[Feature] Add Gemini 3.1 Flash Image Preview input and output cost details

Author: davidvpe

model_prices_and_context_window.json

@@ -16422,22 +16422,25 @@
         "supports_web_search": true
     },
     "gemini/gemini-3.1-flash-image-preview": {
-        "input_cost_per_image": 0.0001375,
         "input_cost_per_token": 2.5e-07,
+        "input_cost_per_token_batches": 1.25e-07,
         "litellm_provider": "gemini",
         "max_input_tokens": 65536,
         "max_output_tokens": 32768,
         "max_tokens": 32768,
         "mode": "image_generation",
         "output_cost_per_image": 0.045,
         "output_cost_per_image_token": 6e-05,
+        "output_cost_per_image_token_batches": 3e-05,
         "output_cost_per_token": 1.5e-06,
+        "output_cost_per_token_batches": 7.5e-07,
         "rpm": 1000,
         "tpm": 4000000,
         "source": "https://ai.google.dev/gemini-api/docs/pricing#gemini-3.1-flash-image-preview",
         "supported_endpoints": [
             "/v1/chat/completions",
-            "/v1/completions"
+            "/v1/completions",
+            "/v1/batch"
         ],
         "supported_modalities": [
             "text",