F500 AI exec who still ships. Author of Builder-Leader. The builds, the numbers, what broke. The Blog → https://xitter.cf/t.co/RnVFhevL0J

Washington, DC
Joined July 2026
Justin Johnson retweeted
Opus 5.5 is a really good model. It's been my daily driver the last few weeks. We had Opus 5.5 and Fable 5.1 each port HAProxy from C to Rust. Both passed nearly all of HAProxy's tests, but Opus 5.5 finished in 9.5 hours compared to Fable 5.1's 12 hours, and for 51% less cost.
Introducing Claude Opus 5.5, the first model in our new Claude 5.5 family. It performs at the level of Claude Fable 5.1 for most tasks, and costs 40% less to run than Opus 5.
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Justin Johnson retweeted
This is one of the most useful writeups I have seen on keeping an LLM judge effective in production. (bookmark it) Netflix runs judges over hundreds of thousands of show-level recommendation explanations per week, served to millions of members on mobile. They describe the judge as a lifecycle with four phases rather than an artifact that you only validate once. > Birth defines multiple evaluation criteria and builds curated benchmarks with human labels and rationales. > Training refines the judge's rubric through Reasoning-Aligned Rubric Tuning, using a meta-judge over reasoning output as the learning signal. > Deployment puts one judge in two roles, quality gating and reflective generation. > Monitoring runs continuous human-in-the-loop alignment that detects drift and triggers re-tuning behind a review gate. A five-week A/B test over tens of millions of members shifted viewing toward previously unwatched content and increased successful browse-to-play sessions against a no-explanation control, with no quality-related takedowns. Paper: arxiv.org/abs/2608.18300 Track more trending AI papers in our academy: academy.dair.ai/
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Justin Johnson retweeted
A in-depth review of AI for drug discovery "It can be concluded that we are still at a stage with an ‘absence of evidence’ (and not necessarily an 'evidence of absence') when it comes to the translation of AI into clinically relevant impact." @NatRevDrugDisc nature.com/articles/s41573-0…
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