diff --git a/changelog.d/fixes/9064-fix-anthropic-code-execution-skills-beta.plan.md b/changelog.d/fixes/9064-fix-anthropic-code-execution-skills-beta.plan.md
new file mode 100644
index 0000000000..3c81c75460
--- /dev/null
+++ b/changelog.d/fixes/9064-fix-anthropic-code-execution-skills-beta.plan.md
@@ -0,0 +1 @@
+- fix(providers): anthropic strips code-execution/skills beta flag, causing container rejection (#9064)
\ No newline at end of file
diff --git a/open-sse/config/anthropicHeaders.ts b/open-sse/config/anthropicHeaders.ts
index 6a98e4aa98..2edc489d1e 100644
--- a/open-sse/config/anthropicHeaders.ts
+++ b/open-sse/config/anthropicHeaders.ts
@@ -24,6 +24,8 @@ const ANTHROPIC_BETA_BASE = Object.freeze([
   "advisor-tool-2026-03-01",
   "extended-cache-ttl-2025-04-11",
   "cache-diagnosis-2026-04-07",
+  "code-execution-2025-08-25",
+  "skills-2025-10-02",
 ]);
 
 const CLAUDE_OAUTH_EXTRA_BETAS = Object.freeze(["fine-grained-tool-streaming-2025-05-14"]);
@@ -53,6 +55,8 @@ export const ANTHROPIC_BETA_CLAUDE_OAUTH = [
 export const FORWARDABLE_CLIENT_BETAS = Object.freeze([
   "tool-search-tool-2025-10-19",
   "context-1m-2025-08-07",
+  "code-execution-2025-08-25",
+  "skills-2025-10-02",
 ]);
 
 /**
diff --git a/tests/unit/probe-9064-code-execution-beta.test.ts b/tests/unit/probe-9064-code-execution-beta.test.ts
new file mode 100644
index 0000000000..153ec53386
--- /dev/null
+++ b/tests/unit/probe-9064-code-execution-beta.test.ts
@@ -0,0 +1,68 @@
+/**
+ * TDD regression for #9064: `anthropic` provider strips code-execution and
+ * skills beta flags, so upstream rejects `container` dict form ("must be a
+ * string").
+ *
+ * Root cause: ANTHROPIC_BETA_BASE lacks `code-execution-2025-08-25` and
+ * `skills-2025-10-02`, and FORWARDABLE_CLIENT_BETAS (only 2 entries) drops
+ * any client-negotiated beta for these flags. Without them, Anthropic evaluates
+ * `container` under the old string-only contract and 400s.
+ *
+ * Fix: add both flags to FORWARDABLE_CLIENT_BETAS (forwarding only when the
+ * client explicitly requests them) and to ANTHROPIC_BETA_BASE (so raw-curl
+ * clients without an anthropic-beta header also work on the API-key path).
+ */
+import test from "node:test";
+import assert from "node:assert/strict";
+
+const { ANTHROPIC_BETA_API_KEY, mergeClientAnthropicBeta, FORWARDABLE_CLIENT_BETAS } =
+  await import("../../open-sse/config/anthropicHeaders.ts");
+
+const CODE_EXECUTION = "code-execution-2025-08-25";
+const SKILLS = "skills-2025-10-02";
+
+// ── static header assertion ─────────────────────────────────────────────────
+
+test("#9064 static ANTHROPIC_BETA_API_KEY must include code-execution beta", () => {
+  const tokens = ANTHROPIC_BETA_API_KEY.split(",").map((s) => s.trim());
+  assert.ok(
+    tokens.includes(CODE_EXECUTION),
+    `code-execution beta missing from ANTHROPIC_BETA_API_KEY: ${ANTHROPIC_BETA_API_KEY}`
+  );
+});
+
+test("#9064 static ANTHROPIC_BETA_API_KEY must include skills beta", () => {
+  const tokens = ANTHROPIC_BETA_API_KEY.split(",").map((s) => s.trim());
+  assert.ok(
+    tokens.includes(SKILLS),
+    `skills beta missing from ANTHROPIC_BETA_API_KEY: ${ANTHROPIC_BETA_API_KEY}`
+  );
+});
+
+// ── client-negotiated beta forwarding ───────────────────────────────────────
+
+test("#9064 mergeClientAnthropicBeta must forward client-negotiated code-execution beta", () => {
+  const out = mergeClientAnthropicBeta(
+    ANTHROPIC_BETA_API_KEY,
+    `claude-code-20250219,${CODE_EXECUTION}`
+  );
+  const tokens = out.split(",").map((s) => s.trim());
+  assert.ok(
+    tokens.includes(CODE_EXECUTION),
+    `client code-execution beta dropped: ${out}`
+  );
+  assert.ok(FORWARDABLE_CLIENT_BETAS.includes(CODE_EXECUTION));
+});
+
+test("#9064 mergeClientAnthropicBeta must forward client-negotiated skills beta", () => {
+  const out = mergeClientAnthropicBeta(
+    ANTHROPIC_BETA_API_KEY,
+    `claude-code-20250219,${SKILLS}`
+  );
+  const tokens = out.split(",").map((s) => s.trim());
+  assert.ok(
+    tokens.includes(SKILLS),
+    `client skills beta dropped: ${out}`
+  );
+  assert.ok(FORWARDABLE_CLIENT_BETAS.includes(SKILLS));
+});
\ No newline at end of file