diff --git a/CHANGELOG.md b/CHANGELOG.md
index df662b9b..0cca4ec6 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -21,6 +21,7 @@
 
 ### Fixed
 
+- Claude Code 2.1.84 计费头 strip 行为新增 rotation 变体回归覆盖：实测 Claude Code 把 `x-anthropic-billing-header: cc_version=...; cc_entrypoint=cli; cch=<5hex>;` 作为 `system[0]` 独立块下发，`cc_version` 后缀和 `cch` 每请求 reroll；新增 `it.each` 覆盖 5 个真实 `cc_version` 后缀（c8e / 76b / f51 / 5b4 / 4f3）与"两次不同 cch 产出同一份 `instructions`"的不变性断言，防止后续改 strip（如改 `startsWith` → 正则、或加 inline 清洗）意外让 `cch` 漏进 `instructions` 污染上游 prompt cache（`tests/unit/translation/anthropic-to-codex.test.ts`）
 - Dashboard Errors tab now has a real clear action: `DELETE /admin/error-logs` removes current + backup JSONL files and the read cursor so repeated `StreamUpstreamPrematureClose` groups can be cleared from the page instead of only marked read. Anthropic setup defaults now map Opus 4.7 → `gpt-5.5` and Sonnet 4.6 → `gpt-5.4`, and the built-in Anthropic API-key catalog lists Claude Opus 4.7 (`src/logs/error-log.ts`, `src/routes/admin/error-logs.ts`, `shared/hooks/use-error-logs.ts`, `web/src/pages/ErrorsPage.tsx`, `web/src/components/AnthropicSetup.tsx`, `src/auth/api-key-catalog.ts`).
 - Claude Code 的 `Read` 工具参数里如果 `pages` 传成空字符串或空白字符串，会在 Codex → Anthropic 转换时被自动剔除，避免 GPT-5.5 反复触发 `Read tool validation error: Invalid pages parameter: ""` 并重试隔离工作树；对应单测覆盖流式与非流式两条路径，以及非空 PDF 页码范围保留（`src/translation/codex-to-anthropic.ts`、`tests/unit/translation/codex-to-anthropic-read-pages.test.ts`）。
 - Dashboard egress log details now include Codex request `reasoning` and optional `service_tier`, so `/admin/logs` can show the actual reasoning effort sent upstream instead of only `model` / `stream` / `useWebSocket` (`src/routes/shared/proxy-egress-log.ts`, `tests/unit/routes/shared/proxy-egress-log.test.ts`).
diff --git a/tests/unit/translation/anthropic-to-codex.test.ts b/tests/unit/translation/anthropic-to-codex.test.ts
index bf94d380..1aeb1a1e 100644
--- a/tests/unit/translation/anthropic-to-codex.test.ts
+++ b/tests/unit/translation/anthropic-to-codex.test.ts
@@ -106,6 +106,66 @@ describe("translateAnthropicToCodexRequest", () => {
       expect(result.instructions).toBe("Keep answers short.");
     });
 
+    // Real Claude Code 2.1.84 emits the billing header as a standalone block[0]
+    // with per-request rotating cc_version + cch. Tests must prove the strip is
+    // invariant across that rotation, otherwise the cache-buster leaks into
+    // `instructions` and tanks upstream prompt cache.
+    it.each([
+      "x-anthropic-billing-header: cc_version=2.1.84.c8e; cc_entrypoint=cli; cch=da09b;",
+      "x-anthropic-billing-header: cc_version=2.1.84.76b; cc_entrypoint=cli; cch=46d1d;",
+      "x-anthropic-billing-header: cc_version=2.1.84.f51; cc_entrypoint=cli; cch=3c1ed;",
+      "x-anthropic-billing-header: cc_version=2.1.84.5b4; cc_entrypoint=cli; cch=8f29c;",
+      "x-anthropic-billing-header: cc_version=2.1.84.4f3; cc_entrypoint=cli; cch=d1658;",
+    ])("strips Claude Code billing header variant: %s", (billingText) => {
+      const result = translateAnthropicToCodexRequest(
+        makeRequest({
+          system: [
+            { type: "text" as const, text: billingText },
+            {
+              type: "text" as const,
+              text: "You are Claude Code, Anthropic's official CLI for Claude.",
+              cache_control: { type: "ephemeral" },
+            },
+            {
+              type: "text" as const,
+              text: "\nYou are an interactive agent that helps users with software engineering tasks.",
+              cache_control: { type: "ephemeral" },
+            },
+          ],
+        }),
+      );
+      expect(result.instructions).toBe(
+        "You are Claude Code, Anthropic's official CLI for Claude.\n\nYou are an interactive agent that helps users with software engineering tasks.",
+      );
+      expect(result.instructions).not.toMatch(/cch=|cc_version=|x-anthropic-billing/);
+    });
+
+    it("produces identical instructions across rotating cc_version + cch values", () => {
+      const baseSystem = (billingText: string) => [
+        { type: "text" as const, text: billingText },
+        {
+          type: "text" as const,
+          text: "You are Claude Code, Anthropic's official CLI for Claude.",
+          cache_control: { type: "ephemeral" as const },
+        },
+      ];
+      const a = translateAnthropicToCodexRequest(
+        makeRequest({
+          system: baseSystem(
+            "x-anthropic-billing-header: cc_version=2.1.84.c8e; cc_entrypoint=cli; cch=da09b;",
+          ),
+        }),
+      );
+      const b = translateAnthropicToCodexRequest(
+        makeRequest({
+          system: baseSystem(
+            "x-anthropic-billing-header: cc_version=2.1.84.4f3; cc_entrypoint=cli; cch=d1658;",
+          ),
+        }),
+      );
+      expect(a.instructions).toBe(b.instructions);
+    });
+
     it("falls back to default instructions when no system provided", () => {
       const result = translateAnthropicToCodexRequest(makeRequest());
       expect(result.instructions).toBe("You are a helpful assistant.");