MCP client fixes and known issues
If you are running into MCP problems with Claude, Cursor, or Codex, this page lists the open known issues and the recent releases that fixed them.
At a glance
| Client | Open known issues | Most recent entry | Details |
|---|---|---|---|
| Claude | Tool names over 64 chars break the session | 2.1.219 2026-07-24 | Claude issues |
| Cursor | One-click install button broken (3.14.x–3.15.6) | 3.10 2026-06-30 | Cursor issues |
| Codex | codex mcp login fails on macOS | rust-v0.145.0 2026-07-21 | Codex issues |
Open known issues
Claude: tool names exceeding 64 characters break the Claude session, from 2026-07-28. Claude enforces a 64-character limit on tool names, which does not comply with the 128-character maximum the MCP specification defines. When any connected server exposes a tool whose name exceeds 64 characters, Claude rejects the connection and the entire session stops working. Use tool name customization to alias affected names to 64 characters or fewer.
Codex: codex mcp login fails with "No authorization support detected" on macOS, from 2026-07-22. Against the same spec-compliant OAuth MCP server, one Codex version completes login on Linux but fails discovery on macOS. Reach the server through an mcp-remote stdio bridge, which moves the OAuth flow out of Codex. Tracked in openai/codex#34684.
Cursor: one-click MCP install button broken on 3.14.x through 3.15.6, from 2026-08-10. Clicking Install from an MCP server page does not add the server; the deeplink triggers but the install card never renders in the Customize MCPs pane. Fixed in 3.15.12+, available in Cursor nightly as of 2026-08-11 and not yet shipped in the stable release. Workaround: add the MCP server manually in Settings > MCP. Forum thread
Recent fixes
| Release | Change |
|---|---|
| Claude 2.1.219 2026-07-24 | claude mcp list and /mcp show the HTTP status and error text when a server fails to connect |
| Codex rust-v0.145.0 2026-07-21 | Serializes OAuth credential refreshes, enforces startup timeouts, and lets servers opt out of tool catalog caching |
| Claude 2.1.217 2026-07-21 | Fixed corporate mTLS, TLS-verify, OAuth scope, and proxy settings being ignored in Claude Desktop sessions |
| Claude 2.1.216 2026-07-20 | Fixed re-authenticate revoking working credentials before the new sign-in succeeds |
| Claude 2.1.212 2026-07-16 | Tool calls running longer than 2 minutes move to the background automatically |
| Claude 2.1.211 2026-07-15 | Fixed plugin servers not reconnecting after an idle web session woke |
| Claude 2.1.206 2026-07-09 | Fixed manual re-authentication after a single failed token refresh, and a per-server request_timeout_ms being ignored |
| Codex rust-v0.144.0 2026-07-09 | Interactive re-authentication on a mid-session 401, and serialized shared credential stores |
| Codex rust-v0.143.0 2026-07-08 | Tool search on by default, Cloudflare affinity cookies persisted, and managed MCP server matchers |
| Cursor 3.10 2026-06-30 | Admins configure Team MCP servers once and distribute them across cloud agents, the IDE, and the CLI |
| Claude 2.1.191 2026-06-24 | Discovery, token, and capability requests retry after transient network errors |
| Codex rust-v0.142.0 2026-06-22 | Added RFC 9728 protected resource OAuth discovery |
| Cursor 3.7 2026-06-17 | Resolved the remaining MCP OAuth reliability bugs |
| Codex rust-v0.140.0 2026-06-15 | MCP OAuth credentials move to encrypted local secret storage |
Client versions
Fixes are gated on the client version. Claude Code reports it with claude --version, Codex with codex --version, and Cursor in its About panel.