diff --git a/copilot-sdk b/copilot-sdk
index ccb7d5f..a552ae4 160000
--- a/copilot-sdk
+++ b/copilot-sdk
@@ -1 +1 @@
-Subproject commit ccb7d5f386ca43cc0d6857409f0b9d35129234d9
+Subproject commit a552ae497313143e2426d6ff7e99b2632ab573dd
diff --git a/src/Client.php b/src/Client.php
index 4ee79da..d414d3e 100644
--- a/src/Client.php
+++ b/src/Client.php
@@ -235,6 +235,7 @@ public function createSession(SessionConfig|array $config = []): CopilotSession
         $response = $this->rpcClient->request('session.create', array_filter([
             'sessionId' => $config['sessionId'] ?? null,
             'model' => $config['model'] ?? null,
+            'reasoningEffort' => $config['reasoningEffort'] ?? null,
             'tools' => $toolsForRequest ?: null,
             'systemMessage' => $config['systemMessage'] ?? null,
             'availableTools' => $config['availableTools'] ?? null,
@@ -309,6 +310,7 @@ public function resumeSession(string $sessionId, ResumeSessionConfig|array $conf
 
         $response = $this->rpcClient->request('session.resume', array_filter([
             'sessionId' => $sessionId,
+            'reasoningEffort' => $config['reasoningEffort'] ?? null,
             'tools' => $toolsForRequest ?: null,
             'provider' => $config['provider'] ?? null,
             'requestPermission' => isset($config['onPermissionRequest']),
diff --git a/src/Enums/ReasoningEffort.php b/src/Enums/ReasoningEffort.php
new file mode 100644
index 0000000..aa7f93f
--- /dev/null
+++ b/src/Enums/ReasoningEffort.php
@@ -0,0 +1,19 @@
+<?php
+
+declare(strict_types=1);
+
+namespace Revolution\Copilot\Enums;
+
+/**
+ * Valid reasoning effort levels for models that support it.
+ *
+ * This controls the computational effort level that models use when generating responses.
+ * Only valid for models where capabilities.supports.reasoningEffort is true.
+ */
+enum ReasoningEffort: string
+{
+    case LOW = 'low';
+    case MEDIUM = 'medium';
+    case HIGH = 'high';
+    case XHIGH = 'xhigh';
+}
diff --git a/src/Types/ModelCapabilities.php b/src/Types/ModelCapabilities.php
index ed377e5..9ec6893 100644
--- a/src/Types/ModelCapabilities.php
+++ b/src/Types/ModelCapabilities.php
@@ -39,6 +39,14 @@ public function supportsVision(): bool
         return $this->supports['vision'] ?? false;
     }
 
+    /**
+     * Check if reasoning effort is supported.
+     */
+    public function supportsReasoningEffort(): bool
+    {
+        return $this->supports['reasoningEffort'] ?? false;
+    }
+
     /**
      * Get max context window tokens.
      */
diff --git a/src/Types/ModelInfo.php b/src/Types/ModelInfo.php
index ad2fb80..df18ba1 100644
--- a/src/Types/ModelInfo.php
+++ b/src/Types/ModelInfo.php
@@ -5,6 +5,7 @@
 namespace Revolution\Copilot\Types;
 
 use Illuminate\Contracts\Support\Arrayable;
+use Revolution\Copilot\Enums\ReasoningEffort;
 
 /**
  * Information about an available model.
@@ -22,21 +23,34 @@ public function __construct(
         public ?ModelPolicy $policy = null,
         /** Billing information */
         public ?ModelBilling $billing = null,
+        /** Supported reasoning effort levels (only present if model supports reasoning effort) */
+        public ?array $supportedReasoningEfforts = null,
+        /** Default reasoning effort level (only present if model supports reasoning effort) */
+        public ReasoningEffort|string|null $defaultReasoningEffort = null,
     ) {}
 
     /**
      * Create from array.
      *
-     * @param  array{id: string, name: string, capabilities: array, policy?: array, billing?: array}  $data
+     * @param  array{id: string, name: string, capabilities: array, policy?: array, billing?: array, supportedReasoningEfforts?: array, defaultReasoningEffort?: string}  $data
      */
     public static function fromArray(array $data): self
     {
+        $defaultReasoningEffort = null;
+        if (isset($data['defaultReasoningEffort'])) {
+            $defaultReasoningEffort = is_string($data['defaultReasoningEffort'])
+                ? $data['defaultReasoningEffort']
+                : $data['defaultReasoningEffort'];
+        }
+
         return new self(
             id: $data['id'],
             name: $data['name'],
             capabilities: ModelCapabilities::fromArray($data['capabilities']),
             policy: isset($data['policy']) ? ModelPolicy::fromArray($data['policy']) : null,
             billing: isset($data['billing']) ? ModelBilling::fromArray($data['billing']) : null,
+            supportedReasoningEfforts: $data['supportedReasoningEfforts'] ?? null,
+            defaultReasoningEffort: $defaultReasoningEffort,
         );
     }
 
