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).
NOTE: Pick the GGUF arch string (and the matching `src/models/<name>.cpp` filename, see section 3) carefully up front, following existing naming conventions. Once GGUF files are published under a given arch string, renaming it later breaks the community's existing files, so this is not something to leave for cleanup in a follow-up PR.
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.
5. Check for other places that switch/iterate over every `llm_arch` value, e.g. `src/llama-model-saver.cpp` and any mandatory-hparam lists (such as which archs require MoE metadata). Grep for `LLM_ARCH_` usages to find them. Missing one of these is a common cause of CI test failures (e.g. `test-llama-archs`) after adding a new arch.
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.
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.
### Prefer conversion-time tensor modifications over graph-time ones
If the model contains constant modifications of tensors in the graph (for example, `norm(1 + weight)`) or performs tensor permutations/chunking, perform the modifications during conversion rather than in the graph code. This keeps the inference graph simpler and avoids extra runtime ops.
Examples:
- Gemma 3 folds the `1 +` of its `norm(1 + weight)` normalization into the weights at conversion time, so the graph just does a plain RMS norm.
- Qwen3-Next applies its tensor permutation during conversion (in `modify_tensors`), so the graph can consume the already-permuted weights directly.
Exception: a plain `weight * scale` with a constant scale is usually better left to inference time rather than folded into the weight at conversion. The scale conceptually applies to the activation, not the weight, so folding it into the weight can hurt numerical stability, and it shifts the weight's value range in a way that can make quantization worse. In this case, write the scale to GGUF as its own metadata key (e.g. `%s.attention.output_scale`, `%s.attention.value_scale`, `%s.embedding_scale`) and apply it in the graph, instead of pre-multiplying the weight tensor during conversion.
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.
