Mckay Wrigley posits that we have reached a pivotal moment in AI development, distinguishing the specific leap represented by the latest model generation. GPT-4 was the unlock for chat, Sonnet 3.5 was the unlock for code, and now Opus 4.5 is the unlock for agents.
This shift allows for autonomous operations over extended periods, enabling the AI to execute tasks with a level of reliability previously unattained. Thanks to Opus 4.5, agents can now work reliably on increasingly longer time horizons and get real-world work done on your behalf.
Insights
The true potential of this era is realized not just by the model itself, but through the combination of the model and its infrastructure. 2025 has been touted as the year of agents, and Opus 4.5 + Claude Agent SDK is the pairing that makes that phrase true.
This emphasizes the critical role of the environment in which the model operates, suggesting that the tooling around the AI is as important as the intelligence itself. The agent version of this is 'people who are serious about models should make their own harness'.
Consequently, users must adapt their interaction style to treat the AI as a capable partner rather than a simple tool. The best mental model for Opus 4.5 is to think of it as a coworker. A true collaborator that you can trust to get things done.
Practices
For developers, the integration of Opus 4.5 with specialized coding tools creates a powerful environment that feels almost supernatural. Claude Code + Opus 4.5 is the best AI coding tool in the world. ... It's indistinguishable from magic.
Utilizing specific features like "plan mode" can significantly enhance outcomes by structuring the AI's approach to complex problems. The new plan mode is absolutely incredible. ... It drives significantly better performance.
Additionally, guiding the model with high-level logic remains a highly effective strategy, leveraging the model's ability to interpret intent. Sometimes writing in pseudocode in the actual codebase can be unbelievably helpful. Opus 4.5 is astonishingly good at inferring what you mean when you write in pseudocode and building it out.