@@ -45,12 +59,18 @@ public static function fromArray(array $data): self
      */
     public function toArray(): array
     {
+        $defaultReasoningEffort = $this->defaultReasoningEffort instanceof ReasoningEffort
+            ? $this->defaultReasoningEffort->value
+            : $this->defaultReasoningEffort;
+
         return array_filter([
             'id' => $this->id,
             'name' => $this->name,
             'capabilities' => $this->capabilities->toArray(),
             'policy' => $this->policy?->toArray(),
             'billing' => $this->billing?->toArray(),
+            'supportedReasoningEfforts' => $this->supportedReasoningEfforts,
+            'defaultReasoningEffort' => $defaultReasoningEffort,
         ], fn ($v) => $v !== null);
     }
 }
diff --git a/src/Types/ResumeSessionConfig.php b/src/Types/ResumeSessionConfig.php
index aec80e2..164228e 100644
--- a/src/Types/ResumeSessionConfig.php
+++ b/src/Types/ResumeSessionConfig.php
@@ -6,6 +6,7 @@
 
 use Closure;
 use Illuminate\Contracts\Support\Arrayable;
+use Revolution\Copilot\Enums\ReasoningEffort;
 
 /**
  * Configuration for resuming a session.
@@ -13,6 +14,12 @@
 readonly class ResumeSessionConfig implements Arrayable
 {
     public function __construct(
+        /**
+         * Reasoning effort level for models that support it.
+         * Only valid for models where capabilities.supports.reasoningEffort is true.
+         * Accepts either ReasoningEffort enum or string value.
+         */
+        public ReasoningEffort|string|null $reasoningEffort = null,
         /**
          * Tools exposed to the CLI server.
          */
@@ -79,6 +86,13 @@ public function __construct(
      */
     public static function fromArray(array $data): self
     {
+        $reasoningEffort = null;
+        if (isset($data['reasoningEffort'])) {
+            $reasoningEffort = $data['reasoningEffort'] instanceof ReasoningEffort
+                ? $data['reasoningEffort']
+                : $data['reasoningEffort'];
+        }
+
         $provider = null;
         if (isset($data['provider'])) {
             $provider = $data['provider'] instanceof ProviderConfig
@@ -94,6 +108,7 @@ public static function fromArray(array $data): self
         }
 
         return new self(
+            reasoningEffort: $reasoningEffort,
             tools: $data['tools'] ?? null,
             provider: $provider,
             onPermissionRequest: $data['onPermissionRequest'] ?? null,
@@ -114,6 +129,10 @@ public static function fromArray(array $data): self
      */
     public function toArray(): array
     {
+        $reasoningEffort = $this->reasoningEffort instanceof ReasoningEffort
+            ? $this->reasoningEffort->value
+            : $this->reasoningEffort;
+
         $provider = $this->provider instanceof ProviderConfig
             ? $this->provider->toArray()
             : $this->provider;
@@ -123,6 +142,7 @@ public function toArray(): array
             : $this->hooks;
 
         return array_filter([
+            'reasoningEffort' => $reasoningEffort,
             'tools' => $this->tools,
             'provider' => $provider,
             'onPermissionRequest' => $this->onPermissionRequest,
diff --git a/src/Types/SessionConfig.php b/src/Types/SessionConfig.php
index 614177b..9626a54 100644
--- a/src/Types/SessionConfig.php
+++ b/src/Types/SessionConfig.php
@@ -6,6 +6,7 @@
 
 use Closure;
 use Illuminate\Contracts\Support\Arrayable;
+use Revolution\Copilot\Enums\ReasoningEffort;
 
