If you mostly use chat AI and you've started tracking new tools because you don't want to fall behind, this is the part that actually changes your next move. The easy mistake is thinking stronger models make prompts and project docs less important. The reversal is rougher: Better Models: Worse Tools.
The file that gains value is not another clever prompt. It is AGENTS.md: the guide file stored inside a project folder. Once the model gets stronger, that project guide can matter more than the prompt, because it tells the tool how to behave inside the project. That is why the most valuable code file may now be AGENTS.md.
This matters even if you are not an engineer. If you only watch launch videos and feature lists, you can spend time, budget, and attention in the wrong place. The hidden cost is slower judgment. You keep chasing surface upgrades and miss the file that actually changes what the tool does when it touches a real project.
One study examined 253 Claude.md files and described them as project-level context and operating rules for agents, with the content concentrated around commands, implementation guidance, and architecture [S001]. In plain English, these files are not side notes. They are becoming part of the tool's input surface.
The signal is getting bigger, not smaller. Reporting around the Linux Foundation handoff said AGENTS.md had already been adopted by more than 60,000 projects [S002]. But there is a catch: project-level context files can also change agent behavior in bad ways. Another paper found they could reduce success rates and raise reasoning cost by more than 20% [S003]. So the goal is not 'write more docs.' The common failure mode is turning AGENTS.md into a bloated README copy.
A tool update is not worth your attention because it lists more features. It matters if it changes your next decision. If someone around you is still polishing prompts while ignoring the project guide file, share this with them.