fix(sse): dedupe case-variant Anthropic version/beta headers (#4846)

Integrated into release/v3.8.38 (leva 5)

CHANGELOG.md

@@ -18,6 +18,7 @@ _In development — bullets added per PR; finalized at release._
 - **fix(codebuddy):** only send reasoning params when the client requests reasoning. (thanks @anki1kr)
 - **fix(sse):** keep streaming for forceStream providers when a JSON client requests it. Providers marked `forceStream:true` reject `stream:false` upstream (HTTP 400); `resolveStreamFlag` now guards against this so stream-only providers keep streaming even when the client sends `Accept: application/json` or `stream:false`. (thanks @anki1kr)
 - **fix(sse):** prevent non-JSON SSE lines and duplicate `[DONE]` from breaking clients. (thanks @qianze0628)
+- **fix(sse):** dedupe case-variant Anthropic headers in the executor `buildHeaders` path — Node/undici's `fetch` merges `anthropic-version` and `Anthropic-Version` into a single `"v, v"` value that the Anthropic API rejects, so both case variants are now collapsed to one canonical lowercase header (same for `anthropic-beta`). (thanks @Delcado19)
 
 ---
 

open-sse/config/anthropicHeaders.ts

@@ -64,6 +64,49 @@ export function mergeClientAnthropicBeta(
   return baseList.join(",");
 }
 
+/**
+ * Collapse a list of comma-list header values into a deduped, trimmed token
+ * array. Empty/undefined/null entries are dropped. Used to reconcile the
+ * case-variant `anthropic-version` / `anthropic-beta` headers below.
+ */
+function uniqueCommaValues(values: Array<string | undefined | null>): string[] {
+  return [
+    ...new Set(
+      values
+        .filter((value) => value !== undefined && value !== null && value !== "")
+        .flatMap((value) => String(value).split(","))
+        .map((value) => value.trim())
+        .filter(Boolean)
+    ),
+  ];
+}
+
+/**
+ * Dedupe case-variant Anthropic headers in-place. Node/undici's fetch merges
+ * `anthropic-version` and `Anthropic-Version` into a single `"v, v"` value,
+ * which the Anthropic API rejects (#1475). Collapse both case variants down to
+ * one canonical lowercase header carrying a single value. Same for
+ * `anthropic-beta` (joined comma-list, deduped). Mutates `headers`.
+ */
+export function normalizeAnthropicHeaderVariants(headers: Record<string, string>): void {
+  const versionValues = uniqueCommaValues([
+    headers["anthropic-version"],
+    headers["Anthropic-Version"],
+  ]);
+  delete headers["Anthropic-Version"];
+  delete headers["anthropic-version"];
+  if (versionValues.length > 0) {
+    headers["anthropic-version"] = versionValues[0];
+  }
+
+  const betaValues = uniqueCommaValues([headers["anthropic-beta"], headers["Anthropic-Beta"]]);
+  delete headers["Anthropic-Beta"];
+  delete headers["anthropic-beta"];
+  if (betaValues.length > 0) {
+    headers["anthropic-beta"] = betaValues.join(",");
+  }
+}
+
 export const CLAUDE_CLI_VERSION = "2.1.187";
 export const CLAUDE_CLI_USER_AGENT = `claude-cli/${CLAUDE_CLI_VERSION} (external, cli)`;
 export const CLAUDE_CLI_STAINLESS_PACKAGE_VERSION = "0.94.0";

open-sse/executors/base.ts

@@ -1,5 +1,8 @@
 import { HTTP_STATUS, FETCH_TIMEOUT_MS } from "../config/constants.ts";
-import { mergeClientAnthropicBeta } from "../config/anthropicHeaders.ts";
+import {
+  mergeClientAnthropicBeta,
+  normalizeAnthropicHeaderVariants,
+} from "../config/anthropicHeaders.ts";
 import { applyContextEditingToBody } from "../config/contextEditing.ts";
 import { findOffendingField, stripGroqUnsupportedFields } from "../config/providerFieldStrips.ts";
 import { applyFingerprint, isCliCompatEnabled } from "../config/cliFingerprints.ts";
@@ -576,6 +579,8 @@ export class BaseExecutor {
 
     headers["Accept"] = stream ? "text/event-stream" : "application/json";
 
