Metal backend: Add Metal int4 quantization support to Parakeet by manuelcandales · Pull Request #17235 · pytorch/executorch

manuelcandales · 2026-02-05T04:18:29Z

This PR adds support for 4-bit weight quantization on the Metal backend for Parakeet TDT model.

Parakeet Export Script (export_parakeet_tdt.py, quantize.py)

Added fpa4w (floating point activation, 4-bit weight) quantization option for encoder and decoder linear layers
Implemented Metal-specific quantization path using torchao's MPS API (UIntxWeightOnlyConfig)
Added validation to ensure fpa4w is only used with Metal backend
Filters out incompatible layers (weights not divisible by 8) during quantization

Documentation (README.md)

Added fpa4w to quantization config table with Metal backend designation
Added example showing Metal 4-bit quantization usage
Reorganized examples to separate CUDA and Metal quantization workflows

CI Integration (export_model_artifact.sh, metal.yml)

Added quantized-int4-metal option to export script with proper backend validation
Updated Metal CI workflow to test int4 quantization specifically with parakeet-tdt model

Dependencies

Bumped torchao pin for latest Metal quantization support

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examples/models/parakeet/quantize.py

examples/models/parakeet/README.md

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github-actions · 2026-02-05T18:36:17Z

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Pull request overview

This PR implements 4-bit weight quantization support for the Parakeet TDT model on the Metal backend using torchao's MPS API. The changes enable Metal-specific quantization while maintaining existing CUDA quantization workflows.

Changes:

Added fpa4w (floating point activation, 4-bit weight) quantization option for Metal backend
Implemented validation to ensure Metal-specific quantization is only used with Metal backend
Updated CI workflows to test Metal int4 quantization with parakeet-tdt model

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
third-party/ao	Updated torchao submodule to version with Metal quantization support
examples/models/parakeet/quantize.py	Added Metal int4 quantization implementation using UIntxWeightOnlyConfig
examples/models/parakeet/export_parakeet_tdt.py	Added fpa4w option and validation for Metal backend requirement
examples/models/parakeet/README.md	Updated documentation with fpa4w config and Metal quantization example
.github/workflows/metal.yml	Added int4 quantization testing for parakeet-tdt model
.ci/scripts/export_model_artifact.sh	Added quantized-int4-metal option with backend validation

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examples/models/parakeet/quantize.py

mergennachin · 2026-02-05T18:56:43Z

@manuelcandales In the README.md, do you wanna add to run "EXECUTORCH_BUILD_KERNELS_TORCHAO=1 TORCHAO_BUILD_EXPERIMENTAL_MPS=1 ./install_executorch.sh" as a prequisite step for int4 metal quantization?

manuelcandales · 2026-02-05T18:59:38Z

@manuelcandales In the README.md, do you wanna add to run "EXECUTORCH_BUILD_KERNELS_TORCHAO=1 TORCHAO_BUILD_EXPERIMENTAL_MPS=1 ./install_executorch.sh" as a prequisite step for int4 metal quantization?

yeah, that's true

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Pull request overview

Copilot reviewed 6 out of 6 changed files in this pull request and generated 4 comments.

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examples/models/parakeet/quantize.py

.github/workflows/metal.yml

.ci/scripts/export_model_artifact.sh

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mergennachin · 2026-02-05T21:24:57Z

examples/models/parakeet/quantize.py

+
+        config = UIntxWeightOnlyConfig(
+            group_size=qlinear_group_size,
+            bitwidth=4,


Update the pin past pytorch/ao#3829, and set

uintx_choose_qparams_algorithm="hqq"

Could be done in a follow-up PR too

yes, that's my plan, to do in follow-up PR

here #17258

manuelcandales added 30 commits January 30, 2026 19:25

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Base automatically changed from gh/manuelcandales/159/head to main February 5, 2026 18:12

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manuelcandales added 3 commits February 5, 2026 14:09

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manuelcandales mentioned this pull request Feb 5, 2026

Metal backend: fix linear_filter in test_modules #17253

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manuelcandales changed the base branch from main to gh/manuelcandales/166/head February 5, 2026 19:45

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