mcp

ModelContextProtocol 2.4.0 ships ModelContextProtocol.Extensions.Skills, an experimental package that implements the SEP-2640 Skills extension: one call to publish a folder of SKILL.md directories, and client helpers that verify every file against a SHA-256 manifest.

ACP (Agent Client Protocol, v1) connects an editor to a coding agent; MCP (spec 2026-07-28) connects an agent to tools. They sit on opposite sides of the agent and are used together: ACP's session/new even carries the MCP servers the agent should start. Here is the feature matrix, the wire flow, and a working agent and client checked against @agentclientprotocol/sdk 2.4.0.

The MCP Tasks extension (io.modelcontextprotocol/tasks, spec 2026-07-28, SEP-2663) lets a server answer tools/call with a durable task handle instead of a result. The client polls tasks/get, answers mid-flight questions with tasks/update, and can cancel or reconnect. Here is the wire protocol, what changed from the experimental 2025-11-25 version, when a task is worth it, and a working server and client checked against @modelcontextprotocol/ext-tasks 0.2.2.

If a specialist agent is just a model loop wrapped around a few read-only calls into your own services, collapse it into a skill served over MCP: a SKILL.md plus typed tools that the parent model calls directly. Keep it an A2A agent when it needs its own model, private context, a long multi-step workflow or an independent lifecycle. Here is the decision matrix, the measured cost of each path, and the Agent Framework 1.17 wiring.

ModelContextProtocol 2.3.0, released October 20, 2026, changes McpClient.ServerInfo from Implementation to Implementation? because 2026-07-28 servers may omit their identity from server/discover. Here is why, what breaks under warnings-as-errors, and the one-line fix.

Wire Cursor Rollouts (launched September 23, 2026) to your CI and to Datadog so every PR, including the ones a cloud agent wrote, gets a rollout plan before merge and per-environment checks at deploy, 20 minutes, 1 hour, 1 day and 3 days. Covers the DeploymentsService API, a GitHub Actions job, the Datadog MCP data source, and the gotchas that leave changes stuck in Pending.

Azure MCP Server 3.0.0 shipped on October 12, 2026. Tool calls with unknown parameters now fail, options like subscription and tenant were removed from many tools, new Storage accounts disable Shared Key auth, and the server speaks the stateless MCP 2026-07-28 protocol.

The GitHub Copilot SDK (1.0.18, October 8, 2026) is a thin client for the Copilot CLI runtime: your app speaks JSON-RPC to the same agent loop that powers Copilot CLI, with built-in file and shell tools, MCP, sub-agents, hooks, and BYOK. How it is wired, four things you can build with it, and the defaults that will bite you in production.

MCP is a JSON-RPC protocol that lets any AI host call tools, read resources and use prompts from any server, the way LSP did for language support. Here is how it works on the wire under revision 2026-07-28, captured from a real server, and why VS Code, Visual Studio, JetBrains, Xcode, Zed and Cursor all converged on it.

Every agent request pays for its system prompt, the provider's hidden tool-use preamble, and every tool schema before the user says anything. How to measure that fixed cost with differential count_tokens calls on the Anthropic API, the input_tokens endpoint on OpenAI, an MCP listTools probe, and /context in Claude Code, anchored to claude-opus-5-5, claude-sonnet-5, and @modelcontextprotocol/client 2.1.0.