Alternate command for 1 GPU:

sockeye-train \
    --prepared-data prepared --validation-source dev.en.bpe \
    --validation-target dev.de.bpe --output model --num-layers 6 \
    --transformer-model-size 1024 --transformer-attention-heads 16 \
    --transformer-feed-forward-num-hidden 4096 --amp --batch-type max-word \
    --batch-size 5000 --update-interval 80 --checkpoint-interval 500 \
    --max-updates 15000 --optimizer-betas 0.9:0.98 \
    --initial-learning-rate 0.06325 \
    --learning-rate-scheduler-type inv-sqrt-decay --learning-rate-warmup 4000 \
    --seed 1