ResearchResearch paperTraining & Scaling · Large Language Models · Efficiency & Inference1 source · Oct 15, 2026

FIRM: Fisher-Informed Retention Merging for Federated LLM Unlearning

We propose FIRM (Fisher-Informed Retention Merging), a single-round framework for stable and retention-aware server-side aggregation.

Key points

  • Federated LLM unlearning addresses targeted knowledge removal when forget and retain data remain distributed across private clients and are inaccessible to the server.
  • The resulting locally trained adapters encode conflicting objectives, making their aggregation fundamentally different from conventional federated optimization.
  • FIRM uses client-local Fisher statistics as a unified sensitivity signal to construct a Fisher-normalized base merge and impose explicit control over retain-sensitive parameters.
  • Experiments across WMDP, TOFU, and MUSE-HP using Zephyr-7B and Llama-3-8B show utility gains at comparable forgetting on WMDP and MUSE-HP, with metric-dependent trade-offs on TOFU.

Sources (1)

  • [1]FIRM: Fisher-Informed Retention Merging for Federated LLM Unlearning
    arXiv (AI, ML, NLP, CV, robotics, multi-agent) · Oct 15, 11:39 AM
    We propose FIRM (Fisher-Informed Retention Merging), a single-round framework for stable and retention-aware server-side aggregation.
    Federated LLM unlearning addresses targeted knowledge removal when forget and retain data remain distributed across private clients and are inaccessible to the server.

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