fix(modernbert): use config hidden_activation in MLP (support silu for Granite)#211
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amgix-dev wants to merge 1 commit into
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fix(modernbert): use config hidden_activation in MLP (support silu for Granite)#211amgix-dev wants to merge 1 commit into
amgix-dev wants to merge 1 commit into
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ModernBertMLP always applied gelu_erf on the gate tensor, but some ModernBERT-based models (e.g. ibm-granite/granite-embedding-97m-multilingual-r2) set hidden_activation: "silu" in config.json. Read hidden_activation from config (default: gelu) and use the matching gated-FFN activation. Missing config field keeps existing GeGLU behavior.
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Problem
ModernBertMLPalways usedgelu_erf()on the gate branch of the gated FFN, regardless ofconfig.json.Models such as
ibm-granite/granite-embedding-97m-multilingual-r2sethidden_activation: "silu"(SwiGLU-style). Running them with GeGLU produces incorrect hidden states and poor embedding quality.Solution
hidden_activationtoConfig(#[serde(default)]for backward compatibility)"gelu"→gelu_erf()(default when field is absent)"silu"→silu()Backward compatibility
Existing ModernBERT checkpoints without
hidden_activationin config continue to usegelu, matching current behavior.Testing
Verified embedding parity against Sentence Transformers implementation:
ibm-granite/granite-embedding-97m-multilingual-r2(hidden_activation: silu): Sentence Transformer parity, cosine ≈ 1.0Alibaba-NLP/gte-modernbert-base(hidden_activation: gelu): Sentence Transformer parity, cosine ≈ 1.0