日本語サマリー

Claude Code 2.1.251 リリースノート要約

⚠️ 重要なセキュリティ修正・破壊的変更

• シンボリックリンク回避による権限チェック迂回を修正： ワーキングディレクトリ内で symlink が差し替えられた際、Read/Write/Edit が許可外の場所にアクセス可能だった問題。Grep/Glob の Read(...) deny ルール回避も修正
• プラグインコマンドのパストラバーサルを修正： プラグインディレクトリ外を指すパスを拒否するよう変更
• プロジェクト設定の権限昇格を修正： プロジェクト設定でベータトレーシングや生 API ボディログを有効化できた問題、および OTLP コレクターのバイパスを修正
• サンドボックス内 Bash 出力ファイルの作成・読み取り方法を変更： サンドボックス化されたコマンドがファイルをリダイレクト・置換できないように
• ANTHROPIC_CUSTOM_HEADERS が認証情報やルーティング系ヘッダー（Authorization, Host など）を設定する場合、承認を必須に変更
• プロジェクト設定の env で CLAUDE_CONFIG_DIR, CLAUDE_CODE_TMPDIR, TMPDIR/TMP/TEMP を設定できなくなった破壊的変更（shell・user・managed settings で設定する必要あり）

新機能

• PreModelSwitch / PostModelSwitch フックイベントを追加。モデル切り替えを block・confirm・annotate 可能に
• フォアグラウンド subagent のツール呼び出しを Remote Control クライアントにライブストリーミング
• /usage に Spend limit バー、rate_limits.spend_limit status line フィールドを追加
• /cost にプロンプトキャッシュの行（ヒット率、misses、warm/cold）と prompt_cache オブジェクトを追加

主な仕様変更

• CLAUDE_CODE_SUBAGENT_MODEL はデフォルト値として機能するように変更（agent 定義の model: や spawn 時の明示指定が優先）
• Claude 以外のモデルではコミットトレーラーが Co-Authored-By: Claude Code に
• seat ベースの Enterprise サブスクリプションのデフォルトモデルが Opus 5 に
• /effort がモデルごとに effort レベルを保存するように
• Claude in Chrome のブラウザ操作が常に Claude Code の権限チェックを通るように

その他の notable な修正

• Bash 権限チェックが OPTIND=1/0 のような算術式代入を自動承認していた問題を修正（承認プロンプトを出すように）
• thinking のみの出力後に「text content blocks must be non-empty」で会話が固まる問題を修正
• tmux/SSH 上のバックグラウンドセッションでのテキスト選択、GNU screen でのイタリック表示などを修正
• サンドボックス隔離を弱める server-managed settings に承認を必須化
• バイナリサイズを約 7.5 MB 削減（使用頻度の低い6言語のシンタックスハイライト削除を含む）

