GPT-5.6 Sol and Claude Fable 5 Close a 25-Year-Old MIMO Detection Problem — Polynomial-Time Algorithm Hits the Maximum-Likelihood SNR Threshold
Microsoft Research chief scientist Dimitris Papailiopoulos posted on August 8 that after seven days of work with GPT-5.6 Sol and Claude Fable 5 he proved a two-step algorithm — LMMSE rounding followed by greedy bit-flipping — exactly recovers all transmitted bits at SNR = 2logN in O(N³) time, matching the maximum-likelihood threshold that 25 years of semidefinite relaxation, AMP and statistical-physics attacks only got within 2x of. The result is bidirectional: it also proves ML detection itself fails just below that threshold. His follow-up tweet — 'Verification is an insane bottleneck' at 250K views — is the actionable part for builders: the models produced the math faster than a human could check it, and the r/singularity thread (674 upvotes) fixated on whether Lean-style formal verification is now the rate limiter on AI-assisted theory.
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