diff --git a/src/providers/openrouter/chatComplete.test.ts b/src/providers/openrouter/chatComplete.test.ts
new file mode 100644
index 000000000..4a4800c0b
--- /dev/null
+++ b/src/providers/openrouter/chatComplete.test.ts
@@ -0,0 +1,72 @@
+import { Params } from '../../types/requestBody';
+import { OpenrouterChatCompleteConfig } from './chatComplete';
+
+describe('OpenrouterChatCompleteConfig', () => {
+  it('preserves OpenRouter chat and routing parameters', () => {
+    const passthroughParameters = [
+      'model',
+      'max_tokens',
+      'max_completion_tokens',
+      'temperature',
+      'cache_control',
+      'debug',
+      'frequency_penalty',
+      'image_config',
+      'logit_bias',
+      'logprobs',
+      'metadata',
+      'min_p',
+      'modalities',
+      'models',
+      'parallel_tool_calls',
+      'plugins',
+      'presence_penalty',
+      'provider',
+      'reasoning',
+      'reasoning_effort',
+      'repetition_penalty',
+      'response_format',
+      'route',
+      'seed',
+      'service_tier',
+      'session_id',
+      'stop',
+      'stop_server_tools_when',
+      'stream',
+      'stream_options',
+      'tool_choice',
+      'tools',
+      'top_a',
+      'top_k',
+      'top_logprobs',
+      'top_p',
+      'trace',
+      'transforms',
+      'usage',
+      'user',
+    ];
+
+    for (const parameter of passthroughParameters) {
+      expect(OpenrouterChatCompleteConfig[parameter]).toMatchObject({
+        param: parameter,
+      });
+    }
+  });
+
+  it('maps developer messages to OpenRouter-compatible system messages', () => {
+    const params = {
+      model: 'google/gemini-2.5-flash',
+      messages: [{ role: 'developer', content: 'Follow this instruction' }],
+    } as Params;
+
+    const messageConfig = OpenrouterChatCompleteConfig.messages;
+    expect(Array.isArray(messageConfig)).toBe(false);
+    const transformed = !Array.isArray(messageConfig)
+      ? messageConfig.transform?.(params, { provider: 'openrouter' })
+      : undefined;
+
+    expect(transformed).toEqual([
+      { role: 'system', content: 'Follow this instruction' },
+    ]);
+  });
+});
diff --git a/src/providers/openrouter/chatComplete.ts b/src/providers/openrouter/chatComplete.ts
index 049c41717..717f0635e 100644
--- a/src/providers/openrouter/chatComplete.ts
+++ b/src/providers/openrouter/chatComplete.ts
@@ -10,7 +10,6 @@ import {
   generateErrorResponse,
   generateInvalidProviderResponseError,
 } from '../utils';
-import { transformReasoningParams, transformUsageOptions } from './utils';
 
 export const OpenrouterChatCompleteConfig: ProviderConfig = {
   model: {
@@ -34,7 +33,7 @@ export const OpenrouterChatCompleteConfig: ProviderConfig = {
     min: 0,
   },
   max_completion_tokens: {
-    param: 'max_tokens',
+    param: 'max_completion_tokens',
     default: 100,
     min: 0,
   },
@@ -47,17 +46,39 @@ export const OpenrouterChatCompleteConfig: ProviderConfig = {
   modalities: {
     param: 'modalities',
   },
+  cache_control: {
+    param: 'cache_control',
+  },
+  debug: {
+    param: 'debug',
+  },
+  frequency_penalty: {
+    param: 'frequency_penalty',
+    min: -2,
+    max: 2,
+  },
+  image_config: {
+    param: 'image_config',
+  },
+  logit_bias: {
+    param: 'logit_bias',
+  },
+  logprobs: {
+    param: 'logprobs',
+  },
+  metadata: {
+    param: 'metadata',
+  },
+  min_p: {
+    param: 'min_p',
+    min: 0,
+    max: 1,
+  },
   reasoning: {
     param: 'reasoning',
-    transform: (params: Params) => {
-      return transformReasoningParams(params);
-    },
   },
   reasoning_effort: {
-    param: 'reasoning',
-    transform: (params: Params) => {
-      return transformReasoningParams(params);
-    },
+    param: 'reasoning_effort',
   },
   top_p: {
     param: 'top_p',
@@ -65,6 +86,38 @@ export const OpenrouterChatCompleteConfig: ProviderConfig = {
     min: 0,
     max: 1,
   },
+  parallel_tool_calls: {
+    param: 'parallel_tool_calls',
+  },
+  plugins: {
+    param: 'plugins',
+  },
+  presence_penalty: {
+    param: 'presence_penalty',
+    min: -2,
+    max: 2,
+  },
+  repetition_penalty: {
+    param: 'repetition_penalty',
+  },
+  route: {
+    param: 'route',
+  },
+  seed: {
+    param: 'seed',
+  },
+  service_tier: {
+    param: 'service_tier',
+  },
+  session_id: {
+    param: 'session_id',
+  },
+  stop: {
+    param: 'stop',
+  },
+  stop_server_tools_when: {
+    param: 'stop_server_tools_when',
+  },
   tools: {
     param: 'tools',
   },
@@ -82,23 +135,32 @@ export const OpenrouterChatCompleteConfig: ProviderConfig = {
   },
   usage: {
     param: 'usage',
-    transform: (params: Params) => {
-      return transformUsageOptions(params);
-    },
   },
   stream: {
     param: 'stream',
     default: false,
   },
   stream_options: {
-    param: 'usage',
-    transform: (params: Params) => {
-      return transformUsageOptions(params);
-    },
+    param: 'stream_options',
   },
   response_format: {
     param: 'response_format',
   },
+  top_a: {
+    param: 'top_a',
+  },
+  top_k: {
+    param: 'top_k',
+  },
+  top_logprobs: {
+    param: 'top_logprobs',
+  },
+  trace: {
+    param: 'trace',
+  },
+  user: {
+    param: 'user',
+  },
 };
 
 interface OpenrouterUsageDetails {
diff --git a/src/providers/openrouter/utils.ts b/src/providers/openrouter/utils.ts
deleted file mode 100644
index 72ab76108..000000000
--- a/src/providers/openrouter/utils.ts
+++ /dev/null
@@ -1,35 +0,0 @@
-import { Params } from '../../types/requestBody';
-
-interface OpenrouterUsageParam {
-  include?: boolean;
-}
-
-interface OpenRouterParams extends Params {
-  reasoning?: OpenrouterReasoningParam;
-  usage?: OpenrouterUsageParam;
-  stream_options?: {
-    include_usage?: boolean;
-  };
-}
-
-type OpenrouterReasoningParam = {
-  effort?: 'low' | 'medium' | 'high' | string;
-  max_tokens?: number;
-  exclude?: boolean;
-};
-
-export const transformReasoningParams = (params: OpenRouterParams) => {
-  let reasoning: OpenrouterReasoningParam = { ...params.reasoning };
-  if (params.reasoning_effort) {
-    reasoning.effort = params.reasoning_effort;
-  }
-  return Object.keys(reasoning).length > 0 ? reasoning : null;
-};
-
-export const transformUsageOptions = (params: OpenRouterParams) => {
-  let usage: OpenrouterUsageParam = { ...params.usage };
-  if (params.stream_options?.include_usage) {
-    usage.include = params.stream_options?.include_usage;
-  }
-  return Object.keys(usage).length > 0 ? usage : null;
-};