The hard part of a new transformers-family model — the patchgen config, parallel plan, MoE weight conversion, __init__.py registration, codegen — lives in /veomni-patchgen-model. This skill is the wrapper around it: it decides what you are adding, then hands off, then does the config, trainer and data work that patchgen does not cover.

Before You Start: Create a Plan

Track the phases with whatever todo/plan tool the running agent provides:

Phase 1: Analyze HF model             -> in_progress
Phase 2: Modeling (/veomni-patchgen-model)  -> pending
Phase 3: Write training config         -> pending
Phase 4: Integrate with trainer        -> pending
Phase 5: Test and document             -> pending

Phase 1: Analyze HuggingFace Model

1. Identify the model on HuggingFace. Read its config.json, modeling_*.py, and any processor configs.

2. Determine model category:

   • Text-only LLM -> veomni/models/transformers/<model_name>/
   • Vision-Language -> veomni/models/transformers/<model_name>/ + veomni/data/multimodal/
   • MoE model -> additional veomni/distributed/moe/ integration
   • Diffusion model -> veomni/models/diffusers/<model_name>/

3. Check existing similar models: Find the closest existing model in veomni/models/transformers/ and use it as a reference. E.g., if adding a new Qwen variant, reference qwen3/ or qwen3_vl/.

4. Identify required patches: VeOmni uses a patchgen system (veomni/patchgen/) to generate model patches from the HuggingFace modeling. Check whether a sibling model already has a config you can extend via name_map — that is usually the difference between a 60-line config and a 1000-line one.

5. Compare checkpoint keys against the supported upstream version and any existing VeOmni model. Apply the decision rule below before resolving a mismatch.

Checkpoint key conflicts require a user decision

When upstream model, VeOmni model, or checkpoint parameter keys disagree, show the concrete old/new keys and explain the impact on weight loading, export, and optimizer/DCP resume. Ask the user how to resolve the conflict before implementing a rename, alias, or compatibility mapping. Do not silently retain an obsolete model hierarchy just to preserve checkpoint keys.

If the user has already chosen a resolution in the current task, apply it without asking again. When that choice is to follow current upstream keys, keep those keys in the model and handle approved legacy-key conversion in the checkpoint layer. Verify the chosen direction with strict loading and checkpoint round-trip tests; do not hide mismatches with strict=False.

Phase 2: Modeling — hand off to /veomni-patchgen-model

1. Create the model directory: veomni/models/transformers/<model_name>/.

2. Switch to /veomni-patchgen-model. It owns the whole modeling surface — the <model_name>_{gpu,npu}_patch_gen_config.py files, ExtraParallel parallel_plan.py, any required MoE checkpoint_tensor_converter.py, __init__.py registration, make patchgen, and the model-level test cases — with the working examples and the pitfalls that cost the most time. Do not re-derive it from this file.

   Note that parallel_plan.py is not an FSDP wrapping policy: FSDP2 wraps generically in build_parallelize_model(), and ParallelPlan (veomni/distributed/parallel_plan.py) only describes ExtraParallel sharding, such as expert parallelism or embedding sharding. Add a plan whenever the model uses ExtraParallel, including dense models that shard embeddings; a model without ExtraParallel does not need one.

3. Exception — non-transformers architectures. Diffusion models under veomni/models/diffusers/<model_name>/, and the flux / movqgan / wan directories, have no generated/ output and no patchgen config: they patch through device_patch.py or direct modeling. Copy the closest existing one and skip to Phase 3.

Come back here once the model loads and its registry / patch tests pass.

Phase 3: Write Training Config

1. Model config: Create configs/model_configs/<model_family>/<ModelName>.json matching HuggingFace format.

2. Training config: Create YAML in the appropriate directory:

   • Text: configs/text/<model_name>.yaml
   • Multimodal: configs/multimodal/<model_name>/<model_name>.yaml
   • DiT: configs/dit/<model_name>.yaml

3. Config must include: model path, data config, optimizer settings, parallelism config, checkpoint settings.

4. Verify against existing configs — match the structure of similar model configs.

Phase 4: Integrate with Trainer

1. Verify the model works with the appropriate trainer:

   • Text -> TextTrainer (veomni/trainer/text_trainer.py)
   • VLM -> VLMTrainer (veomni/trainer/vlm_trainer.py)
   • DiT -> DitTrainer (veomni/trainer/dit_trainer.py)

2. If the model needs custom data preprocessing:

   • Add transform in veomni/data/data_transform.py or veomni/data/multimodal/
   • Register the transform for the model

3. If the model needs custom collator logic:

   • Extend veomni/data/data_collator.py

4. VLM only — multimodal metadata precompute: to keep the ViT forward free of host-device CUDA syncs, derive ViT cu_seqlens / max_seqlen in the collator rather than the forward. Follow the checklist in .agents/knowledge/multimodal_metadata.md ("Adding the hook to a new model"): a collate_multimodal_metadata patchgen helper + a get_metadata_collate_func override, the per-modality vit_metadata sub-dict threaded through Model.forward → ViT.forward (with a runtime fallback), and the model added to _MM_METADATA_WIRED_CASES in the sync gate test.

Phase 5: Test and Document

1. Create toy config: Add tests/toy_config/<model_name>_toy/config.json with minimal parameters for fast testing.

2. Unit tests: add cases to the existing enumerated tables rather than new files — tests/models/test_model_registry.py and tests/models/test_models_patch.py (TEST_CASES) already cover loading via veomni.models.auto, forward output shape, and patch application. See .agents/knowledge/testing.md for the full landing-spot table and for why a new file outside tests/ops/ / tests/data/ will not run in CI unless it is wired into the unit-test workflows.

3. E2e tests (if feasible): add a pytest.param to tests/e2e/test_e2e_parallel.py using the toy config, rather than a new e2e file.

4. Run make quality and pytest tests/models/.

5. Update documentation:

   • Add usage example to docs/ (training command, config reference).
   • Update .agents/knowledge/architecture.md if the model adds a new module or trainer path.
   • Update supported models table in project README.md if applicable.

Common Pitfalls

• Model registry: Registration must happen at import time in __init__.py. If the model's AutoConfig type is not registered, build_foundation_model() will fail.
• Tokenizer compatibility: Some models require specific tokenizer versions or custom chat templates — verify in veomni/data/chat_template.py.
• Skipping the handoff: the modeling pitfalls — never editing generated/, MoE expert layout, name_map reuse, Omni subtree exclusion — are in /veomni-patchgen-model, not here. This file deliberately does not restate them, so a summary read of Phase 2 is not enough to write a config.