Opus 5.5 is the best Opus since 4.5

Opus 4.5 was the moment Claude Code started working the way it was meant to. I had paid for Claude Code since May 2025 without being convinced; over the 2025 Christmas break, with Opus 4.5, it carried whole projects, and I built Zentinel with it. I wrote that up in How I Work These Days and What Sixteen AI Agents Taught Me About Management, and it is the opening of my Basel talk.

Opus 5.5 is the first release since then that felt like the same kind of step rather than an increment.

• It holds the thread. Long sessions that span a theme, a site, CI, and several data files stay coherent. The search across this site, the reading log, and the agent-readable files behind them were built in sessions with it.
• Speed changes how I work with it. Fast enough that I stay in the loop instead of switching away while it runs. Fast mode exists for when that matters more than the bill.
• The cost moved the right way. A cheaper rate card than 4.5, and Anthropic puts it at about 40 per cent cheaper to run than Opus 5 on typical work. The rate card is half the story; fewer wasted turns is the other half, the same argument I made in The Economics of Inference.
• Opus is the default again. For most of my work I no longer pick a smaller model to save money, which was the point of 4.5 too.

What I do not know yet: whether it holds up on the hardest, longest-running tasks, where the gap to a larger model would show first. A month is not a benchmark.

Sources: Introducing Claude Opus 4.5, Introducing Claude Opus 5.5, Opus 5.5 model overview.