This is the ACE-Step planner, not the audio generator. It produces metadata and 5 Hz semantic audio-code IDs which must be decoded by the ACE-Step semantic detokenizer and supplied to a compatible ACE-Step DiT.

Conversion

Exact 36-layer ACE-Step 4B fine-tuned weights, converted from BF16 to FP16
FP16 activations and KV cache
Five external-data chunks, each below 2 GB
ONNX graph plus weight data: 8,389,939,364 bytes
Browser filename: onnx/model_fp16.onnx

A direct FP16 conversion overflows in the residual stream on the tested runtime. This graph applies a residual scale of 1/256 to the embedding and attention/MLP output projections, and scales residual RMSNorm epsilon by the square of that factor. See conversion-metadata.json.

Validation status

A native ONNX Runtime cached-generation smoke test completed 150 semantic steps with finite logits.
That smoke run produced 142 unique codes and 149 transitions, with no identical adjacent codes.
Against the official MLX checkpoint on one 30-second vocal prompt, first-step top-20 overlap was 60% conditional, 85% unconditional, and 50% after CFG 2.0. Centered logit correlations were 0.993942, 0.990590, and 0.990873.

This is an experimental numerical workaround, not an exact conversion. End-to-end browser audio quality must not be inferred from successful model loading or the finite-logit smoke test.

License and attribution

The source ACE-Step checkpoint is MIT licensed. The repository LICENSE applies to this derivative conversion and ACE-Step attribution is preserved. ONNX Runtime and Transformers.js retain their respective licenses.

emb1ter/ACE-Step-v1.5-5Hz-LM-4B-ONNX-WebGPU

ACE-Step 1.5 5 Hz LM 4B — FP16 ONNX WebGPU

Conversion

Validation status

License and attribution

emb1ter/
ACE-Step-v1.5-5Hz-LM-4B-ONNX-WebGPU