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Sweep 10 Nov 2026 · 02:18Z Build v2.1.322 539 read Stable v2.1.311 Latest v2.1.322 Next v2.1.322 Feeds RSS JSON llms.txt llms-full.txt Unofficial
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Claude Code v2.1.281 ·

MCP discovery cache now keyed on whether the MCP Apps host is enabled

The MCP discovery cache is now kept separately depending on whether the MCP Apps host is enabled

Under the hood No documentation found Internal Changes
JSON All of v2.1.281
Under the hoodTier: how much it should matter to you
2Useful: my rating, 1 to 5
3Signal: worth watching, 1 to 5
MCPArea: what it touches
Internal ChangesKind: in v2.1.281,
Internal ChangesSection of the release

Unclear Whether CLAUDE_CODE_MCP_APPS_HOST is an environment variable or a setting, and how a user turns it on, is not shown.

What

Claude Code saves what it learns from MCP servers (Model Context Protocol servers, which give Claude extra tools) in a discovery cache. The cache is a stored copy, so Claude Code does not have to ask the servers again. The cache's file name and lookup key now record whether the MCP Apps host is enabled, which gives one copy for each case. When a cache entry is written or deleted, both copies are now handled.

CLAUDE_CODE_MCP_APPS_HOST is what turns on the io.modelcontextprotocol/ui extension capability.

Why

When the MCP Apps host is turned on or off, Claude Code no longer reuses discovery results that were saved under the other setting.

Read from
Names in the bundleCLAUDE_CODE_MCP_APPS_HOST
How sure we are
Something disagreesSomething we can check disagrees with this entry, or the writer said they could not settle it.
The writer flagged doubtWhether `CLAUDE_CODE_MCP_APPS_HOST` is an environment variable or a setting, and how a user turns it on, is not shown.
The name it cites is new in this buildNew in this build: CLAUDE_CODE_MCP_APPS_HOST

See this entry in the whole of v2.1.281 →

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