Spark-X2.5: a tiny toolchain fixture

A small, independently initialized random-weight reference model for learning, debugging, and reproducing QFS capture workflows. It is a base/root fixture, not a quantized child.

These weights are untrained, not an assistant, and not a language-quality benchmark. Generated text has no useful semantic quality. No upstream trained weights or training data are implied by an architecture name.

Weight lineage

This checkpoint was initialized directly for an architecture test. It was not fine-tuned from a production model and does not inherit that model's trained weights. Architecture/configuration lineage is documented separately from weight lineage.

Browse the Random Architecture Fixtures collection. A random base may also serve as the common source for an aligned quantization family.

At a glance

Size is serialized artifact size, not runtime RAM or a capacity/performance guarantee. Packed-array element counts are not model parameter counts.

What is actually included

Complete text-only Spark2_5ForCausalLM; 3 sliding/1 full attention, partial RoPE dimensions 16/4, headwise sigmoid gates, GELU gated MLP, tied vocabulary head. Random BF16 only; no learned capabilities, million-token context, accelerator, training, quantized-format, or production-size evidence.

The repository file inventory includes config.json, generation_config.json, tokenizer.json, tokenizer_config.json, build-manifest.json, support.json, upstream-code-audit.json. Exact build/runtime/license inventories are linked below. A file may describe historical provenance without being an executable entry point.

Good community uses—and boundaries

• Learn how to download pinned artifacts, seal a small synthetic token panel, capture hidden states and replay a full vocabulary head.
• Debug model-family adapters, strict tensor loading, storage decoders, or reproducibility tooling without downloading a production-sized checkpoint.
• Reproduce a narrowly scoped result, report an adapter/reader regression, and retain the source, panel and runtime identities needed to explain it.

Not established: trained-model accuracy; useful instruction following; quantizer optimization quality; original production-weight compatibility; GPU/NPU/serving-kernel parity; cross-hardware determinism; long-context behavior outside the recorded panel; throughput or paid-compute admission.

Original-release limitations

• Measured original weights: False
• Not proven: production-size inference; million-token context; GPU/NPU kernels; FP8/MXFP4/quantized formats; training; arbitrary batched/offset position_ids; quality or accuracy; cross-hardware identity
• Upstream context: 1048576
• Upstream dtype: bfloat16
• Upstream parameters: 4112079360

Model family, root dataset and evidence

This model is the base/root of its own random fixture family, not a reproduction of the trained upstream model. The fidelity-root dataset repository is the family reference location. A link is not a claim that registration or publication has completed.

The historical CPU evidence bundle retains two independent captures at first/ and repeat/, plus comparison/. Its repository root is a receipt bundle, not a single canonical QFS dataset. Those recorded same-machine/same-stack forced comparisons reported 0.0 nats on 252 synthetic scored positions; that is not a trained-quality result or a transferable hardware floor. The original detailed receipt and caveats remain authoritative.

Runtime requirements and safe local reproduction

Replay the published evidence without loading a model

This uses QFS's existing NumPy FP64 comparator in a Torch-free environment. It reads the stored hidden states and each side's own head. No model forward, remote model code, GPU, upload or registry mutation is involved. Runtime receipts name the actual backend; last-bit differences from another FP64 implementation are not a new quality claim. Synthetic exact controls remain zero.

Set QFS to a reviewed Quant Fidelity Suite checkout and use Bash:

: "${QFS:?Set QFS to your reviewed QFS checkout}"
WORK=$(mktemp -d)
export OMP_NUM_THREADS=2 MKL_NUM_THREADS=2 OPENBLAS_NUM_THREADS=2
python3.12 -m venv "$WORK/replay-env"
"$WORK/replay-env/bin/pip" install 'numpy==2.5.3' 'huggingface-hub==1.30.0'
"$WORK/replay-env/bin/hf" download malaiwah/qfs-fixture-root-captures-v1 --repo-type dataset \
  --revision f53b204091c988ce4a2161af81886f3018745559 --include 'roots/spark2-5/**' --local-dir "$WORK/evidence"
"$WORK/replay-env/bin/python" "$QFS/bin/fidelity_dataset.py" verify \
  "$WORK/evidence/roots/spark2-5/first" --verify-tensors
"$WORK/replay-env/bin/python" "$QFS/bin/fidelity_dataset.py" verify \
  "$WORK/evidence/roots/spark2-5/repeat" --verify-tensors
"$WORK/replay-env/bin/python" "$QFS/bin/fidelity_dataset.py" compare \
  --reference "$WORK/evidence/roots/spark2-5/first" \
  --candidate "$WORK/evidence/roots/spark2-5/repeat" \
  --out "$WORK/replayed" --device cpu --replay-device numpy --replay-dtype float32 \
  --vocab-chunk 8192 --verify-tensors --self-compare --force-compute

Reconstructed format comparisons are intentionally advisory and normally return exit code 2 while writing a valid receipt. Inspect that receipt; do not silence refusals or interpret an advisory result as a production-quality ranking.

