# Delta Compression

Fireworks released ARCv3, a compressor that turns the BF16 weight updates a trainer sends to rollout machines into compact deltas. Cross-region reinforcement learning previously meant shipping full checkpoints or relying on compressors such as ARCv2; ARCv3 encodes the bit-level structure of weight changes, sending mostly mantissa bits and packing rare exponent and sign changes separately. Across 1,000 weight-update deltas from production RL workloads, ARCv3 produced an average payload of about 0.19% of the original BF16 weight size, down from 0.36% for ARCv2, with bit-for-bit reconstruction of the trainer's weights.

Fireworks released ARCv3, a compressor that turns the BF16 weight updates a trainer sends to rollout machines into compact deltas. Cross-region reinforcement learning previously meant shipping full checkpoints or relying on compressors such as ARCv2; ARCv3 encodes the bit-level structure of weight changes, sending mostly mantissa bits and packing rare exponent and sign changes separately. Across 1,000 weight-update deltas from production RL workloads, ARCv3 produced an average payload of about 0.19% of the original BF16 weight size, down from 0.36% for ARCv2, with bit-for-bit reconstruction of the trainer's weights.