原文（Release Notes）

What's changed

• Added PreModelSwitch and PostModelSwitch hook events (block, confirm, or annotate a model switch); SessionStart resume hooks now receive session staleness and the estimated re-cache cost
• Added live streaming of a foreground subagent's tool calls and results to Remote Control clients (background subagents, the default, still show status only)
• Added a Spend limit bar to /usage and a rate_limits.spend_limit status line field for developers behind a Claude apps gateway with spend limits
• Added a per-session prompt-cache line to /cost (hit ratio, misses, tokens re-cached, warm/cold) and a matching prompt_cache object for status line scripts
• Added attach, logs, stop, respawn, and rm to claude --help; the --resume message for a running background session now names the exact claude attach <id> command
• Fixed file tools (Read, Write, Edit) following a symlink swapped inside the working directory after the permission check, which could read or write outside the approved location
• Fixed plugin commands declared in a marketplace entry being able to point outside the plugin directory; such paths are now rejected with a path-traversal error
• Fixed project settings being able to enable detailed beta tracing or raw API body logging, and a lower-scope beta tracing endpoint bypassing an OTLP collector pinned by managed settings or a host app
• Fixed the Workflow tool reading (and quoting in errors) a scriptPath outside what the session may read before the permission check ran
• Fixed Grep and Glob not applying Read(...) deny rules to files reached through a symlinked search path
• Fixed conversations getting stuck on "text content blocks must be non-empty" errors after a turn where the model produced only thinking
• Fixed the first launch on a fresh install starting in default mode instead of auto mode for accounts whose startup default is auto mode
• Fixed Opus 5 requests failing with "effort … is not supported when thinking is disabled" when effort was xhigh/max and thinking was turned off; effort is now sent as high in that case
• Fixed replying to a message Claude Desktop delivered from another session: SendMessage to that session id now delivers through Claude Desktop instead of failing with "not reachable"
• Fixed TUI lag with many parallel subagents: per-second progress ticks now replace their predecessor instead of piling up in the transcript
• Fixed agent teams: a teammate's final answer not reaching the team lead — it now arrives in the idle notification instead of a content-free "available" notice
• Fixed background subagents being unable to reply to a message from an unnamed sibling or parent agent (from was the agent type, which is not an address)
• Fixed managed-settings disableAutoMode arriving mid-session not moving an already-running auto-mode session back to default mode
• Fixed a "switch to Opus 1M for 5x more context" tip that appeared even when the current Opus model already has a 1M context window
• Fixed Claude apps gateway sessions treating a stored Anthropic profile (e.g. a Console sign-in) as active: listing it in /status and retrying gateway 401s with it, though requests never use it
• Fixed cloud sessions telling Claude the model had changed when the host was only setting the session's initial model
• Fixed Remote Control reporting a failure when an organization's policy disables it; it now shows a single quiet notice instead
• Fixed /mcp reconnect on Remote Control showing a generic withheld-detail error instead of the real remedy when a server was disabled in another session
• Fixed --input-format stream-json: client-injected assistant tool calls sent without a message id were merged into the first one and their results lost, including when resuming older sessions
• Fixed session transcripts being silently overwritten when a directory change relocated a session onto an existing same-ID transcript
• Fixed background sessions and their subagents being unable to edit files inside a git worktree they created with git worktree add
• Fixed background sessions occasionally starting without any plugin skills (and staying that way) when another Claude Code process was refreshing the plugin marketplace at the same moment
• Fixed selecting text in an opened background session inside tmux over SSH: it now copies to the tmux buffer like a foreground session instead of falling back to OSC 52
• Fixed SDK and cloud sessions hanging indefinitely when an SDK MCP server's handshake acknowledgment was lost; the wait now times out after 70 seconds and marks only that server failed
• Fixed self-hosted runner leaving a stuck session's Bash tool processes running after the session was force-stopped
• Fixed /usage-credits for Team and Enterprise members whose admin set the org's usage-credit limit to $0: it now offers to ask the admin instead of saying a cap was reached
• Fixed --worktree --tmux with a merge-request number on a gitlab.com origin trying a doomed GitHub-style fetch first instead of fetching the GitLab ref directly
• Fixed Ctrl+G failing with "Emacs quit unexpectedly" in background sessions for editors that open /dev/tty, such as emacs -nw and micro
• Fixed an additionalDirectories entry containing a null byte crashing startup, or breaking /add-dir and later settings updates when it came from an SDK host, IDE, or hook; it is now skipped
• Fixed the MCP server menu's copy shortcut: it now says how the sign-in URL was copied instead of always claiming success
