feat: add Mistral Small 4 (#3502)

* feat: add mistral small 4

* fix: update mistral common

* fix: deepcopy when passing in tokenizer

* feat: add doc on reasoning and thinking section

* fix: don't use custom tokenizer and quantize experts

* chore: update docs and configs

* chore: update doc to follow official name

* feat: update cce to include mistral4

* chore: move

* fix: naming

* fix: test mock breaking get_text_config check

* fix: enable CCE and add expert block targetting to configs

* chore: docs

* fix: use act checkpointing

* chore: doc

* chore: docs

* chore: docs

README.md

@@ -30,7 +30,7 @@
 ## 🎉 Latest Updates
 
 - 2026/03:
-  - New model support has been added in Axolotl for [Qwen3.5, Qwen3.5 MoE](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/qwen3.5), [GLM-4.7-Flash](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/glm47-flash), [GLM-4.6V](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/glm46v), and [GLM-4.5-Air](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/glm45).
+  - New model support has been added in Axolotl for [[Qwen3.5, Qwen3.5 MoE](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/qwen3.5), [GLM-4.7-Flash](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/glm47-flash), [GLM-4.6V](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/glm46v), and [GLM-4.5-Air](https://github.com/axolotl-ai-cloud/axolotl/tree/main/examples/glm45).
   - [MoE expert quantization](https://docs.axolotl.ai/docs/expert_quantization.html) support (via `quantize_moe_experts: true`) greatly reduces VRAM when training MoE models (FSDP2 compat).
 - 2026/02:
   - [ScatterMoE LoRA](https://github.com/axolotl-ai-cloud/axolotl/pull/3410) support. LoRA fine-tuning directly on MoE expert weights using custom Triton kernels.

