[Bugfix][Model] Fix Devstral Small 2 HF format weight loading by thomasmaindron · Pull Request #39293 · vllm-project/vllm

thomasmaindron · 2026-04-08T10:45:20Z

Summary

Fix issues preventing Mistral3 models (e.g. Devstral Small 2) from loading in HF format (--config-format hf --load-format hf --tokenizer-mode hf):

FP8 scale name mismatch: HF checkpoints use activation_scale and weight_scale_inv but vLLM's FP8 linear layers register them as input_scale and weight_scale. Added suffix remapping in hf_to_vllm_mapper.
Register Ministral3ForCausalLM in the model registry, mapping it to the existing MistralForCausalLM implementation.
Remove redundant Pixtral-12B special case in mistral3.py — now handled globally by with_hf_config ( [Bug] Fix TypeError when hf_config.architectures is None during model loading #38849).

Fixes #38818

Test plan

Verified FP8 scale values are identical between native (qscale_weight/qscale_act) and HF (weight_scale_inv/activation_scale) formats by comparing tensors in safetensors files
Model loads successfully with vllm serve devstral-small-2 --config-format hf --load-format hf --tokenizer-mode hf
Inference works correctly on Open-WebUI

🤖 Generated with Claude Code

Co-authored-by: Claude Opus 4.6 (1M context)

github-actions · 2026-04-08T10:45:33Z

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Code Review

This pull request introduces support for the Ministral3ForCausalLM architecture, including its registration in the model registry and updates to Mistral3ForConditionalGeneration for handling FP8 quantization scales. Additionally, it improves the robustness of architecture resolution in model_loader/utils.py by safely handling null architecture attributes. Feedback was provided regarding the hardcoded architecture list in Mistral3ForConditionalGeneration, suggesting it be used as a default rather than an absolute override to preserve flexibility for custom configurations.

gemini-code-assist · 2026-04-08T10:47:58Z

@@ -437,6 +444,7 @@ def __init__(self, *, vllm_config: VllmConfig, prefix: str = "") -> None:
            self.language_model = init_vllm_registered_model(
                vllm_config=vllm_config,
                hf_config=config.text_config,
+                architectures=["Ministral3ForCausalLM"],


Hardcoding the architecture list here acts as an override, which will ignore any architectures explicitly defined in the model's text_config. It is better to provide this as a default value so that custom architectures can still be resolved if present in the configuration.

Suggested change

architectures=["Ministral3ForCausalLM"],

architectures=config.text_config.architectures or ["Ministral3ForCausalLM"],

Fix issues preventing Mistral3 models (e.g. Devstral Small 2) from loading in HF format with --config-format hf --load-format hf: 1. FP8 scale name mismatch: HF checkpoints use "activation_scale" and "weight_scale_inv" but vLLM's FP8 linear layers register them as "input_scale" and "weight_scale". Add suffix remapping in hf_to_vllm_mapper. 2. Register Ministral3ForCausalLM in the model registry, mapping it to the existing MistralForCausalLM implementation. 3. Remove now-redundant Pixtral-12B architecture special case in mistral3.py (handled globally by with_hf_config). Fixes vllm-project#38818 Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com>

thomasmaindron · 2026-04-13T12:02:31Z

@hmellor This PR is rebased on main now that #38849 is merged. The diff is just the FP8 scale remapping and Ministral3 registry entry, ready for review when you get a chance.

@juliendenize FYI this implements the remaining pieces for Devstral HF format support on top of your architecture resolution feedback.

juliendenize

Hey thanks for the contribution, I just got a question regarding some removal if you could give some context there 😄

juliendenize · 2026-04-13T16:25:44Z

-        if (
-            config.text_config.architectures is None
-            and config.text_config.model_type == "mistral"
-        ):
-            config.text_config.architectures = ["MistralForCausalLM"]


This is removed due to previous PR ?

Yes, #38849 now resolves missing architectures globally in VllmConfig.with_hf_config using MODEL_FOR_CAUSAL_LM_MAPPING_NAMES[model_type]. For Pixtral-12B, model_type=mistral maps to MistralForCausalLM, so this special case became redundant.

juliendenize

Thanks for the effort, looks good !

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com>

…roject#39293) Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: zengxian <xiangdong.zeng@intel.com>

…roject#39293) Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…roject#39293) Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Avinash Singh <avinashsingh.rcoem@gmail.com>

…roject#39293) Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com>

…roject#39293) Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: thomasmaindron <thomasmaindron@users.noreply.github.com> Co-authored-by: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: Matt Van Horn <455140+mvanhorn@users.noreply.github.com>

thomasmaindron requested review from 22quinn, DarkLight1337, patrickvonplaten and ywang96 as code owners April 8, 2026 10:45

mergify Bot added multi-modality Related to multi-modality (#4194) new-model Requests to new models bug Something isn't working labels Apr 8, 2026

gemini-code-assist Bot reviewed Apr 8, 2026

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thomasmaindron force-pushed the fix/devstral-hf-weight-loading branch from ba15061 to d27614e Compare April 8, 2026 11:05

TihoElek mentioned this pull request Apr 8, 2026

[Bug] Fix TypeError when hf_config.architectures is None during model loading #38849

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thomasmaindron force-pushed the fix/devstral-hf-weight-loading branch from d27614e to 18a611d Compare April 9, 2026 09:44

thomasmaindron requested review from ProExpertProg, WoosukKwon, hmellor, houseroad, mgoin, robertgshaw2-redhat, tlrmchlsmth, yewentao256 and youkaichao as code owners April 9, 2026 09:44

thomasmaindron force-pushed the fix/devstral-hf-weight-loading branch 2 times, most recently from 47b12cb to 3adfbce Compare April 9, 2026 11:45

mergify Bot added the mistral Related to Mistral models label Apr 10, 2026

thomasmaindron force-pushed the fix/devstral-hf-weight-loading branch from 3adfbce to fb4766f Compare April 13, 2026 11:57

thomasmaindron mentioned this pull request Apr 13, 2026

[Bugfix][Parser] Fix Mistral tool parser for HF tokenizers #39294

Merged

2 tasks

juliendenize reviewed Apr 13, 2026

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juliendenize approved these changes Apr 14, 2026

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DarkLight1337 approved these changes Apr 14, 2026

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DarkLight1337 enabled auto-merge (squash) April 14, 2026 07:54

github-actions Bot added the ready ONLY add when PR is ready to merge/full CI is needed label Apr 14, 2026

Add Ministral3ForCausalLM to test model registry

c3ffe76

Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com> Signed-off-by: thomasmaindron <thomasmaindron@users.noreply.github.com>

auto-merge was automatically disabled April 14, 2026 08:44
Head branch was pushed to by a user without write access

Merge branch 'main' into fix/devstral-hf-weight-loading

553f02f

DarkLight1337 enabled auto-merge (squash) April 14, 2026 08:53

DarkLight1337 merged commit 6f786f2 into vllm-project:main Apr 14, 2026
58 checks passed

thomasmaindron deleted the fix/devstral-hf-weight-loading branch April 24, 2026 11:21

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[Bugfix][Model] Fix Devstral Small 2 HF format weight loading#39293

[Bugfix][Model] Fix Devstral Small 2 HF format weight loading#39293
DarkLight1337 merged 3 commits into
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	architectures=["Ministral3ForCausalLM"],
	architectures=config.text_config.architectures or ["Ministral3ForCausalLM"],

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