diff --git a/lib/Client.php b/lib/Client.php
index 4f41443..0f332a5 100644
--- a/lib/Client.php
+++ b/lib/Client.php
@@ -688,6 +688,12 @@ public function loadFlags()
             return;
         }
 
+        $responseCode = $response->getResponseCode();
+        if ($responseCode !== 200) {
+            error_log("[PostHog][Client] Failed to load feature flags (HTTP $responseCode): " . $response->getResponse());
+            return;
+        }
+
         $payload = json_decode($response->getResponse(), true);
 
         if ($payload && array_key_exists("detail", $payload)) {
@@ -724,7 +730,7 @@ public function localFlags(): HttpResponse
         }
 
         return $this->httpClient->sendRequest(
-            '/api/feature_flag/local_evaluation?send_cohorts&token=' . $this->apiKey,
+            '/flags/definitions?send_cohorts&token=' . $this->apiKey,
             null,
             $headers,
             [
diff --git a/test/EtagSupportTest.php b/test/EtagSupportTest.php
index eeb3aec..b9878ab 100644
--- a/test/EtagSupportTest.php
+++ b/test/EtagSupportTest.php
@@ -285,9 +285,8 @@ public function testUpdatesEtagWhen304ResponseIncludesNewEtag(): void
 
     public function testProcessesErrorResponseWithoutFlagsKey(): void
     {
-        // This test verifies current behavior: error responses without a 'flags' key
-        // will result in empty flags (due to $payload['flags'] ?? [])
-        // This is pre-existing behavior that's consistent with or without ETag support
+        // Server error responses (non-200) log and return gracefully,
+        // preserving previously loaded flags.
 
         $this->http_client = new MockedHttpClient(
             host: "app.posthog.com",
@@ -311,15 +310,9 @@ public function testProcessesErrorResponseWithoutFlagsKey(): void
             ['response' => ['error' => 'Internal Server Error'], 'etag' => null, 'responseCode' => 500]
         ]);
 
-        // loadFlags will parse the response and set featureFlags to []
-        // This is pre-existing behavior: error responses clear flags
+        // loadFlags logs the error and returns — flags are preserved from the first load
         $this->client->loadFlags();
-
-        // Flags are cleared because response doesn't have 'flags' key
-        // ($payload['flags'] ?? [] evaluates to [])
-        $this->assertCount(0, $this->client->featureFlags);
-
-        // ETag is set to null (from the response)
-        $this->assertNull($this->client->getFlagsEtag());
+        $this->assertCount(1, $this->client->featureFlags);
+        $this->assertEquals('person-flag', $this->client->featureFlags[0]['key']);
     }
 }
diff --git a/test/FeatureFlagLocalEvaluationTest.php b/test/FeatureFlagLocalEvaluationTest.php
index 66580fc..13cc28a 100644
--- a/test/FeatureFlagLocalEvaluationTest.php
+++ b/test/FeatureFlagLocalEvaluationTest.php
@@ -1081,7 +1081,7 @@ public function testFlagPersonBooleanProperties()
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -1325,20 +1325,25 @@ public function testLoadFeatureFlags()
 
     public function testLoadFeatureFlagsWrongKey()
     {
-        self::expectException(Exception::class);
+        // Non-200 responses log and return gracefully (no exception).
+        // Flags remain empty.
         $this->http_client = new MockedHttpClient(
             host: "app.posthog.com",
-            flagEndpointResponse: ["detail" => "Invalid personal API key."]
+            flagEndpointResponse: ["detail" => "Invalid personal API key."],
+            flagEndpointResponseCode: 401
         );
         $this->client = new Client(
             self::FAKE_API_KEY,
             [
                 "debug" => true,
+                "host" => "localhost:39876",
             ],
             $this->http_client,
             self::FAKE_API_KEY
         );
         PostHog::init(null, null, $this->client);
+
+        $this->assertEmpty($this->client->featureFlags);
     }
 
     public function testSimpleFlag()
@@ -1364,7 +1369,7 @@ public function testSimpleFlag()
                 $this->http_client->calls,
                 array(
                     0 => array(
-                        "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                        "path" => "/flags/definitions?send_cohorts&token=random_key",
                         "payload" => null,
                         "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                         "requestOptions" => array("includeEtag" => true),
@@ -1462,7 +1467,7 @@ public function testComputingInactiveFlagLocally()
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -1497,7 +1502,7 @@ public function testFeatureFlagsLocalEvaluationForCohorts()
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -1568,7 +1573,7 @@ public function testFeatureFlagsLocalEvaluationForNegatedCohorts()
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
diff --git a/test/FeatureFlagTest.php b/test/FeatureFlagTest.php
index e8e433a..2ad7b10 100644
--- a/test/FeatureFlagTest.php
+++ b/test/FeatureFlagTest.php
@@ -65,7 +65,7 @@ public function testIsFeatureEnabled($response)
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -135,7 +135,7 @@ public function testIsFeatureEnabledGroups($response)
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -164,7 +164,7 @@ public function testGetFeatureFlag($response)
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -231,7 +231,7 @@ public function testGetFeatureFlagGroups($response)
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -493,9 +493,9 @@ public function testGetFeatureFlagResultWithLocalEvaluationOnly(): void
         $this->assertEquals('simple-flag', $result->getKey());
         $this->assertTrue($result->isEnabled());
 