docs/multimodal.qmd

@@ -13,6 +13,7 @@ format:
 - [Pixtral](#sec-pixtral)
 - [Llava-1.5](#sec-llava-15)
 - [Mistral-Small-3.1](#sec-mistral-small-31)
+- [Mistral-Small-4](#sec-mistral-small-4)
 - [Magistral-Small-2509](#sec-magistral-small-2509)
 - [Voxtral](#sec-voxtral)
 - [Gemma-3](#sec-gemma-3)
@@ -108,6 +109,12 @@ Please make sure to install vision lib via `pip install 'mistral-common[opencv]=
 base_model: mistralai/Mistral-Small-3.1-24B-Instruct-2503
 ```
 
+### Mistral-Small-4 {#sec-mistral-small-4}
+
+```yaml
+base_model: mistralai/Mistral-Small-4-119B-2603
+```
+
 ### Magistral-Small-2509 {#sec-magistral-small-2509}
 
 ::: {.callout-tip}

examples/colab-notebooks/colab-axolotl-example.ipynb

@@ -40,7 +40,7 @@
     "%%capture\n",
     "# This step can take ~5-10 minutes to install dependencies\n",
     "!pip install --no-build-isolation axolotl[flash-attn]>=0.9.1\n",
-    "!pip install \"cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@e8ad129\""
+    "!pip install \"cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@fa9a7fe\""
    ]
   },
   {

examples/mistral4/README.md

@@ -0,0 +1,85 @@
+# Finetune Mistral Small 4 with Axolotl
+
+Mistral Small 4 is a 119B parameter (6.5B active) multimodal MoE model from MistralAI that unifies instruct, reasoning, and coding capabilities into a single model. It is available on HuggingFace at [Mistral-Small-4-119B-2603](https://huggingface.co/mistralai/Mistral-Small-4-119B-2603).
+
+Thanks to the team at MistralAI for giving us early access to prepare for this release.
+
+## Getting started
+
+Note: Training this model requires weights in BF16 which we will link to later.
+Users interested in training can convert / descale the existing FP8 weights.
+
+1. Install Axolotl following the [installation guide](https://docs.axolotl.ai/docs/installation.html).
+
+2. Install [Cut Cross Entropy](https://docs.axolotl.ai/docs/custom_integrations.html#cut-cross-entropy) to reduce training VRAM usage
+
+3. Install transformers from main
+
+  ```bash
+  pip install git+https://github.com/huggingface/transformers.git
+  ```
+
+4. Run one of the example configs:
+
+  ```bash
+  # text-only
+  axolotl train examples/mistral4/qlora-text.yml  # no experts ~69 GiB, experts ~93 GiB
+  axolotl train examples/mistral4/fft-text.yml
+
+  # text + vision
+  # run: wget https://huggingface.co/datasets/Nanobit/text-vision-2k-test/resolve/main/African_elephant.jpg
+  axolotl train examples/mistral4/qlora-vision.yml  # no experts ~68 GiB
+  axolotl train examples/mistral4/fft-vision.yml
+  ```
+
+Note: FFT configs provided as reference. Please adjust hyperparameters as needed.
+
+## Reasoning Effort
+
+The chat template supports a `reasoning_effort` variable to control the model's reasoning depth:
+
+- `"none"` — instruct mode (default)
+- `"high"` — reasoning mode with explicit thinking steps
+
+Pass it via `chat_template_kwargs` under your dataset config:
+
+```yaml
+datasets:
+  - path: your/dataset
+    type: chat_template
+    chat_template_kwargs:
+      reasoning_effort: high
+```
+
+## Thinking Support
+
+The chat template supports a `thinking` content type in assistant messages for training on reasoning traces (rendered as `[THINK]...[/THINK]` blocks).
+
+To use thinking datasets, add the `thinking` mapping via `message_property_mappings`:
+
+```yaml
+datasets:
+  - path: your/thinking-dataset
+    type: chat_template
+    message_property_mappings:
+      role: role
+      content: content
+      thinking: thinking
+    chat_template_kwargs:
+      reasoning_effort: high
+```
+
+See the [Magistral thinking guide](../magistral/think/README.md) for dataset format details.
