[vincent0426]

🚀 What

Fixes requests failing with a 400 when a model uses the default kind value. For example:

  client.api.post_models(request=CreateModelRequest(
      source=ModelArchiveSource(name="my-model", deployment=...),
  ))

fails with:

  400 Unable to extract tag using discriminator 'kind' [type=union_tag_not_found]

Today it only works if the caller passes kind="model_archive" explicitly, even though the model already defaults to it.
Go SDK always sends the tag, and JS types require it, so only Python is affected.

💻 How

Request bodies are dumped with exclude_unset, so a tag left at its default was dropped. Postprocessing now marks each defaulted tag as set on every instance, so it's always sent.

🔬 Testing

• Added test_defaulted_union_tag_sent, which checks the request body includes kind, and test_defaulted_union_tag_set_on_validated_response. Both fail without this
  change.
• All existing tests pass; poe lint and poe typecheck are clean.
• Checked against the live API: the call above now gets past the tag check and fails only on the missing archive upload (A model-archive push requires the s3_key of an uploaded archive), which is expected.

Note

The spec marks the tag optional with a default, but the server requires it. Happy to close this in favor of a spec/server fix if thats better.

The spec marks the tag optional with a default, but the server requires it. Happy to close this in favor of a spec/server fix if that's better.

"ModelArchiveSourceV1": {
  "required": ["name", "deployment"],
  "properties": {
    "kind": { "const": "model_archive", "default": "model_archive", "type": "string" },
    ...

https://github.com/basetenlabs/baseten-python/blob/3f1347cecbae0fa01244f9437a3ac5d4ac7746b2/scripts/apigen/specs/management.json#L23076-L23120

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🟢 Approval recommended

No active review issues remain for the change preserving defaulted union discriminator tags during serialization.

No open issues 🎉

What changed in this PR

Fixes Python SDK requests that omit defaulted union discriminator tags, causing server-side validation errors. The change preserves these tags during serialization while leaving unrelated unset defaults omitted.

Changes:

• Update model postprocessing to mark defaulted discriminator fields as set.
• Regenerate management API and model configuration models with initialization hooks.
• Add regression tests for request serialization and validated model field tracking.

File	Description
tests/​client/​test_management.py	Tests default tag inclusion and preservation of other unset defaults.
scripts/​apigen/​postprocess.py	Generates initialization hooks that mark defaulted discriminator fields as set.
baseten/​client/​modelconfig/​_models.py	Adds hooks to protocol option models.
baseten/​client/​managementapi/​_models.py	Adds hooks to tagged management API models.

_{Review effort: Balanced}