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Megatron-HF Bridge Backend

AReaL currently supports two bridge backends for MegatronEngine:

  • mbridge (default)
  • megatron-bridge

Set the backend with:

actor:
  megatron:
    bridge_type: mbridge
  • Use bridge_type=megatron-bridge to enable the new path.
  • mbridge is the default choice if this argument is not present

Why this feature exists

  • mbridge is being deprecated and does not provide PEFT/LoRA support.
  • megatron-bridge supports more/ newer model architectures.
  • megatron-bridge provides built-in PEFT/LoRA implementations.

Recommendation

  • For new GPU training workflows, prefer megatron-bridge.
  • Keep mbridge for backward compatibility and environments that still depend on it.
  • Prefer mbridge when using disk-based weight broadcast as it has optimized HF load/save path.
  • If you use XCCL for weight broadcast, load/save time is less important.

Current limitation

  • Tree-attention training in MegatronEngine currently supports only mbridge.
  • The megatron-bridge backend is not supported in the tree-attention path yet.
  • megatron-bridge does support faster/optimized HF model load/save implementations.