+
+## Tips
+
+- Read more on how to load your own dataset at [docs](https://docs.axolotl.ai/docs/dataset_loading.html).
+- The text dataset format follows the OpenAI Messages format as seen [here](https://docs.axolotl.ai/docs/dataset-formats/conversation.html#chat_template).
+- The vision model requires multi-modal dataset format as documented [here](https://docs.axolotl.ai/docs/multimodal.html#dataset-format).
+
+## Related Resources
+
+- [MistralAI Mistral Small 4 Blog](https://mistral.ai/news/mistral-small-4)
+- [Axolotl Docs](https://docs.axolotl.ai)
+- [Axolotl GitHub](https://github.com/axolotl-ai-cloud/axolotl)
+- [Axolotl Discord](https://discord.gg/7m9sfhzaf3)

examples/mistral4/fft-text.yml

@@ -0,0 +1,58 @@
+base_model: mistralai/Mistral-Small-4-119B-2603
+
+plugins:
+  - axolotl.integrations.cut_cross_entropy.CutCrossEntropyPlugin
+  - axolotl.integrations.kernels.KernelsPlugin
+use_kernels: true
+use_sonicmoe: true
+
+# only train language model layers, freeze vision tower
+unfrozen_parameters:
+  - model.language_model.*
+  - lm_head
+  - embed_tokens
+
+datasets:
+  - path: fozziethebeat/alpaca_messages_2k_test
+    type: chat_template
+
+dataset_prepared_path: last_run_prepared
+val_set_size: 0.01
+output_dir: ./outputs/out
+
+sequence_len: 2048
+sample_packing: true
+
+wandb_project:
+wandb_entity:
+wandb_watch:
+wandb_name:
+wandb_log_model:
+
+gradient_accumulation_steps: 1
+micro_batch_size: 1
+num_epochs: 1
+optimizer: adamw_bnb_8bit
+lr_scheduler: cosine
+learning_rate: 2e-5
+
+bf16: true
+tf32: true
+
+logging_steps: 1
+flash_attention: true
+
+warmup_ratio: 0.1
+evals_per_epoch: 1
+saves_per_epoch: 1
+weight_decay: 0.0
+
+fsdp_version: 2
+fsdp_config:
+  offload_params: false
+  cpu_ram_efficient_loading: false
+  state_dict_type: FULL_STATE_DICT
+  auto_wrap_policy: TRANSFORMER_BASED_WRAP
+  transformer_layer_cls_to_wrap: Mistral4DecoderLayer
+  reshard_after_forward: true
+  activation_checkpointing: true

examples/mistral4/fft-vision.yml

@@ -0,0 +1,57 @@
+base_model: mistralai/Mistral-Small-4-119B-2603
+processor_type: AutoProcessor
+
+plugins:
+  - axolotl.integrations.cut_cross_entropy.CutCrossEntropyPlugin
+  - axolotl.integrations.kernels.KernelsPlugin
+use_kernels: true
+use_sonicmoe: true
+
+# vision requirements
+skip_prepare_dataset: true
+remove_unused_columns: false
+sample_packing: false
+
+datasets:
+  - path: Nanobit/text-vision-2k-test
+    type: chat_template
+
+dataset_prepared_path: last_run_prepared
+val_set_size: 0.01
+output_dir: ./outputs/out
+
+sequence_len: 2048
+
+wandb_project:
+wandb_entity:
+wandb_watch:
+wandb_name:
+wandb_log_model:
+
+gradient_accumulation_steps: 1
+micro_batch_size: 1
+num_epochs: 1
+optimizer: adamw_bnb_8bit
+lr_scheduler: cosine
+learning_rate: 2e-5
+
+bf16: true
+tf32: true
+
+logging_steps: 1
+flash_attention: true
+
+warmup_ratio: 0.1
+evals_per_epoch: 1
+saves_per_epoch: 1
+weight_decay: 0.0
+
+fsdp_version: 2
+fsdp_config:
+  offload_params: false
+  cpu_ram_efficient_loading: false
+  state_dict_type: FULL_STATE_DICT
+  auto_wrap_policy: TRANSFORMER_BASED_WRAP
+  transformer_layer_cls_to_wrap: Mistral4DecoderLayer
+  reshard_after_forward: true
+  activation_checkpointing: true

examples/mistral4/qlora-text.yml

@@ -0,0 +1,58 @@
+base_model: mistralai/Mistral-Small-4-119B-2603
+
+plugins:
+  - axolotl.integrations.cut_cross_entropy.CutCrossEntropyPlugin
+
+load_in_4bit: true
+quantize_moe_experts: true
+
+datasets:
+  - path: fozziethebeat/alpaca_messages_2k_test
+    type: chat_template
+
+dataset_prepared_path: last_run_prepared
+val_set_size: 0.01
+output_dir: ./outputs/out
+
+adapter: qlora
+
