diff --git a/.env.example b/.env.example
index 844cb0659a..d356c7a123 100644
--- a/.env.example
+++ b/.env.example
@@ -449,6 +449,7 @@ GEMINI_CLI_USER_AGENT=google-api-nodejs-client/9.15.1
 
 # ── Upstream fetch (provider calls) ──
 # FETCH_TIMEOUT_MS=600000            # Total request timeout (default: 600000 = 10 min)
+#                                     # Also drives anthropic-compatible-cc-* X-Stainless-Timeout.
 # FETCH_HEADERS_TIMEOUT_MS=600000    # Time to receive response headers
 # FETCH_BODY_TIMEOUT_MS=600000       # Time to receive full response body
 # FETCH_CONNECT_TIMEOUT_MS=30000     # TCP connection establishment (default: 30s)
diff --git a/README.md b/README.md
index a6d9876fa1..e4411783c1 100644
--- a/README.md
+++ b/README.md
@@ -799,6 +799,8 @@ For most deployments, you only need:
 
 Backward compatibility is preserved: existing `FETCH_TIMEOUT_MS`, `API_BRIDGE_PROXY_TIMEOUT_MS`, and other per-layer timeout vars still work and override the shared baseline.
 
+For Claude Code-compatible upstreams (`anthropic-compatible-cc-*`), OmniRoute also derives the outbound `X-Stainless-Timeout` header from the resolved fetch timeout so provider-side read timeouts stay aligned with your env configuration.
+
 Advanced overrides are available if you need finer control:
 
 | Variable                                 | Default                                    | Purpose                                                              |
diff --git a/open-sse/services/claudeCodeCompatible.ts b/open-sse/services/claudeCodeCompatible.ts
index 0294bf3199..3c5b8c3a4e 100644
--- a/open-sse/services/claudeCodeCompatible.ts
+++ b/open-sse/services/claudeCodeCompatible.ts
@@ -1,5 +1,6 @@
 import { createHash, randomUUID } from "node:crypto";
 
+import { getStainlessTimeoutSeconds } from "@/shared/utils/runtimeTimeouts";
 import { prepareClaudeRequest } from "../translator/helpers/claudeHelper.ts";
 
 export const CLAUDE_CODE_COMPATIBLE_PREFIX = "anthropic-compatible-cc-";
@@ -12,6 +13,9 @@ export const CLAUDE_CODE_COMPATIBLE_ANTHROPIC_BETA =
 export const CLAUDE_CODE_COMPATIBLE_USER_AGENT = "claude-cli/2.1.89 (external, sdk-cli)";
 export const CLAUDE_CODE_COMPATIBLE_BILLING_HEADER =
   "x-anthropic-billing-header: cc_version=2.1.89.728; cc_entrypoint=sdk-cli; cch=00000;";
+export const CLAUDE_CODE_COMPATIBLE_STAINLESS_TIMEOUT_SECONDS = getStainlessTimeoutSeconds(
+  process.env
+);
 
 type HeaderLike =
   | Headers
@@ -97,7 +101,7 @@ export function buildClaudeCodeCompatibleHeaders(
     "x-app": "cli",
     "User-Agent": CLAUDE_CODE_COMPATIBLE_USER_AGENT,
     "X-Stainless-Retry-Count": "0",
-    "X-Stainless-Timeout": "300",
+    "X-Stainless-Timeout": String(CLAUDE_CODE_COMPATIBLE_STAINLESS_TIMEOUT_SECONDS),
     "X-Stainless-Lang": "js",
     "X-Stainless-Package-Version": "0.74.0",
     "X-Stainless-OS": "MacOS",
diff --git a/src/shared/utils/runtimeTimeouts.ts b/src/shared/utils/runtimeTimeouts.ts
index 9d5e39797b..b2794a7745 100644
--- a/src/shared/utils/runtimeTimeouts.ts
+++ b/src/shared/utils/runtimeTimeouts.ts
@@ -121,6 +121,14 @@ export function getUpstreamTimeoutConfig(
   };
 }
 
+export function getStainlessTimeoutSeconds(
+  env: EnvSource = process.env,
+  logger?: TimeoutLogger
+): number {
+  const { fetchTimeoutMs } = getUpstreamTimeoutConfig(env, logger);
+  return Math.max(1, Math.ceil(fetchTimeoutMs / 1_000));
+}
+
 export function getTlsClientTimeoutConfig(
   env: EnvSource = process.env,
   logger?: TimeoutLogger
diff --git a/tests/unit/claude-code-compatible-helpers.test.mjs b/tests/unit/claude-code-compatible-helpers.test.mjs
index 29732d6bf2..ef721f28f9 100644
--- a/tests/unit/claude-code-compatible-helpers.test.mjs
+++ b/tests/unit/claude-code-compatible-helpers.test.mjs
@@ -5,6 +5,7 @@ const {
   CLAUDE_CODE_COMPATIBLE_DEFAULT_CHAT_PATH,
   CLAUDE_CODE_COMPATIBLE_DEFAULT_MODELS_PATH,
   CLAUDE_CODE_COMPATIBLE_DEFAULT_MAX_TOKENS,
+  CLAUDE_CODE_COMPATIBLE_STAINLESS_TIMEOUT_SECONDS,
   isClaudeCodeCompatibleProvider,
   stripAnthropicMessagesSuffix,
   stripClaudeCodeCompatibleEndpointSuffix,
@@ -46,6 +47,10 @@ test("buildClaudeCodeCompatibleHeaders emits stream-aware auth headers and sessi
   assert.equal(streamHeaders.Accept, "text/event-stream");
   assert.equal(streamHeaders["x-api-key"], "sk-demo");
   assert.equal(streamHeaders["X-Claude-Code-Session-Id"], "session-123");
+  assert.equal(
+    streamHeaders["X-Stainless-Timeout"],
+    String(CLAUDE_CODE_COMPATIBLE_STAINLESS_TIMEOUT_SECONDS)
+  );
   assert.equal(jsonHeaders.Accept, "application/json");
   assert.equal(jsonHeaders["X-Claude-Code-Session-Id"], undefined);
 });
diff --git a/tests/unit/runtime-timeouts.test.mjs b/tests/unit/runtime-timeouts.test.mjs
index 8a1c5e6ce7..a1db61da52 100644
--- a/tests/unit/runtime-timeouts.test.mjs
+++ b/tests/unit/runtime-timeouts.test.mjs
@@ -65,6 +65,21 @@ test("TLS client timeout defaults to FETCH_TIMEOUT_MS and can be overridden", ()
   assert.equal(overriddenConfig.timeoutMs, 720000);
 });
 
+test("stainless timeout derives from fetch timeout and rounds up to whole seconds", () => {
+  assert.equal(
+    runtimeTimeouts.getStainlessTimeoutSeconds({
+      REQUEST_TIMEOUT_MS: "1200000",
+    }),
+    1200
+  );
+  assert.equal(
+    runtimeTimeouts.getStainlessTimeoutSeconds({
+      FETCH_TIMEOUT_MS: "600001",
+    }),
+    601
+  );
+});
+
 test("API bridge timeouts align request timeout with long proxy timeout by default", () => {
   const config = runtimeTimeouts.getApiBridgeTimeoutConfig({
     API_BRIDGE_PROXY_TIMEOUT_MS: "600000",