LoopCoder-v2: Only Loop Once for Efficient Test-Time Computation Scaling

Big claim in this paper, pushes against the common idea that more test-time compute should keep helping. Claims a code model gets much better when it rethinks once (i.e. by looping once) inside itself, but worse when it keeps rethinking. The first loop builds context, the second loop refines it, and later loops mostly disturb it. The paper studies a faster design called Parallel Loop Transformer, where loops can run almost in parallel and share memory, so the authors can ask a cleaner question about how many loops are actually useful. They trained 7B code models with 1, 2, 3, and 4 loops on 18T tokens, then tuned and tested them on code writing, code reasoning, software engineering, and tool-use tasks. The main result is that 2 loops worked best, raising SWE-bench Verified from 43.0 to 64.4, while 3 and 4 loops often got worse. Their internal checks suggest loop 2 does the real useful refinement, because it changes the model’s hidden states, attention patterns, and predictions in meaningful ways. After loop 2, the extra loops mostly add weaker, more repetitive changes, while a built-in position shift keeps adding the same kind of mismatch cost. Overall, the paper gives a simple lesson for efficient test-time compute: adding 1 hidden loop can help a lot, but adding more is not automatically better. ---- Link – arxiv. org/abs/2606.18023 Title: "LoopCoder-v2: Only Loop Once for Efficient Test-Time Computation Scaling"