MCP and SPN

Summary

The news half covers Opus 5 arriving with unusually little fanfare, which both hosts read as a sign that attention has moved to price-performance rather than raw capability, and OpenAI’s 80% price cut on Luna alongside a 20% cut on Terra — leaving a roughly 50x input-token gap between Luna and Fable. That leads into a disagreement worth hearing: Mike argues the limiting factor on agent output is usually the operator’s planning and prompting, while Matthias ranks a solid test harness above a good plan, on the grounds that an agent that cannot self-validate will only ever get so far. The demo then builds the whole service principal path end to end — app registration in Entra, client secret, workspace access, the Fabric admin portal group — and connects VS Code to a semantic model over XMLA with no user identity and no Pro licence. Matthias supplies two of the episode’s most useful warnings along the way: get the .gitignore in place before writing anything to .env, and do not add API permissions to the app registration, which silently breaks the handshake. They close on the difficulty of judging model quality independent of price, and on DAX Bench as one community attempt at it.

Key Takeaways

• ▸ Opus 5 shipped quietly, and the interesting story in the graphs is score per unit of cost rather than the score alone — the min-maxing phase of model selection.
• ▸ OpenAI cut Luna’s price by 80% to 20 cents per million input tokens, which makes a plan-with-the-expensive-model, execute-with-the-cheap-one architecture much more compelling.
• ▸ Cheap execution changes the math: three or four passes with a cheap model can cost less than one shot with a frontier model, and one shot is often not enough anyway.
• ▸ Matthias ranks a reliable test harness above a detailed plan — an agent that can run the app end to end and iterate beats one doing a theoretical code review, whatever the model.
• ▸ The 2026-07-28 MCP spec moves to a stateless request/response core and aligns authorization with OAuth 2.0 and OIDC, calling out Entra explicitly.
• ▸ A service principal needs three things and no more: an app registration with a secret, membership in a group allowed to call Fabric public APIs, and access on the workspace. Adding API permissions to the app registration breaks the handshake.
• ▸ Write the .gitignore before the .env file, not after — and note that asking an agent to read .env sends those secrets to the model provider unless the harness redacts them.

Links

• ▸ anthropic.com
• ▸ claude.com
• ▸ daxbench.com