# Add a new model architecture to `llama.cpp`

Adding a model requires few steps:

1. Convert the model to GGUF
2. Define the model architecture in `llama.cpp`
3. Build the GGML graph implementation
4. Optional: Add multimodal encoder implementation

After following these steps, you can open PR.

Also, it is important to check that the examples and main ggml backends (CUDA, METAL, CPU) are working with the new architecture, especially:
- [cli](/tools/cli/)
- [completion](/tools/completion/)
- [imatrix](/tools/imatrix/)
- [quantize](/tools/quantize/)
- [server](/tools/server/)

### 1. Convert the model to GGUF

This step is done in python with a `convert` script using the [gguf](https://pypi.org/project/gguf/) library.
Depending on the model architecture, you can use either [convert_hf_to_gguf.py](/convert_hf_to_gguf.py) or [examples/convert_legacy_llama.py](/examples/convert_legacy_llama.py) (for `llama/llama2` models in `.pth` format).

The convert script reads the model configuration, tokenizer, tensor names+data and converts them to GGUF metadata and tensors.

The required steps to implement for an HF model are:

1. Define the model `ModelBase.register` annotation in a new `TextModel` or `MmprojModel` subclass in the [conversion](/conversion) folder, example:

```python
@ModelBase.register("MyModelForCausalLM")
class MyModel(TextModel):
    model_arch = gguf.MODEL_ARCH.MYMODEL
```

or

```python
@ModelBase.register("MyModelForConditionalGeneration")
class MyModel(MmprojModel):
    model_arch = gguf.MODEL_ARCH.MYMODEL
```

2. Define the layout of the GGUF tensors in [constants.py](/gguf-py/gguf/constants.py)

Add an enum entry in `MODEL_ARCH`, the model human friendly name in `MODEL_ARCH_NAMES` and the GGUF tensor names in `MODEL_TENSORS`.

Example for `falcon` model:
```python
    MODEL_ARCH.FALCON: [
        MODEL_TENSOR.TOKEN_EMBD,
        MODEL_TENSOR.OUTPUT_NORM,
        MODEL_TENSOR.OUTPUT,
        MODEL_TENSOR.ATTN_NORM,
        MODEL_TENSOR.ATTN_NORM_2,
        MODEL_TENSOR.ATTN_QKV,
        MODEL_TENSOR.ATTN_OUT,
        MODEL_TENSOR.FFN_DOWN,
        MODEL_TENSOR.FFN_UP,
    ]
```

3. Map the original tensor names to the standardize equivalent in GGUF

As a general rule, before adding a new tensor name to GGUF, be sure the equivalent naming does not already exist.

Once you have found the GGUF tensor name equivalent, add it to the [tensor_mapping.py](/gguf-py/gguf/tensor_mapping.py) file.

If the tensor name is part of a repetitive layer/block, the key word `bid` substitutes it.

Example for the normalization tensor in attention layers:

```python
block_mappings_cfg: dict[MODEL_TENSOR, tuple[str, ...]] = {
        # Attention norm
        MODEL_TENSOR.ATTN_NORM: (
            "gpt_neox.layers.{bid}.input_layernorm",                # gptneox
            "transformer.h.{bid}.ln_1",                             # gpt2 gpt-j refact qwen
            "transformer.blocks.{bid}.norm_1",                      # mpt
            ...
        )
}
```

`transformer.blocks.{bid}.norm_1` will be mapped to `blk.{bid}.attn_norm` in GGUF.

Depending on the model configuration, tokenizer, code and tensors layout, you will have to override:
- `TextModel#set_gguf_parameters`
- `MmprojModel#set_gguf_parameters`
- `ModelBase#set_vocab`
- `ModelBase#modify_tensors`

NOTE: Tensor names must end with `.weight` or `.bias` suffixes, that is the convention and several tools like `quantize` expect this to proceed the weights.

### 2. Define the model architecture in `llama.cpp`

The model params and tensors layout must be defined in `llama.cpp` source files:
1. Define a new `llm_arch` enum value in `src/llama-arch.h`.
2. In `src/llama-arch.cpp`:
    - Add the architecture name to the `LLM_ARCH_NAMES` map.
    - You may also need to update `LLM_KV_NAMES`, `LLM_TENSOR_NAMES` and `LLM_TENSOR_INFOS`
3. Add any non-standard metadata loading in the `llama_model_loader` constructor in `src/llama-model-loader.cpp`.
4. If the model has a RoPE operation, add a case for the architecture in `llama_model_rope_type` function in `src/llama-model.cpp`.

NOTE: The dimensions in `ggml` are typically in the reverse order of the `pytorch` dimensions.

