Claude Code tool calls hang on a non-Anthropic endpoint

Fix, plugin and write-up for Claude Code tool calls that freeze when ANTHROPIC_BASE_URL points somewhere other than api.anthropic.com — DeepSeek, OpenRouter, Groq, LiteLLM, a Bedrock/Vertex gateway, or any proxy.

If your tool calls stall, the agent says it's working, nothing appears on screen, and you end up pressing Esc to get unstuck — this is for you.

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The fix

Open ~/.claude/settings.json (%USERPROFILE%\.claude\settings.json on Windows) and add:

"env": {
  "CLAUDE_CODE_AUTO_MODE_SERVER": "0"
}

If an env block already exists, add just that one line inside it. Restart Claude Code — the setting is read at startup.

Classifier requests then bill as before, which a notice you may have seen already told you.

Or have Claude Code do it

Paste this into Claude Code:

Diagnose and fix the third-party-endpoint tool-call hang on this machine.

1. Read ~/.claude/settings.json. Report the ANTHROPIC_BASE_URL and the env block.
2. If ANTHROPIC_BASE_URL's host is not api.anthropic.com, and
   env.CLAUDE_CODE_AUTO_MODE_SERVER is missing or not "0":
     - back up settings.json first
     - add "CLAUDE_CODE_AUTO_MODE_SERVER": "0" to the env block
     - preserve every other setting exactly as it was
3. Confirm the change by re-reading the file, then tell me to restart Claude Code.

Or run the script

fix-endpoint-hang.ps1 does the same thing on Windows, with a backup and a dry run:

powershell -File fix-endpoint-hang.ps1          # dry run, changes nothing
powershell -File fix-endpoint-hang.ps1 -Apply   # writes it

It checks your endpoint first and stays out of the way if the fix doesn't apply. If settings.json is malformed it refuses to touch it rather than risk your config.

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Why this happens

Claude Code's auto mode puts a permission classifier in front of tool calls. The changelog shows that classifier moving to Anthropic's servers:

Version	Change
2.1.278	Auto mode defaults to the server-side classifier — "does not charge for classifier overhead", and it "warns on billed fallback"
2.1.281	"where its classifier review runs server-side, read-only and sandboxed shell commands also wait for that review"
2.1.282	Server-side default extended to a direct Anthropic API connection
2.1.283+	Interactive sessions on third-party providers start in auto mode by default

Tool calls wait on that review. A third-party endpoint can't serve it, so the review never returns — the call waits forever. That is the freeze.

2.1.277 predates all of it, which is why downgrading appears to fix the problem. The downgrade isn't repairing a regression, it's removing the server-side default. CLAUDE_CODE_AUTO_MODE_SERVER=0 gets the same local classifier without downgrading.

The notice you may have seen

We're changing auto mode to no longer charge for classifier requests in Claude Code. However, this session isn't eligible because your requests go through <your host>, which isn't compatible with this update. Nothing breaks: auto mode keeps working, and its classifier requests are billed as before.

Same feature, seen from the billing side. It reads like a billing problem and says "nothing breaks", which is why it sends people down the wrong path.

Why your logs look clean

A call that never returns never writes an error. Transcript scanners report "0 malformed calls, 0 errors" while the freeze happens on every call. A clean log is not evidence the problem isn't real — if something tells you it's fine because nothing shows up, that reasoning is backwards.

Also worth knowing

• WebSearch may hang too — it's Anthropic-hosted, so a third-party endpoint can't serve it either. Prefer WebFetch on a specific URL, or an MCP search server.
• A version pin can silently fail. One machine here had a recorded-successful downgrade to 2.1.277 while the running binary was still 2.1.284. Verify via the live process path and its file version, not via the config.
• permissions.defaultMode is the alternative escape — set it and sessions never enter auto mode at all.

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Install as a plugin

/plugin marketplace add RichardRamirez123/NonAnthropicEndpointFix
/plugin install third-party-endpoint-doctor@non-anthropic-endpoint-fix

Then run /endpoint-doctor. It checks your endpoint, whether the classifier is pinned, whether sessions start in auto mode, which build is actually running, and whether transcripts corroborate a stall — then offers the fix and applies it only with your confirmation.

The bundled skill also triggers on its own, so you can just say "my tool calls keep freezing".

See third-party-endpoint-doctor/ for the plugin source.

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Confidence — read this

The fix is well-supported — it's a documented configuration flag and it resolves the symptom in practice.

The mechanism is inferred, from changelog entries plus correlation, and has not been reproduced under controlled conditions. No transcript shows a call waiting on a classifier review, because a hang can't leave that trace — which is exactly why this problem is so hard to confirm from logs.

The decisive test is to remove the setting and confirm the freeze returns. Until that's recorded, treat the causal chain as strongly suggested rather than proven.

The longer write-up lives in deepseek-claude-code-fix.md. The raw investigation notes — and the transcript-scanning script used to test the claims above — are in version-test/.

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License

MIT — see LICENSE.