Main Updates in Claude Code v2.1.153

This is Ishikawa from the Cloud Business Division. Claude Code v2.1.153 (released 2026-05-27) has been released. This update focuses primarily on stabilizing background sessions and claude agents (background agents), and includes security fixes for MCP and authentication, as well as a behavioral change for /model.

Update Summary

v2.1.153 lists 36 changes in the CHANGELOG. New features are relatively few, with the majority being bug fixes around background sessions and claude agents (background agents). It also includes security fixes for MCP server and API gateway authentication, and a behavioral change regarding default saving for /model.

Notable Updates

• New Features
  • A skipLfs option has been added to the github/git plugin marketplace sources, allowing Git LFS downloads to be skipped.
  • COLUMNS and LINES environment variables are now passed to status line commands, enabling output adjustment based on terminal width.
• Bug Fixes
  • Fixed an issue where memory usage would reach several GB when resuming sessions on machines with many saved sessions.
  • Fixed an issue where the Agent tool with subagent_type: 'claude' would operate in a temporary worktree and silently discard output to gitignore-targeted paths.
• Security
  • Fixed a regression where a user's Anthropic OAuth credentials were being incorrectly sent to custom API gateways.
  • Fixed an issue where MCP servers defined in subagent frontmatter were ignoring --strict-mcp-config and enterprise management policies.

Update Details

New Features

• A skipLfs option has been added to the github/git plugin marketplace sources. Git LFS downloads can now be skipped during clone and update operations.
• COLUMNS and LINES environment variables are now passed to status line commands. Scripts can now adjust output size to match terminal width.

Improvements

• A one-time notification is now displayed when npm global installation cannot be auto-updated. Remediation steps are listed in /doctor.
• The autocomplete for claude agents dispatch input now suggests native slash commands and bundled skills in addition to project skills.
• The PR column in claude agents now displays PR #N for a single PR and N PRs for multiple PRs.
• claude doctor now displays the results of the most recent update attempt.
• The startup notifications for "authentication required" that were previously displayed separately for MCP servers and connectors have been consolidated into a single message.
• On macOS, background agents now appear as "Claude Code" in Privacy & Security, and retain previously granted permissions after upgrades.

Security

• Fixed a regression where custom API gateways were receiving the user's Anthropic OAuth credentials instead of the gateway's own token.
• Fixed an issue where MCP servers defined in subagent (Agent tool) frontmatter were ignoring --strict-mcp-config, --bare, remote mode, enterprise managed MCP configuration, and managed-settings MCP server allow/deny policies. This affects environments using enterprise management policies.
• --strict-mcp-config no longer removes inline mcpServers from explicitly passed agent definitions (--agents / SDK agents). Additionally, blocked subagent MCP servers are now displayed as warnings.

Fixes

• Fixed stateful MCP server reconnection loop: Fixed an issue (regression in v2.1.147) where stateful MCP servers without an optional GET SSE stream would fall into a reconnection loop on tools/list.
• Fixed excessive memory usage during session resume: Fixed an issue where memory usage would reach several GB when resuming by specifying a transcript file path on machines with many saved sessions.
• Fixed subagent output being discarded: Fixed an issue where the Agent tool with subagent_type: 'claude' was running inside an undocumented temporary worktree, silently discarding output to gitignored paths. If you have subagents generating files to gitignored paths, you may have been affected, so we recommend checking.
• Fixed claude update ignoring release channel: Fixed an issue where claude update for npm installations would install the latest version instead of the version for the configured release channel.
• Fixed false success display in Windows PowerShell installer: Fixed an issue where "Installation complete!" was displayed even when installation had actually failed.
• Fixed exit hang in stream-json mode: Fixed an issue where the CLI would fail to exit and hang when stdin was closed without EOF, leaving behind stale session markers.
• Fixed response loss when using /bg during a response: Running /bg while Claude is responding now causes the response to continue in the background session rather than being discarded.
• Improved rollback on Windows update failure: When a Windows update fails, the original executable is now restored from a copy and recovery instructions are provided.
• Fixed process lingering on VS Code exit on Windows: Fixed an issue where Claude Code processes would not exit cleanly when VS Code was closed, causing false "unclean exit" reports and leaving behind MCP servers.
• In addition, numerous minor bug fixes have been made, including file:// link clicking, claude --help line wrapping, MCP tool progress display, background session operations such as /btw, /copy, and /rename, Windows IME candidate window positioning, and terminal redraws and background colors.

Breaking Changes / Behavioral Changes

The behavior of /model has changed. If you are using the default key bindings, the new behavior will be applied automatically, but if you have customized your key bindings, manual action is required.

• Selections made in /model are now saved as the default for new sessions (aligning with IDE behavior). To switch models for the current session only, press s in the picker.
• Accordingly, if you have customized the key binding for modelPicker:setAsDefault, you need to rename it to modelPicker:thisSessionOnly in keybindings.json (the d action has been replaced with s).

Closing

v2.1.153 is a release focused on stabilizing background sessions and claude agents, along with security fixes for MCP and authentication. In particular, for enterprise environments using managed MCP policies, the fix to MCP server behavior via subagents is important. Since fixes related to credential handling are also included, we recommend updating promptly for configurations using custom API gateways or subagent MCP. Also, since the behavior of /model has changed, those who have customized their key bindings should verify their configuration.

Recent Updates

https://dev.classmethod.jp/articles/20260524-claude-code-updates-v2-1-150/

https://dev.classmethod.jp/articles/20260524-claude-code-updates-v2-1-152/

References

https://github.com/anthropics/claude-code/blob/main/CHANGELOG.md

https://code.claude.com/docs/en/changelog