### 3. Build the GGML graph implementation

This is the funniest part, you have to provide the inference graph implementation of the new model architecture in `src/llama-model.cpp`:
1. Create a new struct that inherits from `llama_model_base`.
2. Implement the graph-building logic in its `build_arch_graph` method.
3. The `build_arch_graph` method should return a constructed graph (inherited from `llm_graph_context`). Have a look at existing implementations like `llama_model_llama`, `llama_model_dbrx` or `llama_model_bert`.
4. Then, in the `llama_model_mapping` function, add a case for your architecture to instantiate your new graph-building struct.

Some `ggml` backends do not support all operations. Backend implementations can be added in a separate PR.

Note: to debug the inference graph: you can use [llama-eval-callback](/examples/eval-callback/).

### 4. Optional: Add multimodal encoder implementation

If the new model supports multimodal inputs, you will need to add a new encoder definition in `libmtmd`. You can find more information about llama.cpp's multimodal support in [the docs](../multimodal.md) and in the `tools/mtmd` source directory.

1. In the conversion script, make sure you add a subclass that extends `MmprojModel` or another class that inherits from the same base class.
2. Add the encoder definition in `clip.cpp`.
3. Implement the preprocessor in `mtmd.cpp`. In most cases, you can reuse an existing preprocessor.
4. Implement the encoder GGML graph, either in a dedicated file if the model is truly different from existing ones, or by reusing an existing implementation (for example: siglip, pixtral, or qwen) and adding a model-specific projector.

Note:
- Many multimodal encoders are based on models that are already supported. Make sure to read the existing encoder definitions in `tools/mtmd/models` before adding a new one. In `libmtmd`, it is generally better to extend an existing model than to duplicate code.
- To debug the multimodal preprocessor and encoder, you can use [llama-mtmd-debug](tools/mtmd/debug/mtmd-debug.cpp).
- Adding a model-specific API or CLI is an anti-pattern in `libmtmd`. The goal of `libmtmd` is to provide an easy-to-use, model-agnostic library for multimodal pipeline.
- In most cases, `llama-mtmd-cli` should not be modified. If a model requires a specific prompt, either let the user provide it or bake it into the Jinja chat template.

## Tips and tricks

### Working with ggml_rope_ext

PyTorch implementations usually prefer explicitly calculating `freq_cis`/`sin`/`cos` components. However, in llama.cpp, most RoPE operations can be handled via `ggml_rope_ext`, which does not require a sin/cos matrix. This saves memory while allowing the GGML RoPE kernel to be fused with other ops.

However, since `ggml_rope_ext` only provides a subset of the RoPE implementations that models use, converting models from PyTorch to llama.cpp may require some creative adaptations.

For more information about `ggml_rope_ext`, please refer to the in-code documentation in `ggml.h`.

Examples:
- `libmtmd` implements 2D RoPE with `GGML_ROPE_TYPE_NORMAL` ordering by splitting the input tensor in half, applying `ggml_rope_ext` separately to each half, then joining them back together using `ggml_concat`.
- The [Kimi-K2.5](https://github.com/ggml-org/llama.cpp/pull/19170) vision encoder uses vision RoPE with interleaved frequencies. The weights must be permuted during conversion in order to reuse the `build_rope_2d()` function.
- [Gemma 4](https://github.com/ggml-org/llama.cpp/pull/21309) uses "proportional" RoPE. We employ a trick where `rope_freqs` is set to a very large value in the last dimensions to prevent those dimensions from being rotated. See the `Gemma4Model` class in `convert_hf_to_gguf.py`.
- Some models require scaling the input position. For example, `[0, 1, 2, ...]` becomes `[0, 0.5, 1, ...]`. In this case, you can provide the scaling via `freq_scale = 0.5f`.
- Some models use learned RoPE frequencies instead of relying on `powf(freq_base, -2.0 * i / n_dims)`. In this case, you can provide the learned frequencies via the `rope_freqs` tensor (corresponding to the `c` argument in `ggml_rope_ext`), then set `freq_base = 1.0f`. An important note is that `rope_freqs` in GGML is the **inverse** (`theta = pos[i] / rope_freqs`), so you may need to invert `rope_freqs` during conversion.

## GGUF specification

https://github.com/ggml-org/ggml/blob/master/docs/gguf.md

## Resources

- YaRN RoPE scaling https://github.com/ggml-org/llama.cpp/pull/2268
- support Baichuan serial models https://github.com/ggml-org/llama.cpp/pull/3009
- support attention bias https://github.com/ggml-org/llama.cpp/pull/4283
- Mixtral support https://github.com/ggml-org/llama.cpp/pull/4406
- BERT embeddings https://github.com/ggml-org/llama.cpp/pull/5423
- Grok-1 support https://github.com/ggml-org/llama.cpp/pull/6204
- Command R Plus support https://github.com/ggml-org/llama.cpp/pull/6491
- support arch DBRX https://github.com/ggml-org/llama.cpp/pull/6515
- How to convert HuggingFace model to GGUF format https://github.com/ggml-org/llama.cpp/discussions/2948
