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Claude Code v2.1.120 (auto-updated April 24-25, 2026) introduced a critical regression that broke all --resume and --continue functionality. Two distinct crash modes were reported: (1) REPL mount crash with 'g9H is not a function. (In g9H(K), g9H is undefined)' — caused by an undefined onSessionRestored callback in the REPL component, and (2) 'sandbox required but unavailable' error on resume even when sandbox.enabled=false in settings — caused by the resume code path consulting the sandbox gate before honoring user settings. Both were confirmed cross-platform (macOS, Linux, Windows). Anthropic acknowledged the regression within hours and rolled back the auto-update pointer from v2.1.120 to v2.1.119. Users on v2.1.120 can work around by rolling back to v2.1.119 or using /resume inside a fresh interactive session. The fix shipped in v2.1.121+ (auto-updater restores working version).

On July 23, 2025, all MCP tools in Claude Desktop suddenly stopped working with parameter validation errors. Every tools/call JSON-RPC request was sent WITHOUT the required 'arguments' field, causing all MCP servers to reject tool calls with: 'expected: object, received: undefined' / 'Required' / 'Cannot convert undefined or null to object'. The first tool call in a fresh conversation would work, but all subsequent calls failed because the arguments parameter was stripped from the JSON-RPC params. Affected ALL MCP servers — local filesystem, remote proxies, first-party connectors (Atlassian/Jira, Asana, Slack), and custom MCP servers alike. Root cause: upstream Anthropic API failure on July 23, 2025 that emitted malformed tool-use content blocks without arguments, which Claude Desktop relayed directly to MCP servers. Anthropic staff (ollie-anthropic) confirmed the issue as an 'upstream API failure affecting all MCP tool calls' and deployed a server-side fix within hours, requiring only a Claude Desktop restart. Status page incident: https://status.anthropic.com/incidents/9px1qykyb9w4. Impact: 59 community reactions, 66 comments — a global MCP outage affecting all Claude Desktop users. Agent Decision Tree: (1) Check if this is a historical event — the bug occurred July 23, 2025 and was fixed same day. If user reports are from July 23, 2025, verify with dates. (2) If symptoms match but date is different, this may be a new incident — check https://status.anthropic.com/ for current outages. (3) First diagnostic: inspect MCP server logs for tools/call params. If params contain only '"name":"tool_name"' without '"arguments":{...}', this is the bug. (4) If first call works and subsequent calls fail, this is the classic signature. (5) Apply Solution 1 (restart + fresh conversation). (6) If problem persists after restart, escalate to Anthropic support with MCP server log excerpts.

The Claude Agent SDK (`query()` function) does not read project-scoped MCP servers from `.mcp.json` on startup, even with `settingSources: ['project']`. MCP servers only become available after manually launching `claude` CLI, running `/mcp`, then restarting the SDK. This blocks all non-interactive environments including CI/CD pipelines and automation platforms like Conductor. User-scoped and local-scoped MCPs load correctly — only project-scoped `.mcp.json` is affected. Fix shipped in v2.0.71 (December 16, 2025), confirmed by Anthropic staff assignee ollie-anthropic: 'this should be fixed in the latest release coming out today.'

When Claude Code running in VS Code (v2.1.84 and earlier) gets stuck during a multi-step task, the UI displays "Not responding - try stopping" but provides NO actionable way to stop, cancel, or recover. The session becomes a dead end — users must force-quit VS Code and lose all progress, including completed tasks upstream of the stall. This occurs when a task involves an external operation (e.g., `gh repo create`, network calls) that hangs beyond the backend heartbeat timeout of 60 seconds. The spinner turns red but there is no stop button, cancel button, retry option, or task-skip mechanism. Anthropic staff member qing-ant confirmed the timeout was too aggressive and deployed a fix in the March 27, 2026 release (v2.1.86). The affected version v2.1.84 was published March 25, 2026 and the fix version v2.1.86 was published March 27, 2026 — same day the issue was closed. Latest Claude Code as of June 13, 2026 is v2.1.177.

Claude Code's TUI renderer did not position the terminal's native cursor to follow the text input caret. This broke screen readers (BRLTTY, NVDA, JAWS, VoiceOver, Orca, Narrator) which track the cursor to decide what to display, caused CJK IME preedit/composition text to appear at the bottom-left corner instead of at the insertion point, and prevented screen magnifiers from following user input. The native cursor remained stuck at the bottom of the screen, making it impossible for blind and low-vision users to edit prompts or know where their cursor was. Root cause: the custom TUI renderer uses a full-screen overwrite model where the last render write determines cursor position — the cursor was not declaratively positioned to follow the text input caret. Fixed in v2.1.84 when qing-ant added declarative cursor positioning. Latest version as of June 2026 is v2.1.177.

A regression introduced around 2026-05-20 caused every MCP tool call inside claude.ai scheduled routines to fail with 'Streamable HTTP error: Error POSTing to endpoint: MCP tool call requires approval', silently no-oping all connector-dependent automations. The bug affected 18+ first-party connectors (Slack, Atlassian/Jira, Gmail, Google Calendar, Google Drive, Datadog, Sentry, Notion, Linear, Figma, Amplitude, Guru, Ramp, Zapier, monday.com, Todoist, Snowflake, Microsoft 365) and all custom OAuth MCP connectors. Root cause: the platform's permission model treated interactive approval (call-time 'ask the user') and unattended approval (bind-time grant from routine config) as a single gate, so routines with no human present silently failed. The permitted_tools field on mcp_connections was not being honored as a standing grant for the non-interactive routine surface. Anthropic deployed a platform-side fix within ~10 hours of acknowledgment. Local CLI cron jobs using the same connectors worked throughout as a temporary workaround.