Data and Environment Curation for Post-Training LLMs — Mahesh Sathiamoorthy, Bespoke Labs
Jul 31, 2026 · 19:12
Mahesh Sathiamoorthy, CEO of Bespoke Labs, argues that data and RL environments, not algorithms, are the bottleneck in post-training LLMs, and shares open-source work including OpenThoughts and Curator. He details the OpenThoughts curation recipe, built with Stanford, Berkeley, and UW, whose counterintuitive lessons include that sampling multiple answers per question works well, stronger teachers are not always better, and synthetic rewriting failed for agent tasks. He notes that for agents, SFT still contributes most of the gains, with RL only adding the last few percentages. A concrete production case: Credit Karma needed compliant credit card recommendations, and tagging fine-tuning data lifted compliance metrics while improving latency and throughput. He closes with the full stack needed to build RL environments and post-train agents.
