TL;DR for engineering leaders
For deep, multi-step tool-use agents against internal systems, Claude (Sonnet 4.5 or Opus 4) plus MCP is the shorter path to production today: typed tool schemas, first-class MCP servers, and a longer context window mean fewer scaffolding decisions and less glue code. OpenAI (GPT-5 with the Responses API and Assistants) wins when the surface is a broad general-purpose assistant, multi-modal is central, or business users need the polished ChatGPT UI. Most enterprises end up running both, scoped to different jobs: pick per workflow, not per vendor.