Capture the actual checkpoint

Capture uses a separate pinned Torch CPU environment. The input below is the original token-panel format, not a sealed capture's internal panel/ folder. The native source, tokenizer and model revisions remain explicit. Set AUTHOR to your own HF handle; the dataset repository argument is attribution only and nothing is uploaded by these commands.

: "${AUTHOR:?Set AUTHOR to your Hugging Face handle}"
"$WORK/replay-env/bin/hf" download malaiwah/spark2-5-tiny-random-bf16 --revision c0a57b037007d475ede719e78f4a6ce24f211da0 --local-dir "$WORK/model"
"$WORK/replay-env/bin/hf" download malaiwah/spark2-5-tiny-random-bf16 --revision c0a57b037007d475ede719e78f4a6ce24f211da0 --local-dir "$WORK/source"
"$WORK/replay-env/bin/hf" download malaiwah/qfs-fixture-root-captures-v1 --repo-type dataset \
  --revision f53b204091c988ce4a2161af81886f3018745559 --include 'requirements-capture.txt' --include 'roots/spark2-5/input-panel/**' \
  --local-dir "$WORK/inputs"
python3.12 -m venv "$WORK/capture-env"
"$WORK/capture-env/bin/pip" install -r "$WORK/inputs/requirements-capture.txt"
"$WORK/capture-env/bin/python" "$QFS/bin/fidelity_dataset.py" architectures prepare \
  --architecture spark2-5 --model-dir "$WORK/model" \
  --model-repository malaiwah/spark2-5-tiny-random-bf16 --model-revision c0a57b037007d475ede719e78f4a6ce24f211da0 \
  --panel "$WORK/inputs/roots/spark2-5/input-panel" --tokenizer-root "$WORK/source" \
  --author "$AUTHOR" --dataset-repository "$AUTHOR/spark2-5-tiny-random-bf16-capture" \
  --dataset-id "fidelity--$AUTHOR.spark2-5-tiny-random-bf16" --out "$WORK/workflow" \
  --trust-remote-code --code-repository malaiwah/spark2-5-tiny-random-bf16 --code-revision dd4b081b0a6b042771cbfdaedf82ef345e59f5e9

Inspect workflow.json. This launcher executes its exact capture/verification commands and selects the Torch-free interpreter only for the final comparison:

export OMP_NUM_THREADS=2 MKL_NUM_THREADS=2 OPENBLAS_NUM_THREADS=2
"$WORK/replay-env/bin/python" - "$WORK/workflow/workflow.json" <<'PY'
import json, subprocess, sys
workflow = json.load(open(sys.argv[1]))
for step in workflow["commands"]:
    argv = list(step["argv"])
    if step["step"] == "compare":
        argv[0] = sys.executable
    result = subprocess.run(argv)
    if result.returncode:
        raise SystemExit(result.returncode)
PY

Use the actual root at malaiwah/spark2-5-tiny-fidelity-root-v1@5715a4e51de6af894ac3963cd55d6ebe371dcb5a. The community collection groups models and captures. Custom code, where required above, is explicitly pinned and executed only after your consent; hash verification is provenance, not a sandbox.

Licensing and detailed provenance

• Fixture weights: Apache-2.0; independently randomly initialized
• Reviewed runtime: Apache-2.0; source notices retained
• Upstream weights: Apache-2.0
• Workflow attribution: Inherited MIT notice retained in NOTICE

{
  "generator_sha256": "95295acc504646ed6b3f60bca12e99b880168823a11590146b063b452fb8fb37",
  "lineage": {
    "relationship": "architecture and Apache-2.0 code only; no upstream weights",
    "repository": "XHToken/Spark-X2.5-4B",
    "revision": "5e10fcc0286756aebf7c41dc52c1e42d95c70281"
  },
  "parameter_count": 157504,
  "scope": "Complete text-only Spark2_5ForCausalLM; 3 sliding/1 full attention, partial RoPE dimensions 16/4, headwise sigmoid gates, GELU gated MLP, tied vocabulary head. Random BF16 only; no learned capabilities, million-token context, accelerator, training, quantized-format, or production-size evidence.",
  "seed": 20260907,
  "versions": {
    "safetensors": "0.8.0",
    "tokenizers": "0.23.2",
    "torch": "2.11.0+cpu",
    "transformers": "5.16.1"
  },
  "reviewed_code_pin": {
    "repository": "malaiwah/spark2-5-tiny-random-bf16",
    "revision": "dd4b081b0a6b042771cbfdaedf82ef345e59f5e9"
  }
}