+sequence_len: 2048
+sample_packing: true
+
+lora_r: 32
+lora_alpha: 16
+lora_dropout: 0.05
+lora_target_modules: 'model.language_model.layers.[\d]+.(mlp|cross_attn|self_attn).(up|down|gate|q|k|v|o)_proj'
+
+# uncomment to train on expert layers
+# lora_target_parameters:
+#   - mlp.experts.gate_up_proj
+#   - mlp.experts.down_proj
+# lora_mlp_kernel: false
+# lora_qkv_kernel: false
+# lora_o_kernel: false
+
+wandb_project:
+wandb_entity:
+wandb_watch:
+wandb_name:
+wandb_log_model:
+
+gradient_accumulation_steps: 1
+micro_batch_size: 1
+num_epochs: 1
+optimizer: adamw_bnb_8bit
+lr_scheduler: cosine
+learning_rate: 0.0002
+
+bf16: true
+tf32: true
+
+gradient_checkpointing: true
+logging_steps: 1
+flash_attention: true
+
+warmup_ratio: 0.1
+evals_per_epoch: 1
+saves_per_epoch: 1
+weight_decay: 0.0

examples/mistral4/qlora-vision.yml

@@ -0,0 +1,63 @@
+base_model: mistralai/Mistral-Small-4-119B-2603
+processor_type: AutoProcessor
+
+plugins:
+  - axolotl.integrations.cut_cross_entropy.CutCrossEntropyPlugin
+
+load_in_4bit: true
+quantize_moe_experts: true
+
+# vision chat template requirements
+skip_prepare_dataset: true
+remove_unused_columns: false
+sample_packing: false
+
+datasets:
+  - path: Nanobit/text-vision-2k-test
+    type: chat_template
+
+dataset_prepared_path: last_run_prepared
+val_set_size: 0.01
+output_dir: ./outputs/out
+
+adapter: qlora
+
+sequence_len: 2048
+
+lora_r: 32
+lora_alpha: 16
+lora_dropout: 0.05
+lora_target_modules: 'model.language_model.layers.[\d]+.(mlp|cross_attn|self_attn).(up|down|gate|q|k|v|o)_proj'
+
+# uncomment to train on expert layers
+# lora_target_parameters:
+#   - mlp.experts.gate_up_proj
+#   - mlp.experts.down_proj
+# lora_mlp_kernel: false
+# lora_qkv_kernel: false
+# lora_o_kernel: false
+
+wandb_project:
+wandb_entity:
+wandb_watch:
+wandb_name:
+wandb_log_model:
+
+gradient_accumulation_steps: 1
+micro_batch_size: 1
+num_epochs: 1
+optimizer: adamw_bnb_8bit
+lr_scheduler: cosine
+learning_rate: 0.0002
+
+bf16: true
+tf32: true
+
+gradient_checkpointing: true
+logging_steps: 1
+flash_attention: true
+
+warmup_ratio: 0.1
+evals_per_epoch: 1
+saves_per_epoch: 1
+weight_decay: 0.0

requirements.txt

@@ -75,4 +75,4 @@ axolotl-contribs-mit==0.0.6
 # telemetry
 posthog==6.7.11
 
-mistral-common==1.8.8
+mistral-common==1.10.0

scripts/cutcrossentropy_install.py

@@ -29,5 +29,5 @@ UV_PREFIX = "uv " if USE_UV else ""
 
 print(
     UNINSTALL_PREFIX
-    + f'{UV_PREFIX}pip install "cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@e8ad129"'
+    + f'{UV_PREFIX}pip install "cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@fa9a7fe"'
 )

src/axolotl/common/architectures.py

@@ -16,6 +16,7 @@ MOE_ARCH_BLOCK = {
     "qwen3_vl_moe": "Qwen3VLMoeTextSparseMoeBlock",
     "deepseek_v2": "DeepseekV2MoE",
     "deepseek_v3": "DeepseekV3MoE",
+    "mistral4": "Mistral4MoE",
     "gpt_oss": "GptOssDecoderLayer",
     "lfm2_moe": "Lfm2MoeSparseMoeBlock",
     "afmoe": "AfmoeMoE",

src/axolotl/integrations/cut_cross_entropy/README.md

@@ -19,7 +19,7 @@ python scripts/cutcrossentropy_install.py | sh
 
 - If you are installing from pip
 ```bash
-pip3 uninstall -y cut-cross-entropy && pip3 install "cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@e8ad129"
+pip3 uninstall -y cut-cross-entropy && pip3 install "cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@fa9a7fe"
 ```
 
 ## Usage
@@ -73,8 +73,10 @@ plugins:
 - ministral3
 - mistral
 - mistral3
+- mistral4
 - mixtral
 - mllama
+- nemotron_h
 - olmo
 - olmo2
 - olmo3

src/axolotl/integrations/cut_cross_entropy/__init__.py

@@ -35,7 +35,7 @@ LOG = get_logger(__name__)
 
 _CCE_INSTALL_MESSAGE = (
