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Fast mode on Opus 4.8 is deprecated, removal set for November 30

If you still run fast mode on Opus 4.8, it is deprecated as of October 30 and goes away on November 30. After that date your fast mode requests return an error rather than falling back to standard Opus 4.8, so you'll want to move to Opus 5.5 to keep the speedup.

Worth Knowing

Ultrathink now raises a turn to xhigh effort

Typing ultrathink in the terminal runs that turn at xhigh effort on Opus 5.5, Sonnet 5.5, Haiku 5.5 and Fable 5.1, and typing it mid-turn raises the remainder. VS Code matches the terminal behavior including the rainbow styling, and CLAUDE_CODE_DISABLE_ULTRATHINK turns the keyword off entirely.

New setting blocks writes outside your working directories

Setting permissions.blockWritesOutsideWorkingDirectories makes Write, Edit and NotebookEdit refuse any path outside your working directories, in every permission mode including auto. It's the write-side counterpart to the existing read restriction.

Idle compaction comes to VS Code and Claude Desktop

A conversation over 200K tokens that you leave idle is now summarized in the background, and the summary is used on your next message if the prompt cache has expired. Idle compaction also now runs for subscribers with telemetry off, and on Bedrock, Vertex, Foundry and LLM gateways once the one-hour prompt cache is on.

Timed-out shell commands now return partial output

When a Bash command hits its timeout, you get the output produced so far plus a note that the command is still running in the background, instead of an empty result.

VS Code adds syntax coloring to reply code blocks

Code blocks in Claude's replies are now syntax highlighted in the VS Code panel across light, dark and high contrast dark themes. The panel also gained a spinner for slow UserPromptSubmit hooks and a fix for Ctrl+D dictation under non-Latin keyboard layouts.

Under the Hood

Faster startup, fewer freezes, lower memory in long runs

Pro and Max launches skip two network requests within an hour of the last check, long list items in CLAUDE.md no longer cause startup freezes, and long headless and SDK turns with many subagents use less memory since the parent no longer holds every subagent's tool results. /context is also faster in sessions with ten thousand or more MCP tools.

Orphaned shells, context errors and search hangs fixed

Shell commands no longer keep running on macOS and Linux after Claude Code exits on its own, standard-context sessions that run past 200K tokens now compact and continue instead of erroring about 1M context credits, and Grep and Glob no longer hang on Windows when the search process is killed at the timeout but doesn't exit.

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