Claude Code ships idle compaction to beat the 1-hour cache expiry
Back-to-back 2.1.299 and 2.1.300 drops add /effort and /fast to agent view, gzip requests by default, and quietly tighten MCP allow rules.
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Idle compaction beats the cache clock
Conversations over 200K tokens that sit idle for about 54 minutes now get compacted before the one-hour prompt cache expires, so your next message doesn't pay to rebuild context. Turn it off with `{"idleCompaction": false}` or move the floor with `CLAUDE_CODE_IDLE_COMPACT_MIN_TOKENS`.
/effort and /fast land in agent view
You can now flip reasoning effort or fast mode mid-session straight from agent view, and a bare `/model`, `/effort`, or `/fast` opens a picker. New `/usage` warnings also flag when max effort, workflows, or always-on context are quietly eating your quota.
MCP allow rules got stricter — audit yours
A breaking change: `mcp__a` no longer covers a server named `a__b`. Allow rules now match only the exact named server, so use `mcp__<server>__*` with the full normalized name or tools you expected to be permitted will silently stop matching.
Requests now gzip by default
Large requests to api.anthropic.com are gzip-compressed automatically; opt out with `CLAUDE_CODE_GZIP_REQUEST_BODIES=0`. Paired with Sonnet 5.5 cache reads dropping to $0.10/M earlier this week, big-context sessions get noticeably cheaper to run.
@ mentions can pass paths, not file dumps
Set `CLAUDE_CODE_DISABLE_FILE_MENTIONS` and `@` file mentions hand Claude the file path instead of dumping the whole file into context — a cheap way to keep large files out of your window until Claude actually decides to read them.
New /advisor tool and prompt-box hooks
`/advisor` arrives on Claude Platform on AWS (disable with `CLAUDE_CODE_DISABLE_ADVISOR_TOOL=1`), alongside a `prompt.change` mod hook and `virtualText` decorations that draw hints in the prompt box without touching your draft. `UserPromptSubmit` hooks now run before skill and command expansion.