Connect Claude Code to an LLM gateway changedllm-gateway-connect
Nearest release: v2.1.299, published 20 hours after upstream edited the page. Shown because the two are within 24 hours of each other. Nothing here says the release caused the edit.
Upstream edited this page at 13 Oct 2026 04:17 UTC, give or take a minute or two: the time comes from Anthropic’s own sitemap rather than from a commit. This site recorded the change at 13 Oct 2026 04:37 UTC.
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532532| `Connection refused — a firewall or proxy may be blocking it (ConnectionRefused)` when nothing answers at the address, or `Can't reach the API server — check your internet or DNS (ENOTFOUND)` when the hostname doesn't resolve, often after a silent pause while Claude Code [retries with backoff](/docs/en/errors#automatic-retries). The code in parentheses varies; [Unable to connect to API](/docs/en/errors#unable-to-connect-to-api) covers the code spellings and the earlier wording | Nothing answered at the base URL: the address is wrong, or a VPN or firewall blocks the path to the gateway | Run the [curl test above](#verify-the-connection), which fails immediately with the same cause, and confirm the URL and network path with your gateway team |
533533| `API returned an empty or malformed response (HTTP 200)` | The gateway or an intermediate proxy returned a non-API response, often an HTML error or login page | Test with the [curl request above](#verify-the-connection); fix the gateway route that answers with something other than a Claude API response. [The error reference](/docs/en/errors#api-returned-an-empty-or-malformed-response) explains the detail the message reports |
534534| `400` errors naming `context_management`, `Extra inputs are not permitted`, or other unrecognized fields | The gateway forwards requests to an upstream that rejects fields Claude Code sends to Anthropic-format endpoints | Set `CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS=1`, which suppresses most pre-release fields; see [feature pass-through](/docs/en/llm-gateway-protocol#feature-pass-through). Some betas aren't gated by this flag; for those, set the matching `CLAUDE_CODE_USE_*` provider variable so Claude Code sends only what that provider accepts |
535| `400` errors naming `thinking` or `adaptive`, such as `Input tag 'adaptive' found` | The upstream model build doesn't accept adaptive reasoning, which Claude Code requests for Claude 4.6 and later models | Upgrade the gateway's upstream. On Opus 4.6 and Sonnet 4.6, `CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING=1` works instead. The [model configuration](/docs/en/model-config) capability variables apply only to the provider configurations, such as `CLAUDE_CODE_USE_BEDROCK` and `CLAUDE_CODE_USE_VERTEX`, not behind an `ANTHROPIC_BASE_URL` gateway |
535| `400` errors naming `thinking` or `adaptive`, such as `Input tag 'adaptive' found` | The upstream model build doesn't accept adaptive reasoning, which Claude Code requests for Claude Opus 4.6, Claude Sonnet 4.6, Claude Haiku 5.5, Claude Fable 5, and later models | Upgrade the gateway's upstream. On Opus 4.6 and Sonnet 4.6, `CLAUDE_CODE_DISABLE_ADAPTIVE_THINKING=1` works instead. The [model configuration](/docs/en/model-config) capability variables apply only to the provider configurations, such as `CLAUDE_CODE_USE_BEDROCK` and `CLAUDE_CODE_USE_VERTEX`, not behind an `ANTHROPIC_BASE_URL` gateway |
536536| `400` errors stating a context or token limit in the gateway's own words, such as `ContextWindowExceededError` or `prompt token count of N exceeds the limit of M` | The gateway enforces a smaller context than the model's native window and rewrites the upstream error, so Claude Code doesn't recognize it as a [too-long error](/docs/en/errors#prompt-is-too-long) and doesn't compact and retry automatically | Run `/compact` to recover the session. To prevent it, set `CLAUDE_CODE_AUTO_COMPACT_WINDOW` to the gateway's limit; Claude Code clamps the value to at least 100,000 tokens and at most the model's context window, so you can't match a gateway limit below 100,000, and `/compact` remains the recovery there. Also set `CLAUDE_CODE_MAX_OUTPUT_TOKENS` below the gateway model's output limit |
537537| `400` errors on every request, in the gateway's own words rejecting a tool's input schema or its `pattern`, on Claude Code v2.1.265 through v2.1.267 | In a gradual rollout on those versions, the [Artifact tool](/docs/en/artifacts#availability) schema carries a regular expression with `\p{...}` Unicode character classes. The Anthropic API accepts it, but a gateway or upstream that checks each tool schema's `pattern` with its own regex engine rejects the whole request | Update to v2.1.268 or later, which doesn't send the regular expression. On an affected version, [turn artifacts off](/docs/en/artifacts#disable-artifacts), which removes the tool and its schema from requests |
538538| `400` errors on every request, in the gateway's own words rejecting an unrecognized tool type, such as `Input tag 'advisor_20260301'`, on Claude Code v2.1.275 | In a gradual rollout on that version, requests carry an [advisor tool](/docs/en/advisor) entry even with the advisor off. The Anthropic API accepts it, but a gateway or upstream that validates tool types rejects the whole request; one that [forwards request body fields unchanged](/docs/en/llm-gateway-protocol#forward-as-open-lists) passes it through unaffected. The entry is a declaration that carries no conversation content | Update to v2.1.276 or later, which doesn't send the entry behind an `ANTHROPIC_BASE_URL` gateway unless you turn the advisor on. On v2.1.275, set [`CLAUDE_CODE_DISABLE_ADVISOR_TOOL=1`](/docs/en/env-vars), which removes the entry from requests |
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