     "Please install Axolotl's fork of cut_cross_entropy with transformers support using "
-    '`pip install "cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@e8ad129"`'
+    '`pip install "cut-cross-entropy[transformers] @ git+https://github.com/axolotl-ai-cloud/ml-cross-entropy.git@fa9a7fe"`'
 )
 
 

src/axolotl/integrations/kernels/constants.py

@@ -25,6 +25,8 @@ SPARSE_MOE_BLOCK = {
     "olmoe": "OlmoeSparseMoeBlock",
     "mixtral": "MixtralSparseMoeBlock",
     "minimax": "MiniMaxSparseMoeBlock",
+    # softmax -> topk routing (with group-based expert selection)
+    "mistral4": "Mistral4MoE",
     # sigmoid -> topk routing (with group-based expert selection)
     "glm_moe_dsa": "GlmMoeDsaMoE",
     "deepseek_v3": "DeepseekV3MoE",

src/axolotl/integrations/kernels/plugin.py

@@ -61,9 +61,11 @@ class KernelsPlugin(BasePlugin):
         return "axolotl.integrations.kernels.KernelsArgs"
 
     def pre_model_load(self, cfg):
+        moe_model_type = cfg.model_config_type_text or cfg.model_config_type
+
         if cfg.use_scattermoe:
             self._register_kernels()
-            self._kernelize_model(cfg.model_config_type)
+            self._kernelize_model(moe_model_type)
         elif cfg.use_sonicmoe:
             if not importlib.util.find_spec("sonicmoe"):
                 raise RuntimeError(
@@ -75,11 +77,9 @@ class KernelsPlugin(BasePlugin):
 
             from axolotl.integrations.kernels.sonicmoe import patch_sonicmoe
 
-            LOG.info(
+            LOG.info(f"Applying SonicMoE patches for model type: {moe_model_type}")
-                f"Applying SonicMoE patches for model type: {cfg.model_config_type}"
-            )
             patch_sonicmoe(
-                cfg.model_config_type,
+                moe_model_type,
                 torch_compile=bool(getattr(cfg, "torch_compile", False)),
             )
 

src/axolotl/integrations/kernels/sonicmoe/routing.py

@@ -5,6 +5,7 @@ Different MoE architectures use different routing strategies:
 - qwen3_moe / qwen2_moe / qwen3_5_moe / qwen3_vl_moe / qwen3_omni_moe: softmax -> topk (with optional renormalization)
 - gpt_oss: topk -> softmax (uses fused moe_TC_softmax_topk_layer, routing_fn=None)
 - glm_moe_dsa: sigmoid -> topk (with group-based expert selection)
+- mistral4: softmax -> group selection -> topk (with renormalization and scaling)
 
 Each model type maps to a (routing_fn, activation_type, router_attr) triple.
 When routing_fn is None, the fused moe_TC_softmax_topk_layer path is used.
@@ -45,6 +46,8 @@ def get_model_moe_config(model_type: str):
         "minimax",
     ):
         return softmax_topk_routing, ActivationType.SWIGLU, "gate"
+    elif model_type in ("mistral4",):
+        return softmax_group_topk_routing, ActivationType.SWIGLU, "gate"
     elif model_type in (
         "glm_moe_dsa",
         "deepseek_v3",
@@ -126,6 +129,62 @@ def softmax_topk_routing(
     return flat_scores, flat_token_idx, flat_expert_idx, router_logits
 
 
+def softmax_group_topk_routing(
+    hidden_states: torch.Tensor, moe_block
+) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor, torch.Tensor]:
+    """Mistral4-style routing: softmax -> group selection -> topk -> renorm -> scale."""
+    gate = moe_block.gate
+    T, H = hidden_states.shape
+    K = moe_block.top_k
+    E = getattr(moe_block, "n_routed_experts", gate.weight.shape[0])
+    n_group = getattr(moe_block, "n_group", 1)
+
+    router_logits = F.linear(hidden_states, gate.weight)  # [T, E]
+    router_probs = F.softmax(router_logits, dim=-1, dtype=torch.float32)  # [T, E]
+
+    scores_for_choice = router_probs
+
+    # Group selection: pick top groups, mask the rest
