Claude Code adds Mods, and 1M context becomes the default
Claude Code v2.1.287 adds Claude Mods, letting plugins modify deeper behavior. It ships one built-in mod, "You should know": a side agent watches the session and flags things you or Claude might miss, enabled with /plugin enable cc-plugin-you-should-know@builtin for first-party sessions with telemetry on. Opus 4.7+ and Fable now default to a 1M context window on Bedrock, Vertex, Foundry and the Claude apps gateway, with no [1m] suffix, and CLAUDE_CODE_DISABLE_1M_CONTEXT=1 keeps 200K. MCP servers set to alwaysLoad: false now defer all of that server's tools behind tool search. VSCode adds "Run in background" for a running command or sub-agent.
Two things to check before you upgrade. If an MCP server stops connecting afterwards, add "bareElicitationCapability": true to its config entry, since the 2025-11-25 protocol now carries URL prompts, for example to sign in. And because plugins can now reach deeper into the agent, read what a third-party plugin actually does before you install it on a work machine.