 /**
  * Configuration for creating a session.
@@ -22,6 +23,13 @@ public function __construct(
          * Model to use for this session.
          */
         public ?string $model = null,
+        /**
+         * Reasoning effort level for models that support it.
+         * Only valid for models where capabilities.supports.reasoningEffort is true.
+         * Use client.listModels() to check supported values for each model.
+         * Accepts either ReasoningEffort enum or string value.
+         */
+        public ReasoningEffort|string|null $reasoningEffort = null,
         /**
          * Override the default configuration directory location.
          * When specified, the session will use this directory for storing config and state.
@@ -135,9 +143,17 @@ public static function fromArray(array $data): self
                 : SessionHooks::fromArray($data['hooks']);
         }
 
+        $reasoningEffort = null;
+        if (isset($data['reasoningEffort'])) {
+            $reasoningEffort = $data['reasoningEffort'] instanceof ReasoningEffort
+                ? $data['reasoningEffort']
+                : $data['reasoningEffort'];
+        }
+
         return new self(
             sessionId: $data['sessionId'] ?? null,
             model: $data['model'] ?? null,
+            reasoningEffort: $reasoningEffort,
             configDir: $data['configDir'] ?? null,
             tools: $data['tools'] ?? null,
             systemMessage: $systemMessage,
@@ -162,6 +178,10 @@ public static function fromArray(array $data): self
      */
     public function toArray(): array
     {
+        $reasoningEffort = $this->reasoningEffort instanceof ReasoningEffort
+            ? $this->reasoningEffort->value
+            : $this->reasoningEffort;
+
         $systemMessage = $this->systemMessage instanceof SystemMessageConfig
             ? $this->systemMessage->toArray()
             : $this->systemMessage;
@@ -181,6 +201,7 @@ public function toArray(): array
         return array_filter([
             'sessionId' => $this->sessionId,
             'model' => $this->model,
+            'reasoningEffort' => $reasoningEffort,
             'configDir' => $this->configDir,
             'tools' => $this->tools,
             'systemMessage' => $systemMessage,
diff --git a/tests/Unit/Enums/ReasoningEffortTest.php b/tests/Unit/Enums/ReasoningEffortTest.php
new file mode 100644
index 0000000..a270bbf
--- /dev/null
+++ b/tests/Unit/Enums/ReasoningEffortTest.php
@@ -0,0 +1,31 @@
+<?php
+
+declare(strict_types=1);
+
+use Revolution\Copilot\Enums\ReasoningEffort;
+
+describe('ReasoningEffort', function () {
+    it('has correct string values', function () {
+        expect(ReasoningEffort::LOW->value)->toBe('low')
+            ->and(ReasoningEffort::MEDIUM->value)->toBe('medium')
+            ->and(ReasoningEffort::HIGH->value)->toBe('high')
+            ->and(ReasoningEffort::XHIGH->value)->toBe('xhigh');
+    });
+
+    it('can be created from string', function () {
+        expect(ReasoningEffort::from('low'))->toBe(ReasoningEffort::LOW)
+            ->and(ReasoningEffort::from('medium'))->toBe(ReasoningEffort::MEDIUM)
+            ->and(ReasoningEffort::from('high'))->toBe(ReasoningEffort::HIGH)
+            ->and(ReasoningEffort::from('xhigh'))->toBe(ReasoningEffort::XHIGH);
+    });
+
+    it('has all expected cases', function () {
+        $cases = ReasoningEffort::cases();
+
+        expect($cases)->toHaveCount(4)
+            ->and($cases)->toContain(ReasoningEffort::LOW)
+            ->and($cases)->toContain(ReasoningEffort::MEDIUM)
+            ->and($cases)->toContain(ReasoningEffort::HIGH)
+            ->and($cases)->toContain(ReasoningEffort::XHIGH);
+    });
+});
diff --git a/tests/Unit/Types/ModelCapabilitiesTest.php b/tests/Unit/Types/ModelCapabilitiesTest.php
index b94b9ff..5001e42 100644
--- a/tests/Unit/Types/ModelCapabilitiesTest.php
+++ b/tests/Unit/Types/ModelCapabilitiesTest.php
@@ -68,4 +68,31 @@
 
