claudekit / updates / claude-code-2-1-154
[ PATCH · ]

Claude Code 2.1.154

Claude Code 2.1.154 brings Opus 4.8 (now defaulting to high effort, with `/effort xhigh` for your hardest tasks) and dynamic workflows (`/workflows`) to Claude Code. Fast mode on Opus 4.8 ships at 2x the standard rate for 2.5x the speed, and the lean system prompt becomes the default for most models. It also adds `! <command>` background shell sessions in `claude agents`, plugin `defaultEnabled: false`, a cleanup-only `/simplify`, and a broad sweep of background-session, security, and terminal-UI bug fixes.

Claude Code
Official announcement →

This article is a summary based on official documentation.

What changed

Claude Code 2.1.154 shipped on May 28, 2026. The headline is that Opus 4.8 and dynamic workflows arrive in Claude Code: Opus 4.8 now defaults to high effort (use /effort xhigh for your hardest tasks), and asking Claude to create a workflow orchestrates work across tens to hundreds of agents in the background, viewable with /workflows. The release also brings cheaper Fast mode on Opus 4.8, the lean system prompt as the default for most models, ! <command> background shell sessions in claude agents, and a broad background-session, security, and terminal-UI bug-fix sweep.

New features

  • Dynamic workflows (/workflows)

    Complex work ran as a single sequential session, so broad tasks were slow. Ask Claude to create a workflow and it orchestrates work across tens to hundreds of agents in the background, so you can take on larger, more complex tasks. Run /workflows to view your runs.

  • Background shell sessions in claude agents (! <command>)

    Running a shell command in the background and reattaching was awkward. In claude agents, type ! <command> to run a shell command as a background session you can attach to and detach from; claude --bg --exec '<command>' does the same.

  • defaultEnabled: false for plugins

    Installing a plugin enabled it outright. Plugins can now declare defaultEnabled: false in plugin.json or a marketplace entry; enable them with /plugin or claude plugin enable. Dependencies of enabled plugins are still enabled automatically.

  • Directory-aware /plugin Discover tab

    The Discover tab now pins plugins whose relevance signals match the current directory with a “suggested for this directory” annotation.

  • Browser selection for Claude in Chrome

    With multiple connected browsers, you can now pick which one to use via /chrome → “Select browser…”, or in-chat when a browser action runs with multiple connected.

Key improvements

  • Opus 4.8 with a new effort default

    Claude Code adds Opus 4.8 support. It defaults to high effort, with /effort xhigh for your hardest tasks.

  • Cheaper Fast mode on Opus 4.8

    Fast mode on Opus 4.8 is now available at a fraction of its previous cost: 2x the standard rate for 2.5x the speed.

  • Lean system prompt by default

    The lean system prompt is now the default for all models except Haiku, Sonnet, and Opus 4.7 and earlier.

  • Fewer unnecessary multiple-choice prompts

    Claude now reserves the multiple-choice question prompt for decisions it genuinely cannot make itself, instead of asking when it already has enough context to proceed.

  • /simplify is now a cleanup-only review

    /simplify now runs a cleanup-only review (reuse, simplification, efficiency, altitude) and applies the fixes, instead of running the full /code-review --fix bug-hunting review.

  • /effort slider relabeled

    The /effort slider labels changed from “Speed”/“Intelligence” to “Faster”/“Smarter” for clarity.

  • Wider agents-view and streaming reach

    ←← to open the agents view now works on Bedrock, Vertex, Foundry, and with telemetry disabled. Streaming tool execution is now always enabled (previously behind a feature flag), including with telemetry disabled or on Bedrock/Vertex/Foundry.

  • MCP behavior

    Stdio MCP server subprocesses now receive CLAUDE_CODE_SESSION_ID and CLAUDECODE=1. claude mcp list/get now show unapproved .mcp.json servers as ⏸ Pending approval instead of auto-approving and connecting when output is piped.

