From fb9fab0206aa753e104ae4620e6ddcfb7a2ea5b2 Mon Sep 17 00:00:00 2001
From: Federico Liva <fede91it@gmail.com>
Date: Sat, 5 Sep 2026 21:25:28 +0700
Subject: [PATCH] fix(anthropic-compatible): send Claude beta flags to nodes
 fronting Anthropic (#3797)

---
 open-sse/executors/default.js               | 13 ++++++-
 tests/unit/claude-header-forwarding.test.js | 40 +++++++++++++++++++++
 2 files changed, 52 insertions(+), 1 deletion(-)

diff --git a/open-sse/executors/default.js b/open-sse/executors/default.js
index 92c78e92..00f3e3de 100644
--- a/open-sse/executors/default.js
+++ b/open-sse/executors/default.js
@@ -154,7 +154,18 @@ export class DefaultExecutor extends BaseExecutor {
     for (const hook of desc.hooks || []) HEADER_HOOKS[hook]?.(headers, credentials);
     applyAuth(headers, desc, credentials);
 
-    if (this.provider === "claude" && model) {
+    // anthropic-compatible-* nodes serving a real Claude model sit in front of
+    // Anthropic itself (a rotating multi-account proxy, a corporate gateway),
+    // so the request needs the same beta flags the `claude` provider sends:
+    // without `context-management-2025-06-27` upstream rejects the
+    // `context_management` block Claude Code puts in every request with
+    // "context_management: Extra inputs are not permitted" (HTTP 400), and the
+    // combo silently falls through to the next model. The model id gates this:
+    // a node fronting Kimi or GLM answers on its own ids and never matches, so
+    // gateways that would choke on unknown beta flags are left untouched.
+    const isClaudeModel = typeof model === "string" && /^claude-/.test(model);
+    if (model && (this.provider === "claude"
+      || (this.provider?.startsWith?.("anthropic-compatible-") && isClaudeModel))) {
       headers["Anthropic-Beta"] = selectAnthropicBeta(model);
     }
 
diff --git a/tests/unit/claude-header-forwarding.test.js b/tests/unit/claude-header-forwarding.test.js
index 840a8559..d813f356 100644
--- a/tests/unit/claude-header-forwarding.test.js
+++ b/tests/unit/claude-header-forwarding.test.js
@@ -187,6 +187,46 @@ describe("DefaultExecutor.buildHeaders() — anthropic-compatible stripping", ()
       headers["Anthropic-Version"] || headers["anthropic-version"];
     expect(hasVersion).toBeDefined();
   });
+
+  // A node fronting Anthropic (rotating multi-account proxy, corporate gateway)
+  // needs the same beta flags the `claude` provider sends. Without
+  // context-management-2025-06-27 upstream answers HTTP 400
+  // "context_management: Extra inputs are not permitted" and the combo falls
+  // through to the next model without anyone noticing.
+  it("sends context-management beta for a Claude model on a custom host", () => {
+    const executor = new DefaultExecutor("anthropic-compatible-custom");
+    const headers = executor.buildHeaders(
+      {
+        apiKey: "key",
+        providerSpecificData: { baseUrl: "https://myproxy.example.com/v1" },
+      },
+      true,
+      undefined,
+      "claude-opus-5"
+    );
+
+    const betaFlags = (headers["Anthropic-Beta"] || headers["anthropic-beta"] || "")
+      .split(",").map(s => s.trim());
+    expect(betaFlags).toContain("context-management-2025-06-27");
+    // The first-party identity flag is still stripped for a non-Anthropic host.
+    expect(betaFlags).not.toContain("claude-code-20250219");
+  });
+
+  it("gates the beta flags on the model id, not the provider prefix", () => {
+    const executor = new DefaultExecutor("anthropic-compatible-custom");
+    const headers = executor.buildHeaders(
+      {
+        apiKey: "key",
+        providerSpecificData: { baseUrl: "https://myproxy.example.com/v1" },
+      },
+      true,
+      undefined,
+      "kimi-k3"
+    );
+
+    const betaVal = headers["Anthropic-Beta"] || headers["anthropic-beta"] || "";
+    expect(betaVal).not.toContain("context-management-2025-06-27");
+  });
 });
 
 // ─── proxyFetch anthropicFetch routing ────────────────────────────────────────