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[Model Request] Qwen3.5 support — Gated DeltaNet + MoE architecture #778

Description

@MimiTechAi

Model Request: Qwen3.5 family

Qwen has released the Qwen3.5 model family with state-of-the-art performance that surpasses GPT-5-mini and Qwen3-235B on many benchmarks.

Available Models

Model Total Params Active Params Architecture
Qwen3.5-35B-A3B 35B 3B MoE (256 experts, 8+1 active)
Qwen3.5-27B 27B 27B Dense hybrid
Qwen3.5-122B-A10B 122B 10B MoE

Why it matters for WebLLM

Qwen3.5-35B-A3B with only 3B active parameters would be ideal for browser-based inference. Performance exceeds Qwen3-235B-A22B on agent tasks, coding (SWE-bench 69.2%), and multilingual benchmarks while requiring minimal compute per token.

New Architecture (requires TVM compiler support)

Qwen3.5 introduces a hybrid architecture different from standard transformers:

  1. Gated DeltaNet (linear attention) — 75% of layers

    • linear_conv_kernel_dim: 4, separate Q/K heads (16) and V heads (32), head_dim: 128
    • More memory-efficient than standard KV-cache
  2. Gated Full Attention — 25% of layers

    • GQA with num_attention_heads: 16, num_key_value_heads: 2, head_dim: 256
    • Partial rotary factor 0.25, interleaved mRoPE
  3. Sparse MoE: 256 experts, 8 routed + 1 shared, moe_intermediate_size: 512

  4. Multi-Token Prediction (MTP): mtp_num_hidden_layers: 1

  5. Native multimodal (vision encoder built-in)

Config

  • Architectures: Qwen3_5MoeForConditionalGeneration / Qwen3_5ForConditionalGeneration
  • Model type: qwen3_5_moe / qwen3_5
  • Layer pattern: [linear_attention × 3, full_attention × 1] repeating
  • HuggingFace: https://huggingface.co/Qwen/Qwen3.5-35B-A3B

Would love to see this in WebLLM — the 3B active MoE variant would be a game-changer for in-browser AI agents. Thank you for the amazing work! 🙏

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