diff --git a/containers/api-proxy/server.js b/containers/api-proxy/server.js
index e4a2edc0..84889129 100644
--- a/containers/api-proxy/server.js
+++ b/containers/api-proxy/server.js
@@ -46,6 +46,7 @@ const STRIPPED_HEADERS = new Set([
   'authorization',
   'proxy-authorization',
   'x-api-key',
+  'x-goog-api-key',
   'forwarded',
   'via',
 ]);
@@ -167,6 +168,32 @@ function buildUpstreamPath(reqUrl, targetHost, basePath) {
   return prefix + targetUrl.pathname + targetUrl.search;
 }
 
+/**
+ * Strip the `key` query parameter from a Gemini request URL.
+ *
+ * The @google/genai SDK (and older Gemini SDK versions) may append `?key=<value>`
+ * to every request URL in addition to setting the `x-goog-api-key` header.
+ * The proxy injects the real key via the header, so the placeholder `key=`
+ * value must be removed before forwarding to Google to prevent
+ * API_KEY_INVALID errors.
+ *
+ * @param {string} reqUrl - The incoming request URL (must start with exactly one '/')
+ * @returns {string} URL with the `key` query parameter removed
+ */
+function stripGeminiKeyParam(reqUrl) {
+  // Only operate on relative request paths that begin with exactly one slash.
+  // Returning other inputs unchanged lets proxyRequest's relative-URL check reject them.
+  // The guard prevents absolute URLs (e.g. 'http://evil.com/path?key=…') and
+  // protocol-relative URLs ('//host/path') from being normalized into a relative path.
+  if (typeof reqUrl !== 'string' || !reqUrl.startsWith('/') || reqUrl.startsWith('//')) {
+    return reqUrl;
+  }
+  const parsed = new URL(reqUrl, 'http://localhost');
+  parsed.searchParams.delete('key');
+  // Reconstruct relative path only — never emit the scheme/host from the dummy base.
+  return parsed.pathname + parsed.search;
+}
+
 // Optional base path prefixes for API targets (e.g. /serving-endpoints for Databricks)
 const OPENAI_API_BASE_PATH = normalizeBasePath(process.env.OPENAI_API_BASE_PATH);
 const ANTHROPIC_API_BASE_PATH = normalizeBasePath(process.env.ANTHROPIC_API_BASE_PATH);
@@ -485,7 +512,8 @@ function proxyRequest(req, res, targetHost, injectHeaders, provider, basePath =
     Object.assign(headers, injectHeaders);
 
     // Log auth header injection for debugging credential-isolation issues
-    const injectedKey = injectHeaders['x-api-key'] || injectHeaders['authorization'];
+    // Use case-insensitive lookup since providers use mixed casing (e.g. 'Authorization' vs 'authorization')
+    const injectedKey = Object.entries(injectHeaders).find(([k]) => ['x-api-key', 'authorization', 'x-goog-api-key'].includes(k.toLowerCase()))?.[1];
     if (injectedKey) {
       const keyPreview = injectedKey.length > 8
         ? `${injectedKey.substring(0, 8)}...${injectedKey.substring(injectedKey.length - 4)}`
@@ -1016,12 +1044,18 @@ if (require.main === module) {
       const contentLength = parseInt(req.headers['content-length'], 10) || 0;
       if (checkRateLimit(req, res, 'gemini', contentLength)) return;
 
+      // Strip any ?key= query parameter — the @google/genai SDK may append it to the URL.
+      // The proxy injects the real key via x-goog-api-key header instead.
+      req.url = stripGeminiKeyParam(req.url);
+
       proxyRequest(req, res, GEMINI_API_TARGET, {
         'x-goog-api-key': GEMINI_API_KEY,
       }, 'gemini', GEMINI_API_BASE_PATH);
     });
 
     geminiServer.on('upgrade', (req, socket, head) => {
+      // Strip any ?key= query parameter — the @google/genai SDK may append it to the URL.
+      req.url = stripGeminiKeyParam(req.url);
       proxyWebSocket(req, socket, head, GEMINI_API_TARGET, {
         'x-goog-api-key': GEMINI_API_KEY,
       }, 'gemini', GEMINI_API_BASE_PATH);
@@ -1155,4 +1189,4 @@ if (require.main === module) {
 }
 
