diff --git a/src/protocols/encoders/messages.ts b/src/protocols/encoders/messages.ts
index d41d8004306..dc9ee2e4699 100644
--- a/src/protocols/encoders/messages.ts
+++ b/src/protocols/encoders/messages.ts
@@ -27,6 +27,7 @@ import {
   anthropicUsage,
   boundedReasoningIdentity,
   collectAnthropicMessage,
+  isContextOverflowError,
   isClaudeWebSearchToolName,
   messageSnapshot,
   sanitizeWebSearchInput,
@@ -389,8 +390,9 @@ function createAnthropicMessageWriter(
       }
       const message = typeof error.message === "string" ? error.message : "upstream request failed";
       const deterministic = error.code === UNDECLARED_TOOL_CALL_ERROR_CODE;
+      const overflow = isContextOverflowError(error, message);
       fail(anthropicFailedStatus(error, message), message, !deterministic,
-        deterministic || error.code === "context_length_exceeded" ? error.code as string : undefined);
+        deterministic ? error.code as string : overflow ? "context_length_exceeded" : undefined);
     },
     overflow() {
       fail(413, "upstream translation buffer exceeded the safe limit", false, "translation_buffer_limit");
diff --git a/structure/data-planes/protocol-paths.md b/structure/data-planes/protocol-paths.md
index 4b7ed7e8599..b399fa2788b 100644
--- a/structure/data-planes/protocol-paths.md
+++ b/structure/data-planes/protocol-paths.md
@@ -223,11 +223,11 @@ the wire-silence heartbeat and live-destination stall watchdog ([timeout policy]
 `chat.ts` (`encodeChatCompletionSse`, `foldChatCompletion`) and `messages.ts`
 (`encodeAnthropicMessageSse`, `foldAnthropicMessage`) are the writers; the Chat one also emits `reasoning_details` ([#7429](chat-reasoning-details.md)). They reuse the
 converters' own helpers, exported from `src/chat/outbound.ts` and `src/claude/outbound.ts`
-(ids, chunk and frame builders, usage mapping, `chatCompletionsStreamErrorPayload`,
-`chatCompletionsFailedResponse`, `chatCompletionsIncompleteOutcome`,
-`anthropicIncompleteOutcome`, `anthropicFailedStatus`, the message snapshot, the web-search pair),
-so the frames a client receives are the converters' frames. A fold is the encoded stream read by
-the existing collector. Only producer-marked watchdog/EOF terminals retain local Chat wording; upstream copies of their reason or message follow [client error normalization](error-detail.md#client-error-bodies-chat). Explicit incomplete reasons use the [shared normalization contract](../transports/responses-wire-shapes.md#adapter-incomplete-reasons) before the writers classify the outcome.
+(ids, chunk and frame builders, usage mapping, `chatCompletionsStreamErrorPayload`, `chatCompletionsFailedResponse`, `chatCompletionsIncompleteOutcome`,
+`anthropicIncompleteOutcome`, `anthropicFailedStatus`, `isContextOverflowError`, the message snapshot, the web-search pair),
+so the frames a client receives are the converters' frames. A fold is the encoded stream read by the existing collector.
+Messages terminal errors use the shared context-overflow verdict for their code as well as their status: definite generic-coded refusals receive `context_length_exceeded` and `prompt is too long` wording even when marked retryable, while the deterministic undeclared-tool error keeps its code. `tests/responses/protocol-direct-encoders-messages.test.ts` pins stream and fold parity.
+Only producer-marked watchdog/EOF terminals retain local Chat wording; upstream copies of their reason or message follow [client error normalization](error-detail.md#client-error-bodies-chat). Explicit incomplete reasons use the [shared normalization contract](../transports/responses-wire-shapes.md#adapter-incomplete-reasons) before the writers classify the outcome.
 
 Deliberate equivalences, pinned by the parity tests: a Chat function call is delivered as one
 complete tool-call chunk when it completes, as the converter always did; Messages streams
diff --git a/tests/responses/protocol-direct-encoders-messages.test.ts b/tests/responses/protocol-direct-encoders-messages.test.ts
index 666e8f4f7cc..f0595cb0e96 100644
--- a/tests/responses/protocol-direct-encoders-messages.test.ts
+++ b/tests/responses/protocol-direct-encoders-messages.test.ts
@@ -339,6 +339,20 @@ describe("direct Messages encoder matches bridge + converter (stream)", () => {
 });
 
 describe("direct Messages fold matches bridge + collector (non-stream)", () => {
+  test.each(["server_error", "upstream_error", "api_error", "internal_error"])(
+    "generic-coded %s context overflow triggers client compaction on both paths", async code => {
+      const events: AdapterEvent[] = [{ type: "error", errorType: "server_error",
+        code, message: "Your input exceeds the context window of this model", retryable: true }];
+      const frames = await expectStreamParity(events);
+      expect(frames).toEqual([{ event: "error", data: { type: "error", error: {
+        type: "invalid_request_error", code: "context_length_exceeded",
+        message: "prompt is too long: Your input exceeds the context window of this model",
+      } } }]);
+      const response = await expectFoldParity(events);
+      expect(response.status).toBe(400);
+    },
+  );
+
   test.each([400, 413, undefined])("context rejection remains terminal with upstream status %s", async status => {
     const events: AdapterEvent[] = [{ type: "error", status, errorType: "invalid_request_error",
       code: "context_length_exceeded", message: "Synthetic input limit", retryable: false }];