         expect($capabilities)->toBeInstanceOf(\Illuminate\Contracts\Support\Arrayable::class);
     });
+
+    it('can check if reasoning effort is supported', function () {
+        $capabilities = ModelCapabilities::fromArray([
+            'supports' => ['vision' => false, 'reasoningEffort' => true],
+            'limits' => ['max_context_window_tokens' => 100000],
+        ]);
+
+        expect($capabilities->supportsReasoningEffort())->toBeTrue();
+    });
+
+    it('returns false when reasoning effort is not supported', function () {
+        $capabilities = ModelCapabilities::fromArray([
+            'supports' => ['vision' => false, 'reasoningEffort' => false],
+            'limits' => ['max_context_window_tokens' => 100000],
+        ]);
+
+        expect($capabilities->supportsReasoningEffort())->toBeFalse();
+    });
+
+    it('returns false when reasoningEffort key is missing', function () {
+        $capabilities = ModelCapabilities::fromArray([
+            'supports' => ['vision' => true],
+            'limits' => ['max_context_window_tokens' => 100000],
+        ]);
+
+        expect($capabilities->supportsReasoningEffort())->toBeFalse();
+    });
 });
diff --git a/tests/Unit/Types/ModelInfoTest.php b/tests/Unit/Types/ModelInfoTest.php
index 9452e42..b95611e 100644
--- a/tests/Unit/Types/ModelInfoTest.php
+++ b/tests/Unit/Types/ModelInfoTest.php
@@ -2,6 +2,7 @@
 
 declare(strict_types=1);
 
+use Revolution\Copilot\Enums\ReasoningEffort;
 use Revolution\Copilot\Types\ModelBilling;
 use Revolution\Copilot\Types\ModelCapabilities;
 use Revolution\Copilot\Types\ModelInfo;
@@ -103,4 +104,69 @@
 
         expect($modelInfo)->toBeInstanceOf(\Illuminate\Contracts\Support\Arrayable::class);
     });
+
+    it('can handle supportedReasoningEfforts array', function () {
+        $modelInfo = ModelInfo::fromArray([
+            'id' => 'reasoning-model',
+            'name' => 'Reasoning Model',
+            'capabilities' => [
+                'supports' => ['vision' => false, 'reasoningEffort' => true],
+                'limits' => ['max_context_window_tokens' => 128000],
+            ],
+            'supportedReasoningEfforts' => ['low', 'medium', 'high'],
+            'defaultReasoningEffort' => 'medium',
+        ]);
+
+        expect($modelInfo->supportedReasoningEfforts)->toBe(['low', 'medium', 'high'])
+            ->and($modelInfo->defaultReasoningEffort)->toBe('medium');
+    });
+
+    it('can handle defaultReasoningEffort as enum', function () {
+        $modelInfo = new ModelInfo(
+            id: 'reasoning-model',
+            name: 'Reasoning Model',
+            capabilities: new ModelCapabilities(
+                supports: ['reasoningEffort' => true],
+                limits: ['max_context_window_tokens' => 128000],
+            ),
+            supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh'],
+            defaultReasoningEffort: ReasoningEffort::HIGH,
+        );
+
+        expect($modelInfo->defaultReasoningEffort)->toBe(ReasoningEffort::HIGH);
+    });
+
+    it('converts defaultReasoningEffort enum to string in toArray', function () {
+        $modelInfo = new ModelInfo(
+            id: 'reasoning-model',
+            name: 'Reasoning Model',
+            capabilities: new ModelCapabilities(
+                supports: ['reasoningEffort' => true],
+                limits: ['max_context_window_tokens' => 128000],
+            ),
+            supportedReasoningEfforts: ['low', 'medium', 'high', 'xhigh'],
+            defaultReasoningEffort: ReasoningEffort::XHIGH,
+        );
+
+        $array = $modelInfo->toArray();
+
+        expect($array['defaultReasoningEffort'])->toBe('xhigh')
+            ->and($array['supportedReasoningEfforts'])->toBe(['low', 'medium', 'high', 'xhigh']);
+    });
+
+    it('excludes reasoning effort fields when null', function () {
+        $modelInfo = new ModelInfo(
+            id: 'basic-model',
+            name: 'Basic Model',
+            capabilities: new ModelCapabilities(
+                supports: ['vision' => false],
+                limits: ['max_context_window_tokens' => 100000],
+            ),
+        );
+
+        $array = $modelInfo->toArray();
+
+        expect($array)->not->toHaveKey('supportedReasoningEfforts')
+            ->and($array)->not->toHaveKey('defaultReasoningEffort');
+    });
 });
diff --git a/tests/Unit/Types/ResumeSessionConfigTest.php b/tests/Unit/Types/ResumeSessionConfigTest.php
index 67d5048..84c9160 100644
--- a/tests/Unit/Types/ResumeSessionConfigTest.php
+++ b/tests/Unit/Types/ResumeSessionConfigTest.php
@@ -2,6 +2,7 @@
 
 declare(strict_types=1);
 
