Claude Code 2.1.316 sets an end date for fast mode on Opus 4.8
Claude Code 2.1.316 deprecates fast mode on Opus 4.8: from November 30, 2026 those requests return an error instead of falling back. The same week brought a switch that turns ultrathink off, an effort setting for subagents, a setting that blocks writes outside your project, and a prompt before a tool call sends your account email anywhere.
What happened
Anthropic shipped four Claude Code releases in five days. On npm, 2.1.314 appeared on October 29 (Pacific time), 2.1.315 and 2.1.316 on October 30, and 2.1.317 on November 2. The changelog has no section for 2.1.315. Everything below comes from the Claude Code changelog.
Fast mode on Opus 4.8 ends November 30
Since October 30, fast mode for Opus 4.8 is deprecated, and on November 30 it's removed. After that date a fast mode request on Opus 4.8 returns an error. It doesn't drop to standard-speed Opus 4.8, so a script or CI job pinned to that pair will fail outright. The changelog's advice is to move to Opus 5.5 to keep the speedup.
New switches
| Setting | Version | What it does |
|---|---|---|
CLAUDE_CODE_DISABLE_ULTRATHINK | 2.1.316 | Turns the ultrathink keyword off, so the word stays plain text |
CLAUDE_CODE_SUBAGENT_EFFORT | 2.1.316 | Effort level for subagents when nothing else names one, instead of the session's |
permissions.blockWritesOutsideWorkingDirectories | 2.1.314 | Write, Edit and NotebookEdit refuse paths outside the working directories, in every permission mode |
A related change in 2.1.317: a subagent on a different model from the main conversation now runs at that model's saved effort level, or its default, rather than inheriting the session's. If you run the main session at high effort and send subagents to a cheaper model, they no longer pick up the high setting by accident. More on that split in our guide to Claude Code subagents.
The write fence goes in settings.json:
{
"permissions": {
"blockWritesOutsideWorkingDirectories": true
}
}Smaller changes you'll notice
- An email check (2.1.317). Claude Code asks before a web or shell tool call sends your account email address over the network.
- Idle compaction (2.1.314). In VS Code and the desktop app's Code tab, a conversation over 200K tokens that sits idle gets summarized, and the summary is used on your next message if the prompt cache has expired.
- Re-reading a file returns it (2.1.317). The Read tool no longer answers "file unchanged since your last Read"; it returns the content again.
- Ctrl+C is safer (2.1.317). Pressing it to clear typed text at the prompt no longer stops every running background agent.
- /schedule warns about connectors (2.1.317) when a new cloud scheduled task gets connectors you didn't ask for, and says how to remove them.
What it means for you
- You use fast mode: search your settings, scripts and CI for Opus 4.8 model IDs used with fast mode, and move them to Opus 5.5 before November 30.
- You share a machine or run Claude Code in auto mode: turn on the write fence so edits stay inside the project folders.
- Ultrathink fires when you don't want it (the word sits in your prompts or templates): set
CLAUDE_CODE_DISABLE_ULTRATHINK=1. The 2.1.311 change that made ultrathink raise effort explains when it triggers.
Run claude update to get 2.1.317.
Sources
- anthropics/claude-code, CHANGELOG.md, entries 2.1.314, 2.1.316 and 2.1.317, checked November 3, 2026
- npm, @anthropic-ai/claude-code versions, checked November 3, 2026