  • claude agents sign-out and Remote Control hint

    In claude agents, /logout now signs you out instead of being sent to a background session, and /remote-control autocomplete shows “Disconnect Remote Control” when Remote Control is already active.

  • Opus 4.8 in the /claude-api skill

    Added Claude Opus 4.8 support and 4.7 → 4.8 migration guidance to the /claude-api skill.

  • Stronger data-exfiltration detection

    Improved the auto-mode classifier’s detection of data exfiltration, particularly bulk transfers of repository contents.

Bug fixes

Security & safety

  • rm -rf $HOME not being blocked as a dangerous path when HOME has a trailing slash — now blocked.
  • $TMPDIR resolving to different directories in sandboxed vs unsandboxed Bash commands within the same session — resolved consistently.
  • Auto mode incorrectly blocking actions with “could not evaluate this action” when the safety classifier ran out of output tokens while reasoning — fixed.
  • A single invalid allowedMcpServers/deniedMcpServers entry in managed settings discarding all managed-settings policy — the bad entry is now dropped with a claude doctor warning.

Background sessions

  • Background-agent completion notifications triggering premature “out of context” behavior on some 1M-context models — fixed.
  • Background-session classifier losing the user’s goal when a scheduled /command fires — fixed.
  • Pinned background sessions respawning every minute after a Claude Code update, causing repeated agent-start notifications and process churn at idle — fixed.
  • Background sessions stuck at “blocked”, “running”, or “working” not retiring after the idle grace period — they now retire.
  • Subagents in background sessions bypassing the worktree-isolation guard and writing to the shared checkout — fixed.
  • Orphaned claude --bg-pty-host processes spinning at 100% CPU after the daemon exits on macOS — fixed.
  • worktree.baseRef: "head" resolving to the main checkout’s HEAD instead of the current worktree’s HEAD when spawning subagents or calling EnterWorktree from inside a linked worktree — fixed.

Terminal & UI

  • Unreadable highlighted-row text in claude agents when the Claude Code theme doesn’t match the terminal background — fixed.
  • Number key shortcuts not working for options shown below the divider in option dialogs — fixed.
  • A stray leading space on wrapped lines when the previous line ended exactly at the terminal width — fixed.
  • Intermittent terminal rendering corruption in VS Code — fixed by capping the number of distinct colors the thinking spinner produces.
  • A phantom expand/click affordance on short ANSI-colored lines that fit on screen — the “ctrl+o to expand” hint no longer shows.
  • The task panel below the prompt showing a stray unselectable “main” row when only a workflow is running — fixed.
  • Plan file names including [Image #N] / [Pasted text #N] placeholders when a plan-mode prompt starts with pasted images or text — fixed.
  • Removed the stale ”& for background” hint from the shortcuts help panel.

MCP & models

  • /mcp tools list and tool detail rendering when MCP servers have long or multi-line tool names or long descriptions — fixed.
  • API 400 errors on models that don’t support the effort parameter when CLAUDE_CODE_ALWAYS_ENABLE_EFFORT is set — fixed.
  • The /model picker not showing fast mode pricing on the Default option for API (pay-as-you-go) users when fast mode is on — fixed.

VS Code & Windows

  • [VS Code] Auto mode no longer requires the bypass-permissions setting to appear in the mode picker, and a dismissable notice on the new-session screen explains auto mode the first time it’s active.
  • [Windows] Update failures caused by claude.exe being in use now tell you to close other sessions and retry instead of showing a generic error.

Notes

  • Opus 4.8 and dynamic workflows have dedicated posts — this entry summarizes them from the Claude Code 2.1.154 release angle; see their own posts for full detail.
  • CLAUDE_CODE_OPUS_4_6_FAST_MODE_OVERRIDE is deprecated — it will be removed on 06/01. To use fast mode on Opus 4.6, switch with /model claude-opus-4-6[1m] and then /fast on.
  • /simplify behavior changed — it now applies cleanup only (reuse, simplification, efficiency, altitude) and no longer hunts for bugs. Use /code-review --fix for bug-hunting.