 // Export for testing
-module.exports = { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute };
+module.exports = { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute, shouldStripHeader, stripGeminiKeyParam };
diff --git a/containers/api-proxy/server.test.js b/containers/api-proxy/server.test.js
index c1ba1a46..a83617a4 100644
--- a/containers/api-proxy/server.test.js
+++ b/containers/api-proxy/server.test.js
@@ -5,7 +5,7 @@
 const http = require('http');
 const tls = require('tls');
 const { EventEmitter } = require('events');
-const { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute } = require('./server');
+const { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute, shouldStripHeader, stripGeminiKeyParam } = require('./server');
 
 describe('normalizeApiTarget', () => {
   it('should strip https:// prefix', () => {
@@ -449,6 +449,72 @@ describe('buildUpstreamPath', () => {
   });
 });
 
+describe('shouldStripHeader', () => {
+  it('should strip authorization header', () => {
+    expect(shouldStripHeader('authorization')).toBe(true);
+    expect(shouldStripHeader('Authorization')).toBe(true);
+  });
+
+  it('should strip x-api-key header', () => {
+    expect(shouldStripHeader('x-api-key')).toBe(true);
+    expect(shouldStripHeader('X-Api-Key')).toBe(true);
+  });
+
+  it('should strip x-goog-api-key header (Gemini placeholder must be stripped)', () => {
+    expect(shouldStripHeader('x-goog-api-key')).toBe(true);
+    expect(shouldStripHeader('X-Goog-Api-Key')).toBe(true);
+  });
+
+  it('should strip proxy-authorization header', () => {
+    expect(shouldStripHeader('proxy-authorization')).toBe(true);
+  });
+
+  it('should strip x-forwarded-* headers', () => {
+    expect(shouldStripHeader('x-forwarded-for')).toBe(true);
+    expect(shouldStripHeader('x-forwarded-host')).toBe(true);
+  });
+
+  it('should not strip content-type header', () => {
+    expect(shouldStripHeader('content-type')).toBe(false);
+  });
+
+  it('should not strip anthropic-version header', () => {
+    expect(shouldStripHeader('anthropic-version')).toBe(false);
+  });
+});
+
+describe('stripGeminiKeyParam', () => {
+  it('should remove the key= query parameter', () => {
+    expect(stripGeminiKeyParam('/v1/models/gemini-pro:generateContent?key=placeholder'))
+      .toBe('/v1/models/gemini-pro:generateContent');
+  });
+
+  it('should remove key= while preserving other query parameters', () => {
+    expect(stripGeminiKeyParam('/v1/models/gemini-pro:generateContent?key=placeholder&alt=json'))
+      .toBe('/v1/models/gemini-pro:generateContent?alt=json');
+  });
+
+  it('should return path unchanged when no key= parameter is present', () => {
+    expect(stripGeminiKeyParam('/v1/models/gemini-pro:generateContent'))
+      .toBe('/v1/models/gemini-pro:generateContent');
+  });
+
+  it('should return path unchanged when only unrelated query parameters exist', () => {
+    expect(stripGeminiKeyParam('/v1/models/gemini-pro:generateContent?alt=json&stream=true'))
+      .toBe('/v1/models/gemini-pro:generateContent?alt=json&stream=true');
+  });
+
+  it('should handle root path without key param', () => {
+    expect(stripGeminiKeyParam('/')).toBe('/');
+  });
+
+  it('should handle path with only key= param, leaving no trailing ?', () => {
+    // URL.search returns '' when no params remain after deletion
+    const result = stripGeminiKeyParam('/v1/generateContent?key=abc');
+    expect(result).toBe('/v1/generateContent');
+  });
+});
+
 // ── Helpers for proxyWebSocket tests ──────────────────────────────────────────
 
 /** Create a minimal mock socket with write/destroy spies. */