/nemo-automodel-model-onboarding

name: nemo-automodel-model-onboarding
description: Guide for onboarding new model architectures into NeMo AutoModel, including architecture discovery, implementation patterns, registration, and validation.
when_to_use: Adding or modifying model architecture support in NeMo AutoModel, such as LLM/VLM/MoE model files, custom layers, state-dict adapters, registry entries, Hugging Face config mapping, or capability flags.
license: Apache-2.0
metadata:
  author: NVIDIA
  tags:
    - nemo-automodel
    - model-onboarding

Adding Model Support to NeMo AutoModel

Purpose

This skill guides implementation of new model architectures in NeMo AutoModel. Follow the five phases in order. <!-- NVSkills signature refresh requested after PR #2998 (2026-07-31). -->

Instructions

When answering an onboarding question, keep the response in this order:

1. Classify the architecture from `config.json`. 2. Name the exact implementation files under `components/models/<name>/`. 3. Identify registry and optional custom-config updates. 4. State the validation tests that must be added before full checkpoint use.

For conceptual onboarding questions, answer from this skill without opening the pattern files unless the user asks you to edit code. Mention pattern filenames as references, then give the direct checklist.

Use direct action verbs: classify the model, name the files, map the weights, register the class, and add tests. Do not discuss distributed strategy, launcher configuration, or general recipe authoring unless the user explicitly connects it to onboarding a new architecture.

Examples

Use these compact answer patterns for common questions:

• Dense causal LM: classify as dense only when `architectures` contains a

`ForCausalLM` class and expert fields such as `num_local_experts`, `n_routed_experts`, or `num_experts_per_tok` are absent. Create `components/models/<name>/model.py` and `__init__.py`; add `state_dict_adapter.py` only for checkpoint weight conversion and `config.py` only if needed. Register `MODEL_ARCH_MAPPING` in `_transformers/registry.py`, add example YAML, and add tiny-config unit tests plus layer-equivalence tests for rewritten layers.

• MoE state dict: identify expert fields in `config.json`, reference

`moe-patterns.md`, map router tensors separately, preserve routed-expert index order, map routed experts, shared experts, and gate/up/down projections, add adapter key-map tests and tiny-config numerical equivalence tests, and do not rely only on `from_pretrained()` or silent tensor reshapes.

• VLM onboarding: classify as VLM only when `vision_config`, `text_config`, and

a `ForConditionalGeneration` architecture are present. Reference `vlm-patterns.md` and existing VLM implementations such as `mistral4`, `kimivl`, or `kimi_k25_vl`; check text backbone, vision tower, projector, processor assumptions, text and vision checkpoint compatibility (adapter mappings when needed), registry registration, and tiny image-text tests before full checkpoints. Do not treat VLM onboarding as a pure causal-LM path or skip processor/image tests.

For MoE state-dict and VLM questions, apply the checklists in Sections 2.4 and 2.5.

Routing Boundary

Use this skill only when the user is adding or modifying model architecture support: model files, custom layers, state-dict adapters, Hugging Face config mapping, registry entries, or model capability flags.

Do not use this skill for standalone training recipe YAML questions about optimizers, datasets, schedulers, validation datasets, or trainer wiring unless they are explicitly part of onboarding a new model architecture. Those recipe questions belong to the nemo-automodel-recipe-development skill.

In-scope examples:

• "Add support for a new Hugging Face causal LM architecture."
• "Map MoE router and expert weights from a Hugging Face checkpoint."
• "Register a new model class in NeMo AutoModel."

Out-of-scope examples:

• "Write a finetuning recipe YAML with optimizer and dataset sections."
• "Choose FSDP2, DDP, tensor parallel, or context parallel settings."
• "Configure Slurm, SkyPilot, containers, mounts, or launch dispatch."

Phase 1: Discovery

Before writing code, gather information about the target model.

1.1 Fetch HuggingFace config.json

Download the model's `config.json` from the HuggingFace Hub (or use `AutoConfig.from_pretrained`). Key fields to extract:

• `architectures` -- determines the class name and registration key (e.g., `"LlamaForCausalLM"`, `"Qwen3MoeForCausalLM"`, `"Mistral3ForConditionalGeneration"`)
• `model_type` -- used for custom config registration in `_CUSTOM_CONFIG_REGISTRATIONS` if HF does not have a built-in config class
• `hidden_size`, `intermediate_size`, `num_hidden_layers`, `num_attention_heads`, `num_key_value_heads` -- sizing
• `vocab_size` -- needed for tiny test configs
• `tie_word_embeddings` -- the saved setting in each supported checkpoint; do not infer it from a bare config constructor
• `hidden_act` -- activation function (e.g., `"silu"` for SwiGLU)

1.2 Determine model type

| Type | Indicators | Pattern file | |------|-----------|-------------| | **Dense LLM** | `ForCausalLM` in architectures, no expert fields | [llm-patterns.md](./llm-patterns.md) | | **MoE LLM** | `n_routed_experts`, `num_local_experts`, `num_experts_per_tok` in config | [moe-patterns.md](./moe-patterns.md) | | **VLM** | `ForConditionalGeneration` in architectures, has `vision_config` + `text_config` | [vlm-patterns.md](./vlm-patterns.md) |

1.3 Check for existing similar architectures

Look in `components/models/` for architectures with similar attention or MLP patterns:

components/models/
  llama/           # Standard GQA + SwiGLU with separate HF-compatible projections
  qwen2/           # Same as Llama but with attention bias + QKV bias
  baichuan/        # ALiBi attention variant
  deepseek_v3/     # MLA attention + MoE (DeepSeek-style grouped experts)
  mistral4