Claude Code v2.1.311: xhigh ultrathink, 200K-token fix

Anthropic released Claude Code v2.1.311 on October 26, 2026, introducing a significant upgrade to the ultrathink feature and resolving critical issues affecting long-context sessions. Notable updates include ultrathink now running turns at xhigh effort, while the release also fixes failures that previously halted standard-context sessions when exceeding 200,000 tokens.

Claude Code v2.1.311 (released October 26, 2026) represents one of the platform’s most substantial updates, with 92 changes, including 56 fixes, 17 improvements, 10 developer experience changes, 5 new features, 3 performance improvements, and 1 breaking change.

Ultrathink Gets Major Effort-Level Upgrade

The headline feature of this release transforms how ultrathink functions within Claude Code. Using ultrathink in an interactive terminal now runs that turn with xhigh effort for Opus 5.5, Sonnet 5.5, Haiku 5.5, and Fable 5.1 via the Anthropic API. If entered while Claude is working, it raises the effort for the remainder of that turn.

Additionally, the rainbow display for ultrathink now only appears in places where the keyword can raise the effort, and will no longer appear inside quotation marks or as part of file paths. This visual refinement helps developers understand when the feature is actively available.

Interestingly, as of the time of writing (October 27, 2026), the official documentation (Model configuration) still states that ultrathink adds context instructions to the prompt and does not change the effort level sent to the API, suggesting the documentation has not yet caught up with this implementation change.

Critical Context Management Fixes

Version 2.1.311 addresses a critical problem that affected users working with large conversational contexts. Fixed standard-context sessions stopping with “Usage credits required for 1M context” when a request ran over 200K tokens; Claude Code now compacts the conversation and continues.

This compaction improvement ensures sessions can continue smoothly without unexpected interruptions, a crucial enhancement for developers working on complex, long-running coding tasks.

Enhanced Performance and Reliability

The release includes several performance and stability improvements across different aspects of the platform:

Fixed Write and Edit stalling for up to 5 seconds after they ran, and reporting 0 lines changed, when changing thousands of lines in a file
Fixed interrupting Claude not taking effect until a timeout while an MCP server had not answered a resource read or a skill was still downloading
Fixed subagents being unable to use MCP tools from servers that finish connecting after the subagent starts
Fixed long freezes at startup and after reading or editing files when a CLAUDE.md file holds a very long list item

New Self-Hosted Runner Features

For users running self-hosted environments, the update brings new control options. Added –hold-idle-file and –max-hold-min to self-hosted-runner, to keep an idle session while your host reports processes it left running.

User Experience Improvements

The release includes several refinements aimed at improving the overall user experience:

Improved the message shown when a pasted sign-in code is refused: it now says the code may have expired or been used, and to sign in again
Improved Slack connector sends: Claude now checks a channel’s topic for posting rules before messaging a channel you didn’t name
Improved screen reader mode: Claude’s questions are listed as “Questions: Color (answered), Pages”, without arrows or symbols
Added a tip for the Explanatory output style, shown when you ask Claude for explanations

Model Naming Simplification

Changed model names and IDs to drop the [1m] suffix and its label on models where the suffix has no effect; the suffix is still accepted. This change streamlines the model selection interface while maintaining backward compatibility.

Additional Technical Fixes

Beyond the major updates, v2.1.311 resolves several edge-case issues:

Fixed Claude seeing stale MEMORY.md and CLAUDE.md content right after automatic compaction when those files were edited earlier in the session
Fixed claude -p and SDK sessions saving transcript messages out of order or keeping messages that were taken back
Fixed SubagentStop hooks running about twice a minute for each running subagent instead of once when it finishes
Fixed messages that Claude sends to a cloud or Remote Control session appearing as your own message in the Claude mobile apps

Context: Claude Code’s Growing Impact

This update arrives as Claude Code continues to gain traction in the enterprise market. Recent reporting indicates that Anthropic’s IPO filing highlights Claude Code as a major revenue driver, with top enterprise users of the coding tool spending significantly more than non-coding customers.

The platform has evolved from an internal command-line tool into a full-featured coding agent, and these continuous improvements demonstrate Anthropic’s commitment to refining the developer experience based on real-world usage patterns.

Key Facts

Claude Code v2.1.311 was released on October 26, 2026
The release includes 92 total changes across fixes, improvements, and new features
ultrathink now triggers xhigh effort levels for supported models via the Anthropic API
Sessions can now automatically compact conversations and continue beyond 200K tokens
Write and Edit operations no longer stall for up to 5 seconds when modifying thousands of lines
New --hold-idle-file and --max-hold-min flags added for self-hosted runners

Sources

Written by

Mike Gingerich

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Author: Mike Gingerich, President of web firm Digital Hill, Co-Founder of TabSite .
Digital and Social Media Marketer, Speaker, and Business Consultant. Part geek, part marketer, total digital junkie! Seeking to add value, make the complex simple, and leave a positive impact.

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