As of August 2026, calling Microsoft 365 Copilot programmatically means choosing between two distinct implementations — the Work IQ Chat API (general availability, one permission, Copilot Credits billing) and the Graph beta Chat API (preview, seven required delegated scopes, flat M365 Copilot license) — and that choice shapes your authentication architecture, your enterprise admin consent conversation, and your billing model before you write a line of code. This post covers the complete request and response shape for both paths, the permission and billing models that cannot be swapped at go-live, and the five things neither implementation can do regardless of which path you choose.