Claude Code v2.1.154 Broke Every Third-Party Provider. Here’s What Happened.

On May 28, 2026, Anthropic shipped Claude Code v2.1.154. Within hours, every non-Anthropic API provider stopped working. GLM, DeepSeek, MiniMax, Kimi, Qwen, MiMo — all of them returned the same error:

API Error: 422 {"detail":[{"type":"literal_error","loc":["body","messages",1,"role"],
"msg":"Input should be 'user' or 'assistant'","input":"system",
"ctx":{"expected":"'user' or 'assistant'"}}]}

If you’re using claude-multi to run Claude Code against a 3rd-party provider, you probably hit this.

What changed

Claude Code v2.1.150 introduced a new Anthropic beta: mid-conversation-system-2026-04-07. It’s been in every version since. This beta changes how Claude Code sends system instructions to the API.

Before, Claude Code used the top-level system parameter for system prompts. Every Anthropic-compatible API supports this:

{
  "model": "claude-sonnet-4-20250514",
  "system": "You are a helpful assistant.",
  "messages": [
    {"role": "user", "content": "Hello"}
  ]
}

After the beta, Claude Code also sends system instructions as messages with role: "system" inside the messages array:

{
  "model": "claude-sonnet-4-20250514",
  "system": "You are a helpful assistant.",
  "messages": [
    {"role": "user", "content": "Hello"},
    {"role": "system", "content": "Remember: be concise"},
    {"role": "assistant", "content": "Hi! How can I help?"}
  ]
}

The beta is opt-in via the anthropic-beta header. Claude Code enables it automatically for first-party API calls (api.anthropic.com). For third-party providers, it should be disabled. But the detection logic has a gap.

Why providers reject it

The Anthropic Messages API spec allows role: "system" in the messages array when the beta header is present. Without the header, it’s not valid. Most third-party providers implement the base spec without beta features. Their validators reject any role that isn’t "user" or "assistant", and return 422.

Claude Code has a fallback — but it’s incomplete

Anthropic anticipated this. Claude Code has built-in retry logic that detects when a provider rejects the mid-conversation-system beta. When it catches the error, it removes the beta header and falls back to putting system instructions inside <system-reminder> blocks in user messages.

The detection function (minified, from the binary):

function pP8(error) {
  if (!Yy) return false;
  if (!(error instanceof APIError) || error.status !== 400) return false;
  // ... pattern matching on error message
}

error.status !== 400. The fallback only triggers on HTTP 400. Third-party providers return HTTP 422 for validation errors. The retry logic never fires.

This is the bug. The beta feature itself is fine for first-party API. The error handling checks for one specific status code when providers use a different one for the same error.

What actually happens

1. User runs claude-glm (or any claude-multi instance)
2. Claude Code detects it’s using a third-party API
3. The mid-conversation-system beta should be disabled, but the detection has edge cases
4. Claude Code sends a request with role: "system" in the messages array
5. Provider returns HTTP 422
6. Claude Code’s fallback checks error.status !== 400 — doesn’t match 422
7. Error surfaces to the user
8. Conversation is dead

If the provider had returned 400 instead of 422, the fallback would have kicked in.

How we fixed it in claude-multi

Three layers.

Layer 1: Pin the Claude Code version

We maintain a pinned Claude Code installation at ~/.claude-multi/bin/. All claude-multi instances use this instead of the global claude binary. Currently pinned to v2.1.153, the last version before the breakage.

npm install --prefix ~/.claude-multi/bin @anthropic-ai/claude-code@2.1.153

The getClaudePath() function checks this path first, before falling back to which claude.

Layer 2: Disable auto-updates

We added DISABLE_AUTOUPDATER=1 and DISABLE_UPDATES=1 to every provider template’s environment variables. Claude Code won’t auto-update to a broken version.

From src/templates.ts:

const PROVIDER_COMMON_ENV: Record<string, string> = {
  DISABLE_AUTOUPDATER: "1",
  DISABLE_UPDATES: "1",
};

These get merged into every instance’s settings.json when created via a provider template.

Layer 3: Doctor fix for existing instances

For instances created before the fix, we added a health check and repair system.

The health check detects two wrapper formats:

1. Shell format (current): exec "/path/to/claude" "$@"
2. Node.js format (legacy): spawn("/path/to/claude", ...)

Both get flagged as version issues. The fix regenerates wrappers as clean shell scripts pointing to the pinned binary.

# CLI
claude-multi doctor check   # show issues
claude-multi doctor fix     # auto-fix

# TUI
claude-multi  # press ! for health screen, then f to fix

The TUI shows a banner when version issues are detected:

⚠ 1 error, 2 warnings — press ! to review
  ⚠ Some instances use a Claude version incompatible with 3rd-party APIs. Press ! to auto-fix.

What providers should do

Return HTTP 400, not 422, for message validation errors. Claude Code’s existing fallback handles 400. This is the fastest path to compatibility without waiting for a Claude Code patch.

What Anthropic should do

Two things:

1. Broaden the status code check in the fallback logic. error.status >= 400 && error.status < 500 instead of error.status !== 400.
2. Provide an env var to disable specific betas. CLAUDE_CODE_DISABLE_MID_CONVERSATION_SYSTEM=1 would let users opt out without downgrading.

The broader issue

This is the second time in recent months that a Claude Code update has broken third-party provider compatibility. The first was a change in how model names are validated. Anthropic tests against their own API, and third-party compatibility is incidental.

If you rely on third-party providers, pin your Claude Code version and disable auto-updates.

TL;DR

• Claude Code v2.1.150+ sends role: "system" in the messages array (new beta feature)
• Third-party providers reject it with HTTP 422
• Claude Code’s fallback only handles HTTP 400
• Fix: pin to v2.1.153, disable auto-updates, run claude-multi doctor fix