PT2 Archive Spec

Created On: Jul 16, 2025 | Last Updated On: Sep 09, 2025

The following specification defines the archive format which can be produced through the following methods:

• torch.export through calling torch.export.save()

• AOTInductor through calling torch._inductor.aoti_compile_and_package()

The archive is a zipfile, and can be manipulated using standard zipfile APIs.

The following is a sample archive. We will walk through the archive folder by folder.

.
├── archive_format
├── byteorder
├── .data
│   ├── serialization_id
│   └── version
├── data
│   ├── aotinductor
│   │   └── model1
│   │       ├── cf5ez6ifexr7i2hezzz4s7xfusj4wtisvu2gddeamh37bw6bghjw.kernel_metadata.json
│   │       ├── cf5ez6ifexr7i2hezzz4s7xfusj4wtisvu2gddeamh37bw6bghjw.kernel.cpp
│   │       ├── cf5ez6ifexr7i2hezzz4s7xfusj4wtisvu2gddeamh37bw6bghjw.wrapper_metadata.json
│   │       ├── cf5ez6ifexr7i2hezzz4s7xfusj4wtisvu2gddeamh37bw6bghjw.wrapper.cpp
│   │       ├── cf5ez6ifexr7i2hezzz4s7xfusj4wtisvu2gddeamh37bw6bghjw.wrapper.so
│   │       ├── cg7domx3woam3nnliwud7yvtcencqctxkvvcafuriladwxw4nfiv.cubin
│   │       └── cubaaxppb6xmuqdm4bej55h2pftbce3bjyyvljxbtdfuolmv45ex.cubin
│   ├── weights
│   │  ├── model1_weights_config.json
│   │  ├── model2_weights_config.json
│   │  ├── weight_0
│   │  ├── weight_1
│   │  ├── weight_2
│   └── constants
│   │  ├── model1_constants_config.json
│   │  ├── model2_constants_config.json
│   │  ├── tensor_0
│   │  ├── tensor_1
│   │  ├── custom_obj_0
│   │  ├── custom_obj_1
│   └── sample_inputs
│       ├── model1.pt
│       └── model2.pt
├── extra
│   └── ....json
└── models
    ├── model1.json
    └── model2.json

Contents

Archive Headers

• archive_format declares the format used by this archive. Currently, it can only be “pt2”.

• byteorder. One of “little” or “big”, used by zip file reader

• /.data/version contains the archive version. (Notice that this is neither export serialization’s schema version, nor Aten Opset Version).

• /.data/serialization_id is a hash generated for the current archive, used for verification.

AOTInductor Compiled Artifact

Path: /data/aotinductor/<model_name>-<backend>/

AOTInductor compilation artifacts are saved for each model-backend pair. For example, compilation artifacts for the model1 model on A100 and H100 will be saved in model1-a100 and model1-h100 folders separately.

The folder typically contains

• <uuid>.wrapper.so: Dynamic library compiled from .cpp.

• <uuid>.wrapper.cpp: AOTInductor generated cpp wrapper file.

• <uuid>.kernel.cpp: AOTInductor generated cpp kernel file.

• *.cubin: Triton kernels compiled from triton codegen kernels

• <uuid>.wrapper_metadata.json: Metadata which was passed in from the aot_inductor.metadata inductor config

• (optional) <uuid>.json: External fallback nodes for custom ops to be executed by ProxyExecutor, serialized according to ExternKernelNode struct. If the model doesn’t use custom ops/ProxyExecutor, this file would be omitted.

Weights

Path: /data/weights/*

Model parameters and buffers are saved in the /data/weights/ folder. Each tensor is saved as a separated file. The file only contains the raw data blob, tensor metadata and mapping from model weight FQN to saved raw data blob are saved separately in the <model_name>_weights_config.json.

Constants

Path: /data/constants/*

TensorConstants, non-persistent buffers and TorchBind objects are saved in the /data/constants/ folder. Metadata and mapping from model constant FQN to saved raw data blob are saved separately in the <model_name>_constants_config.json

Sample Inputs

Path: /data/sample_inputs/<model_name>.pt

The sample_input used by torch.export could be included in the archive for downstream use. Typically, it’s a flattened list of Tensors, combining both args and kwargs of the forward() function.

The .pt file is produced by torch.save(sample_input), and can be loaded by torch.load() in python and torch::pickle_load() in c++.

When the model has multiple copies of sample input, it would be packaged as <model_name>_<index>.pt.

Models Definitions

Path: /models/<model_name>.json

Model definition is the serialized json of the ExportedProgram from torch.export.save, and other model-level metadata.

Multiple Models

This archive spec supports multiple model definitions coexisting in the same file, with <model_name> serving as a unique identifier for the models, and will be used as reference in other folders of the archive.

Lower level APIs like torch.export.pt2_archive._package.package_pt2() and torch.export.pt2_archive._package.load_pt2() allow you to have finer-grained control over the packaging and loading process.