GPT-4.1

[State of Post-Training] From GPT-4.1 to 5.1: RLVR, Agent & Token Efficiency — Josh McGrath, OpenAI

Dec 31, 2025 · 27:34

Josh McGrath, an OpenAI post-training researcher, states that real post-training innovation lies in data quality and signal trust, not optimization methods, with RLVR and token efficiency central. He moved from pre-training (3% compute gains) to post-training (40% behavior change), describes the infrastructure chaos of RL runs, and cites GRPO from DeepSeek Math as underappreciated for providing verifiable reward signals. GPT-5 to GPT-5.1 bumped evals while slashing tokens, emphasizing token efficiency over wall-clock time. The shopping model features interruptibility and chain-of-thought transparency, and personality toggles (Anton vs Clippy) are a key differentiator. For long context, he argues agents with graph walks may be more important than 10M-token windows. He concludes that the education system fails to produce people skilled in both distributed systems and ML research, a critical combination as bottlenecks shift.

Long Live Context Engineering - with Jeff Huber of Chroma

Aug 19, 2025 · 57:01

Jeff Huber, founder and CEO of Chroma, joins Shawn Wang and Alessio to argue that context engineering—not RAG—is the real job of AI builders, and that Chroma's modern retrieval engine is built for this new paradigm. Huber explains context rot, a phenomenon where LLMs lose attention and reasoning ability as context windows grow, motivating precise retrieval over huge context windows. Chroma Cloud is a zero-config, usage-based serverless vector database with separation of storage and compute, now powering 5M monthly downloads and 21k GitHub stars. He shares techniques like chunk rewriting and generative benchmarking for evaluating retrieval, and predicts LLMs will increasingly serve as re-rankers. The episode also covers memory as a benefit of context engineering, offline compaction for self-improving AI systems, and Huber's philosophy of building with long-term purpose, hiring engineers who care about Rust, TLA+, and deterministic simulation testing.

ChatGPT Codex: The Missing Manual

May 16, 2025 · 53:32

Josh Ma and Alexander Embiricos from OpenAI introduce ChatGPT Codex, a cloud-hosted autonomous software engineer that runs in its own sandbox, arguing it delivers value through single-shot, long-horizon task completion. They explain that Codex evolved from internal experiments (codenamed WHAM) and now offers a 60-tasks-per-hour rate limit with a one-hour hard cutoff, emphasizing it is not meant for interactive use but for delegation—users fire off tasks and go about their day. Best practices include using agents.md, installing linters and formatters, keeping code modular, and having good architecture. The team intentionally kept it a research preview to gather feedback on environment customization and pricing, with plans to integrate seamless transitions between cloud and CLI.