bake_expert_tensors
from mxfp4_residency import V4_RESIDENCY_KINDS
bake_expert_tensors('/path/to/DeepSeek-V4-Flash', '/nvme/v4.mxarena',
                    name_template='layers.{layer}.ffn.experts.{expert}.{kind}',
                    kinds=V4_RESIDENCY_KINDS)"        # relocation: no re-quantisation

Needs: the same GPU, the [train] and [fast] extras, and the arena baked above.

import torch
from experts4bit_qlora import enable_mxfp4_nvme_residency, load_moe_4bit_streaming

model, cfg = load_moe_4bit_streaming("deepseek-ai/DeepSeek-V4-Flash", "cuda", torch.bfloat16,
                                     r=8, alpha=16, quant_type="nf4", arena="/nvme/v4.mxarena")
n = enable_mxfp4_nvme_residency(model, "/nvme/v4.mxarena",
                                k_slots=cfg.num_experts_per_tok, hot_rows=16)
assert n > 0

DeepSeek-V4 only — experimental arena training: load with arena=..., arena_train=True, then enable_nvme_train_residency(model, arena, hot_rows=<expert count>) with gradient checkpointing enabled (offload-moe-experts-to-cpu-or-nvme.md). The default NF4 loading path needs no arena and does not enable gpt-oss expert training: load_moe_4bit_streaming("openai/gpt-oss-20b", ...) then verify_moe_4bit(model, strict=True).

Expected result

enable_mxfp4_nvme_residency returns the number of MoE modules bound (one per layer); a model loaded with arena= has its experts on meta and cannot run until an engine is bound. enable_nvme_train_residency returns the number of modules moved and refuses an undersized hot_rows. For the NF4 path, verify_moe_4bit(model, strict=True) returns without raising. The CPU spec for the MXFP4 training arena — layout resolution, staging into MXFP4-declared buffers, numerics against an oracle decoded from the source bytes — is tests/test_mxfp4_arena_train.py.

Supported scope

• Families: gpt-oss (per-expert biases, clamped GLU, interleaved rows) and DeepSeek-V4 Flash / Pro (clamped SwiGLU, FP8 dense side).
• Arena provenance: a relocation bake is hash-preserving, so the served bytes are the checkpoint's own; a quantize-at-bake NF4 arena is bit-identical to the quantiser's output, not to the release. The manifest records bake_mode.
• Version floors, all from pyproject.toml: the fast extra's floor is grouped-nf4-gemm >= 0.43.0 at this commit (validated by CI). Two lower feature floors are recorded in its comment ladder and sit below the current floor: training on an MXFP4 arena landed in grouped-nf4-gemm 0.12.0 (the F8_E8M0 scale tag; below it check_arena_geometry raises KeyError), and the MXFP4 grouped kernels' 64-bit expert offset (grouped-nf4-gemm#205) in 0.14.0.
• Environment: Linux, NVIDIA CUDA sm_80 or newer, Triton (Linux-only); CI tests Python 3.11.

Limitations

• A uniform int4 grid cannot serve MXFP4 experts. For gpt-oss, enable_serve_experts_int4 never re-quantises onto the int4 grid; it installs the native MXFP4 store served through mxfp4_grouped's decode GEMV. That store is opt-in and single-stream-oriented (batched rows fall back to NF4 when the stacks are kept via E4B_INT4_KEEP_NF4=1), and its quality claim is fidelity to the shipped bytes (0.0019 nats/token from their dequantized form, e4b.serve.p44.gptoss.store-r12.kl-vs-bf16.2026-09-19), not downstream quality.
• enable_fast skips MXFP4-arena modules on purpose; their forward is wired by nvme_experts.
• enable_mxfp4_nvme_residency refuses ExpertsLoRA-wrapped modules: under the arena loader the base buffers are on meta, and binding would discard the adapter. Serve from the arena or train against it, not both on one load.
• ExpertsLoRA trains gpt-oss's biased, clamped experts on its unfused reference loop only, opt-in through E4B_GPTOSS_EXPERT_LORA=1; its cost against a fused route is unmeasured.
• DeepSeek-V4's full-width resident load does not fit a small card; use the arena path.
• A bf16 checkpoint's training arena is an NF4 quantise-at-bake (grouped-nf4-gemm's nvme_bake_nf4, offload-moe-experts-to-cpu-or-nvme.md), not the native-byte path; e4b.open.tr2-repro-gap (reproducing the TR2 training receipt) stays open in the register.
• Training on an MXFP4 arena has a CPU spec and a bench directory (bench/mxfp4-arena-train/) but no entry in the claims register: a capability, not a measured result.

Related

• offload-moe-experts-to-cpu-or-nvme.md · serve-large-moe-on-a-consumer-gpu.md · bitsandbytes-moe-load-in-4bit-still-ooms.md · qlora-fused-moe-experts.md
• ../DEEPSEEK-V4.md · ../RESIDENCY-ENGINES.md · ../SERVING-THROUGHPUT.md · ../STATUS.md

Evidence

Register: ../claims.json.

• e4b.serve.gptoss.loader-faithful — measured; the numeric receipt is in a private audit tree (evidence_private), the probe script is in-repo: MXFP4 dequant bit-identical to the reference, served expert path faithful to HF's reference math.
• e4b.serve.deepseek-v4 — measured: DeepSeek-V4-Flash loads and generates with its experts served from an on-disk arena.
• e4b.serve.informed-hot-sets — measured: on V4-Flash's arena, profile-ranked hot sets beat by-index at identical VRAM.
• e4b.serve.buildout.gptoss.b1.5090.2026-09-04 — measured: gpt-oss-20b's licensed stack is NF4 experts plus folds; the native MXFP4 store's row is speed with the quality gate open.
• Training on an MXFP4 arena: this page describes a capability; it carries no performance claim.

Common wrong approaches

• Re-quantising an MXFP4 checkpoint to NF4 or int4: a uniform int4 grid cannot hold the e2m1 levels.
• Ranking an exact MXFP4 arm against a noisy NF4 arm by raw-text perplexity on gpt-oss: the noisier arm scores better there.

Source and freshness

This page is a rendering of docs/solutions/mxfp4-moe-training-and-residency.md at commit 605d21e67958 (sha256 1a4bbae245d351bc…). Numbers are never copied here: every measured statement cites a claim ID in docs/claims.json at that commit. Repository-relative links resolve to this site's pages where the document is published and to the pinned commit otherwise.