There is no established standard yet, but a clear frontrunner has emerged. The most significant proposal is Issue #136 on the agentsmd/agents.md repository (18k+ stars), filed January 8, 2026, which proposes a universal AGENT=<name> environment variable — directly modeled on the CI=true convention that unified CI/CD detection years ago. Three coding agents already ship with this convention (Goose, Amp, Bun), two detection libraries exist to paper over the fragmentation (@vercel/detect-agent and unjs/std-env), and a parallel naming camp champions AI_AGENT=<name> instead. The ecosystem is in the "organic adoption" phase, with real-world friction driving urgency.
The AGENTS.md repository — already the de facto standard for giving coding agents project-specific instructions — hosts the most authoritative proposal for e