+use Revolution\Copilot\Enums\ReasoningEffort;
 use Revolution\Copilot\Types\ProviderConfig;
 use Revolution\Copilot\Types\ResumeSessionConfig;
 use Revolution\Copilot\Types\SessionHooks;
@@ -135,4 +136,56 @@
 
         expect($config)->toBeInstanceOf(\Illuminate\Contracts\Support\Arrayable::class);
     });
+
+    it('accepts reasoningEffort as enum', function () {
+        $config = new ResumeSessionConfig(
+            reasoningEffort: ReasoningEffort::HIGH,
+        );
+
+        expect($config->reasoningEffort)->toBe(ReasoningEffort::HIGH);
+    });
+
+    it('accepts reasoningEffort as string', function () {
+        $config = new ResumeSessionConfig(
+            reasoningEffort: 'medium',
+        );
+
+        expect($config->reasoningEffort)->toBe('medium');
+    });
+
+    it('converts reasoningEffort enum to string in toArray', function () {
+        $config = new ResumeSessionConfig(
+            reasoningEffort: ReasoningEffort::XHIGH,
+        );
+
+        $array = $config->toArray();
+
+        expect($array['reasoningEffort'])->toBe('xhigh');
+    });
+
+    it('preserves reasoningEffort string in toArray', function () {
+        $config = new ResumeSessionConfig(
+            reasoningEffort: 'low',
+        );
+
+        $array = $config->toArray();
+
+        expect($array['reasoningEffort'])->toBe('low');
+    });
+
+    it('can be created from array with reasoningEffort as string', function () {
+        $config = ResumeSessionConfig::fromArray([
+            'reasoningEffort' => 'high',
+        ]);
+
+        expect($config->reasoningEffort)->toBe('high');
+    });
+
+    it('preserves reasoningEffort enum when passed to fromArray', function () {
+        $config = ResumeSessionConfig::fromArray([
+            'reasoningEffort' => ReasoningEffort::MEDIUM,
+        ]);
+
+        expect($config->reasoningEffort)->toBe(ReasoningEffort::MEDIUM);
+    });
 });
diff --git a/tests/Unit/Types/SessionConfigTest.php b/tests/Unit/Types/SessionConfigTest.php
index 4d1e17e..bae29e3 100644
--- a/tests/Unit/Types/SessionConfigTest.php
+++ b/tests/Unit/Types/SessionConfigTest.php
@@ -2,6 +2,7 @@
 
 declare(strict_types=1);
 
+use Revolution\Copilot\Enums\ReasoningEffort;
 use Revolution\Copilot\Types\InfiniteSessionConfig;
 use Revolution\Copilot\Types\ProviderConfig;
 use Revolution\Copilot\Types\SessionConfig;
@@ -200,4 +201,56 @@
 
         expect($config)->toBeInstanceOf(\Illuminate\Contracts\Support\Arrayable::class);
     });
+
+    it('accepts reasoningEffort as enum', function () {
+        $config = new SessionConfig(
+            reasoningEffort: ReasoningEffort::HIGH,
+        );
+
+        expect($config->reasoningEffort)->toBe(ReasoningEffort::HIGH);
+    });
+
+    it('accepts reasoningEffort as string', function () {
+        $config = new SessionConfig(
+            reasoningEffort: 'medium',
+        );
+
+        expect($config->reasoningEffort)->toBe('medium');
+    });
+
+    it('converts reasoningEffort enum to string in toArray', function () {
+        $config = new SessionConfig(
+            reasoningEffort: ReasoningEffort::XHIGH,
+        );
+
+        $array = $config->toArray();
+
+        expect($array['reasoningEffort'])->toBe('xhigh');
+    });
+
+    it('preserves reasoningEffort string in toArray', function () {
+        $config = new SessionConfig(
+            reasoningEffort: 'low',
+        );
+
+        $array = $config->toArray();
+
+        expect($array['reasoningEffort'])->toBe('low');
+    });
+
+    it('can be created from array with reasoningEffort as string', function () {
+        $config = SessionConfig::fromArray([
+            'reasoningEffort' => 'high',
+        ]);
+
+        expect($config->reasoningEffort)->toBe('high');
+    });
+
+    it('preserves reasoningEffort enum when passed to fromArray', function () {
+        $config = SessionConfig::fromArray([
+            'reasoningEffort' => ReasoningEffort::MEDIUM,
+        ]);
+
+        expect($config->reasoningEffort)->toBe(ReasoningEffort::MEDIUM);
+    });
 });