• Fixed italic text (such as the session recap line) rendering as highlighted blocks in GNU screen and in tmux sessions using a screen terminal type
• Fixed claude mcp add --header and claude mcp add-json help text naming the wrong transports
• Fixed claude ultrareview and /ultrareview waiting the full 30 minutes when the cloud session fails to start; they now stop early and report the reason
• Fixed Bash permission checks auto-approving commands that assign an arithmetic expression to an integer shell variable (e.g. OPTIND=1/0, RANDOM=2+2); these now prompt for approval
• Fixed backgrounded sessions (←, /background, --bg) losing a Vertex/Bedrock gateway (ANTHROPIC_*_BASE_URL + CLAUDE_CODE_SKIP_*_AUTH) exported in the shell, so every request failed
• Fixed claude --bg --model fable on Max plans stopping to ask for usage credits while the interactive session on the same account still had Fable allowance
• Fixed the one-time "make auto mode your default" offer appearing in unattended sessions (e.g. agent-team teammate panes), where a stray keypress could accept it unread
• Fixed the managed-settings approval prompt re-appearing after signing in again to the same Claude apps gateway when the settings are unchanged
• Fixed disabled /bug and /share reporting that /feedback was disabled; tips, /help, and refusal messages no longer suggest /feedback when an org policy or env var turns it off
• Fixed cloud session creation advising GitHub setup after a transient GitHub connection failure — the message now says to retry instead
• Improved CPU usage during turns in interactive sessions by cutting redundant UI re-renders
• Improved install size: the native binary is about 5 MB smaller
• Improved cloud sessions: when the session's network proxy drops a connection during a Bash command, the tool result now names the host and reason instead of only "connection reset"
• Improved /schedule to explain that MCP servers configured in Claude Code can't be attached to cloud routines, instead of a bare "No MCP connectors" message
• Improved framing of messages from your own subagents: Claude is told the sender is a worker inside this session, not an unrelated Claude session
• Improved the prompt placeholder to read "Message @name…" while viewing a background subagent or fork transcript opened from the subagent panel or /tasks
• Improved sanitization of MCP server names in error messages, menus, and command results
• Improved Amazon Bedrock session start under CLAUDE_CODE_PROVIDER_MANAGED_BY_HOST (e.g. Claude Desktop): a session given a Bedrock model ID or ARN no longer waits for inference-profile discovery
• Improved the managed settings approval dialog to list only the settings that changed since you last approved them
• Improved retry when the model's tool call is malformed: the broken output is now dropped from the retry context, including on Bedrock, Vertex, and Foundry
• Changed /radio to be available on Bedrock, Vertex AI, Foundry, and Claude Platform on AWS, and when telemetry is disabled
• Changed Claude in Chrome so browser actions always go through Claude Code's permission checks, including in sessions with telemetry disabled, which previously used the Chrome extension's own prompts
• Changed CLAUDE_CODE_SUBAGENT_MODEL to set the default subagent model rather than override everything: an agent definition's model: and an explicit per-spawn model now take precedence over it
• Changed the default commit trailer to Co-Authored-By: Claude Code when the active model isn't a recognized Claude model (e.g. third-party models behind a custom ANTHROPIC_BASE_URL)
• Changed the default model for seat-based Enterprise subscriptions to Opus 5, matching other premium plans
• Changed /effort to save your default effort level per model, so each model keeps its own setting when you switch
• Changed analytics to no longer turn off before sign-in solely because managed settings force gateway login (or cannot be read); they stay off once signed in to the gateway or via DISABLE_TELEMETRY
• Changed the footer PR badge on Bedrock, Vertex, and Foundry, and when telemetry is off, to call the GitHub API directly (via gh auth token, GH_TOKEN, or GITHUB_TOKEN) instead of gh pr view
• Changed how Bash command output files are created and read back when commands run in the sandbox, so a sandboxed command cannot redirect or replace them
• Changed plugin/LSP install suggestions and the auto-mode default offer to wait until you've sent or cleared what you're typing, so the Enter that sends your prompt can't answer them
• Changed server-managed settings that terminate sandbox TLS, route sandbox traffic through your own proxy, inject credentials, or weaken sandbox isolation to require approval before they apply
• Changed ANTHROPIC_CUSTOM_HEADERS from managed or project settings to require approval when it sets a credential, org/tenant, routing, or API-behavior header (e.g. Authorization, Host)
• Changed project-level .claude/settings.json env to no longer set CLAUDE_CONFIG_DIR, CLAUDE_CODE_TMPDIR, or TMPDIR/TMP/TEMP; set them in your shell, user, or managed settings instead
• Removed syntax highlighting for six rarely used languages (1c, gml, isbl, mathematica, maxima, sqf); the binary is 2.5 MB smaller
• [VSCode] Fixed the sign-in screen's "Bedrock, Foundry, or Vertex" button opening the docs at the top of the page instead of the third-party provider setup section
• [VSCode] Changed the Remote Control banner to a footer pill (shown while Remote Control is on or has failed) that opens the session on claude.ai/code; turn it on or off with /remote-control