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Looping a transformer reuses weights without adding parameters, but gains saturate, reverse or go unstable, and loop-specific adapters cost only 1.1 to 4.3 percent more parameters

AspireAI community · arXiv
Looping reuses a transformer's weights by repeatedly applying the same block, making a model deeper without making it larger. The paper studies the trade-off jointly across dense decoder-only models trained from scratch, spanning up to 1B parameters, 155B training tokens, 1.07 x 10 to the 21 training FLOPs and 32 loops. Looping the full transformer gave the strongest quality at a fixed parameter budget, while looping a middle block of layers gave a better return when training FLOPs were constrained. Adding loops is not uniformly beneficial: gains eventually saturate, reverse, or become unstable, which is what motivates small loop-specific low-rank adapters and a gating mechanism adding at most 0.0142 percent of non-embedding parameters. Loop-specific specialisation is parameter-efficient rather than compute-efficient, since the doubled-depth reference reached lower bits-per-byte at comparable training FLOPs, and looped transformers also pay a decoding slowdown proportional to the number of loops.
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