Stateless MCP and a summer of new models: what changed for builders
A breaking MCP release, a new generation of frontier models and price-performance that keeps falling. Our notes on what to change in production systems, and what to leave alone.
It has been a busy summer for anyone who builds on top of frontier models. Here is what we think matters for production systems.
MCP went stateless
The 2026-07-28 MCP specification is the biggest change to the protocol since launch. The lead maintainers describe a stateless protocol core: the initialize handshake and session header are gone, so any request can hit any server instance. It also adds a formal extensions framework, MCP Apps (sandboxed, server-rendered interfaces), hardened OAuth and OIDC authorisation, and deprecates roots, sampling and logging. Simon Willison called it "the most significant change to the MCP spec since it first launched."
For enterprise deployments, stateless is good news. MCP servers can now sit behind an ordinary load balancer and scale like any other API. The cost is a migration: servers and clients built on the old session model need updating.
What we are doing: upgrading the connectors we maintain, with each server's test suite run against both spec versions during the transition.
A new model generation
Anthropic's release notes list Claude Fable 5 (June 9), Claude Sonnet 5, described as its most agentic Sonnet yet (June 30), and Claude Opus 5, close to Fable 5's intelligence at half the price (July 24). OpenAI and Google shipped new models over the same weeks.
What we are doing: nothing dramatic. Every agent we run has an evaluation set, so a new model is a candidate, not a migration. We run the set, compare quality and cost per case, and switch only where the numbers say so. Usually a cheaper tier now matches what the more expensive one did a few months ago, and that is where the savings come from.
The lesson of the summer
The ecosystem is moving faster than any single integration can keep up with. Systems survive it when:
- connectors follow a standard and have their own tests,
- models are swappable behind an evaluation gate,
- prompts, tools and model versions are versioned together,
- someone owns the upgrade calendar.
None of this is glamorous. It is why a summer of releases was an opportunity for our clients rather than an outage.
Sources
- The 2026-07-28 MCP Specification Release Candidate, Model Context Protocol blog, May 21, 2026.
- Stateless MCP has recaptured my interest, Simon Willison, July 31, 2026.
- Claude release notes, Anthropic.