+    normalizeAnthropicHeaderVariants(headers);
+
     return headers;
   }
 

open-sse/executors/default.ts

@@ -14,7 +14,10 @@ import {
 } from "../services/claudeCodeCompatible.ts";
 import { getGigachatAccessToken } from "../services/gigachatAuth.ts";
 import { getRegistryEntry } from "../config/providerRegistry.ts";
-import { mergeClientAnthropicBeta } from "../config/anthropicHeaders.ts";
+import {
+  mergeClientAnthropicBeta,
+  normalizeAnthropicHeaderVariants,
+} from "../config/anthropicHeaders.ts";
 import { applyProviderRequestDefaults } from "../services/providerRequestDefaults.ts";
 import { stripUnsupportedParams } from "../translator/paramSupport.ts";
 import {
@@ -573,6 +576,8 @@ export class DefaultExecutor extends BaseExecutor {
       }
     }
 
+    normalizeAnthropicHeaderVariants(headers);
+
     return headers;
   }
 

tests/unit/anthropic-header-dedupe-1475.test.ts

@@ -0,0 +1,67 @@
+// Regression test for #1475 — duplicate case-variant Anthropic headers.
+//
+// Node/undici's fetch lowercases and MERGES same-name headers, so an outbound
+// set carrying both "anthropic-version" and "Anthropic-Version" collapses into
+// a single "anthropic-version: 2023-06-01, 2023-06-01" value, which the
+// Anthropic API rejects. normalizeAnthropicHeaderVariants() reconciles the two
+// case variants down to one canonical lowercase header with a single value
+// (and a deduped, joined comma-list for anthropic-beta) before the request is
+// dispatched in BaseExecutor.buildHeaders / DefaultExecutor.buildHeaders.
+
+import test from "node:test";
+import assert from "node:assert/strict";
+
+import { normalizeAnthropicHeaderVariants } from "../../open-sse/config/anthropicHeaders.ts";
+import { DefaultExecutor } from "../../open-sse/executors/default.ts";
+
+test("normalizeAnthropicHeaderVariants collapses case-variant anthropic-version into one value", () => {
+  const headers: Record<string, string> = {
+    "anthropic-version": "2023-06-01",
+    "Anthropic-Version": "2023-06-01",
+  };
+
+  normalizeAnthropicHeaderVariants(headers);
+
+  // The mixed-case variant must be gone, and the lowercase one must carry a
+  // single value (no "v, v" duplication that Anthropic rejects).
+  assert.equal(headers["Anthropic-Version"], undefined);
+  assert.equal(headers["anthropic-version"], "2023-06-01");
+  assert.ok(!headers["anthropic-version"].includes(","));
+});
+
+test("normalizeAnthropicHeaderVariants dedupes and joins anthropic-beta variants", () => {
+  const headers: Record<string, string> = {
+    "anthropic-beta": "oauth-2025-04-20, prompt-caching",
+    "Anthropic-Beta": "prompt-caching, fine-grained",
+  };
+
+  normalizeAnthropicHeaderVariants(headers);
+
+  assert.equal(headers["Anthropic-Beta"], undefined);
+  assert.equal(headers["anthropic-beta"], "oauth-2025-04-20,prompt-caching,fine-grained");
+});
+
+test("normalizeAnthropicHeaderVariants leaves a single lowercase header untouched", () => {
+  const headers: Record<string, string> = { "anthropic-version": "2023-06-01" };
+  normalizeAnthropicHeaderVariants(headers);
+  assert.equal(headers["anthropic-version"], "2023-06-01");
+  assert.equal(headers["Anthropic-Version"], undefined);
+});
+
+test("normalizeAnthropicHeaderVariants is a no-op when no anthropic headers are present", () => {
+  const headers: Record<string, string> = { "Content-Type": "application/json" };
+  normalizeAnthropicHeaderVariants(headers);
+  assert.deepEqual(headers, { "Content-Type": "application/json" });
+});
+
+test("DefaultExecutor.buildHeaders does not emit duplicate anthropic-version variants for an anthropic-compatible provider", () => {
+  const executor = new DefaultExecutor("anthropic-compatible-test");
+  const headers = executor.buildHeaders({ apiKey: "sk-test" }, true) as Record<string, string>;
+
+  // Whatever case the upstream registry/auth path used, only the canonical
+  // lowercase header survives, with exactly one value.
+  assert.equal(headers["Anthropic-Version"], undefined);
+  if (headers["anthropic-version"] !== undefined) {
+    assert.ok(!headers["anthropic-version"].includes(","));
+  }
+});