+    if n_group > 1:
+        group_scores = (
+            scores_for_choice.view(-1, n_group, E // n_group)
+            .topk(2, dim=-1)[0]
+            .sum(dim=-1)
+        )
+        group_idx = torch.topk(
+            group_scores, k=moe_block.topk_group, dim=-1, sorted=False
+        )[1]
+        group_mask = torch.zeros_like(group_scores)
+        group_mask.scatter_(1, group_idx, 1)
+        score_mask = (
+            group_mask.unsqueeze(-1).expand(-1, n_group, E // n_group).reshape(-1, E)
+        )
+        scores_for_choice = scores_for_choice.masked_fill(~score_mask.bool(), 0.0)
+
+    topk_indices = torch.topk(scores_for_choice, k=K, dim=-1, sorted=False)[1]
+    topk_weights = router_probs.gather(1, topk_indices)
+
+    # Renormalization + scaling
+    norm_topk_prob = getattr(moe_block, "norm_topk_prob", True)
+    if norm_topk_prob:
+        topk_weights = topk_weights / (topk_weights.sum(dim=-1, keepdim=True) + 1e-20)
+    routed_scaling_factor = getattr(moe_block, "routed_scaling_factor", 1.0)
+    topk_weights = topk_weights * routed_scaling_factor
+
+    # Flatten for moe_general_routing_inputs
+    token_indices = (
+        torch.arange(T, device=hidden_states.device, dtype=torch.int32)
+        .unsqueeze(1)
+        .expand(T, K)
+    )
+
+    flat_scores = topk_weights.to(torch.float32).reshape(-1)  # [T*K]
+    flat_token_idx = token_indices.reshape(-1)  # [T*K]
+    flat_expert_idx = topk_indices.to(torch.int32).reshape(-1)  # [T*K]
+
+    return flat_scores, flat_token_idx, flat_expert_idx, router_logits
+
+
 def sigmoid_topk_routing(
     hidden_states: torch.Tensor, moe_block
 ) -> tuple[torch.Tensor, torch.Tensor, torch.Tensor, torch.Tensor]:

src/axolotl/loaders/model.py

@@ -829,8 +829,9 @@ class ModelLoader:
     def _set_z3_leaf_modules(self):
         from deepspeed.utils import set_z3_leaf_modules
 
-        if self.cfg.model_config_type in MOE_ARCH_BLOCK:
+        moe_type = self.cfg.model_config_type_text or self.cfg.model_config_type
-            moe_blocks = MOE_ARCH_BLOCK[self.cfg.model_config_type]
+        if moe_type in MOE_ARCH_BLOCK:
+            moe_blocks = MOE_ARCH_BLOCK[moe_type]
             moe_blocks = [moe_blocks] if isinstance(moe_blocks, str) else moe_blocks
             set_z3_leaf_modules(
                 self.model,

src/axolotl/loaders/processor.py

@@ -55,12 +55,12 @@ def load_processor(cfg: DictDefault, tokenizer: PreTrainedTokenizerBase):
         )
 
     processor_kwargs["trust_remote_code"] = cfg.trust_remote_code or False
-    processor_kwargs["tokenizer"] = tokenizer
 
     processor = processor_cls.from_pretrained(
         cfg.processor_config,
         **processor_kwargs,
     )
+    processor.tokenizer = tokenizer
 
     # Attempt to load image size from processor if available
     if (

src/axolotl/monkeypatch/multipack.py

@@ -57,6 +57,7 @@ SUPPORTED_MULTIPACK_MODEL_TYPES = [
     "olmo3",
     "ministral",
     "ministral3",
+    "mistral4",
     "afmoe",
 ]
 

src/axolotl/utils/config/__init__.py

@@ -195,6 +195,15 @@ def normalize_config(cfg):
 
     cfg.model_config_type = model_config.model_type
 
+    # Resolve inner text backbone type for VLM wrappers (e.g. mistral3 -> mistral4)
+    if callable(getattr(model_config, "get_text_config", None)):
+        text_config = model_config.get_text_config()
+        if (
+            hasattr(text_config, "model_type")
+            and text_config.model_type != model_config.model_type
+        ):
+            cfg.model_config_type_text = text_config.model_type
+
     # figure out if the model is llama
     cfg.is_llama_derived_model = (
         (