-        // Verify no /flags/ network call was made
+        // Verify no decide (/flags/?v=2) call was made
         foreach ($this->http_client->calls as $call) {
-            $this->assertStringNotContainsString('/flags/', $call['path'], 'Expected no /flags/ call for local evaluation');
+            $this->assertFalse(str_starts_with($call['path'], '/flags/?'), 'Expected no decide call for local evaluation');
         }
     }
 
@@ -527,9 +527,9 @@ public function testGetFeatureFlagResultReturnsNullForLocalEvaluationWhenFlagCan
 
         $this->assertNull($result);
 
-        // Verify no /flags/ network call was made
+        // Verify no decide (/flags/?v=2) call was made
         foreach ($this->http_client->calls as $call) {
-            $this->assertStringNotContainsString('/flags/', $call['path'], 'Expected no /flags/ call for local evaluation only');
+            $this->assertFalse(str_starts_with($call['path'], '/flags/?'), 'Expected no decide call for local evaluation only');
         }
     }
 
@@ -554,7 +554,7 @@ public function testGetFeatureFlagResultWithGroups($response): void
         // Verify that groups were passed in the /flags/ request
         $flagsCall = null;
         foreach ($this->http_client->calls as $call) {
-            if (str_contains($call['path'], '/flags/')) {
+            if (str_starts_with($call['path'], '/flags/?')) {
                 $flagsCall = $call;
                 break;
             }
diff --git a/test/MockedHttpClient.php b/test/MockedHttpClient.php
index 28b5b7b..1d2c11f 100644
--- a/test/MockedHttpClient.php
+++ b/test/MockedHttpClient.php
@@ -75,16 +75,8 @@ public function sendRequest(string $path, ?string $payload, array $extraHeaders
         }
         array_push($this->calls, array("path" => $path, "payload" => $payload, "extraHeaders" => $extraHeaders, "requestOptions" => $requestOptions));
 
-        if (str_starts_with($path, "/flags/")) {
-            return new HttpResponse(
-                json_encode($this->flagsEndpointResponse),
-                $this->flagsEndpointResponseCode,
-                null,
-                $this->flagsEndpointCurlErrno
-            );
-        }
-
-        if (str_starts_with($path, "/api/feature_flag/local_evaluation")) {
+        // Local evaluation endpoint: /flags/definitions?...
+        if (str_starts_with($path, "/flags/definitions")) {
             // Check if we have a response queue
             if ($this->flagEndpointResponseQueue !== null && !empty($this->flagEndpointResponseQueue)) {
                 $nextResponse = array_shift($this->flagEndpointResponseQueue);
@@ -112,6 +104,16 @@ public function sendRequest(string $path, ?string $payload, array $extraHeaders
             );
         }
 
+        // Decide endpoint: /flags/?v=2
+        if (str_starts_with($path, "/flags/?")) {
+            return new HttpResponse(
+                json_encode($this->flagsEndpointResponse),
+                $this->flagsEndpointResponseCode,
+                null,
+                $this->flagsEndpointCurlErrno
+            );
+        }
+
         return parent::sendRequest($path, $payload, $extraHeaders, $requestOptions);
     }
 }
diff --git a/test/PostHogTest.php b/test/PostHogTest.php
index 44d5ce8..f2fc875 100644
--- a/test/PostHogTest.php
+++ b/test/PostHogTest.php
@@ -253,7 +253,7 @@ public function testCaptureWithSendFeatureFlagsOption(): void
                 $this->http_client->calls,
                 array (
                     0 => array (
-                        "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                        "path" => "/flags/definitions?send_cohorts&token=random_key",
                         "payload" => null,
                         "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                         "requestOptions" => array("includeEtag" => true),
@@ -309,7 +309,7 @@ public function testCaptureWithLocalSendFlags(): void
                 $this->http_client->calls,
                 array (
                     0 => array (
-                        "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                        "path" => "/flags/definitions?send_cohorts&token=random_key",
                         "payload" => null,
                         "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                         "requestOptions" => array("includeEtag" => true),
@@ -358,7 +358,7 @@ public function testCaptureWithLocalSendFlagsNoOverrides(): void
                 $this->http_client->calls,
                 array (
                     0 => array (
-                        "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                        "path" => "/flags/definitions?send_cohorts&token=random_key",
                         "payload" => null,
                         "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                         "requestOptions" => array("includeEtag" => true),
@@ -537,7 +537,7 @@ public function testDefaultPropertiesGetAddedProperly(): void
             $this->http_client->calls,
             array(
                 0 => array(
-                    "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                    "path" => "/flags/definitions?send_cohorts&token=random_key",
                     "payload" => null,
                     "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                     "requestOptions" => array("includeEtag" => true),
@@ -637,7 +637,7 @@ public function testCaptureWithSendFeatureFlagsFalse(): void
                 $this->http_client->calls,
                 array (
                     0 => array (
-                        "path" => "/api/feature_flag/local_evaluation?send_cohorts&token=random_key",
+                        "path" => "/flags/definitions?send_cohorts&token=random_key",
                         "payload" => null,
                         "extraHeaders" => array(0 => 'User-Agent: posthog-php/' . PostHog::VERSION, 1 => 'Authorization: Bearer test'),
                         "requestOptions" => array("includeEtag" => true),