Posts tagged with "Claude Opus 4.8"

Anthropic launched Claude Sonnet 5 on 30 June 2026 at an introductory 2/10 dollars per million tokens, posting 63.2% on SWE-bench Pro and near-Opus agentic performance at 40-60% of the cost per task. We run the cost math against Opus 4.8 and GPT-5.5, set out a routing framework for when the cheap model wins, and draw the continuity lesson from the eighteen-day Fable and Mythos export-control pause.

Claude Opus 4.8 arrives at unchanged pricing with an effort control on all plans, a fast mode at a third of the previous fast-inference cost, and a Messages API change that lets system entries sit inside the messages array so mid-task instruction updates no longer invalidate the prompt cache. Worked token math shows cache hit rate remains the biggest cost lever, and a four-question framework matches effort, speed and fan-out to each workload.