feat(openai): add gpt-image-2 to model prices and context window

gpt-image-2 was released on 2026-04-21 and is available in the API.
This adds pricing entries for the model:

- Base entry: $8/1M image input tokens, $32/1M image output tokens
- Per-quality per-size entries for low/medium/high at 1024x1024:
  - low:    $0.006/image
  - medium: $0.053/image
  - high:   $0.211/image

Closes #26232

Relates to litellm_oss_branch

litellm/model_prices_and_context_window_backup.json

@@ -18268,6 +18268,18 @@
         "supports_vision": true,
         "supports_pdf_input": true
     },
+    "gpt-image-2": {
+        "input_cost_per_token": 8e-06,
+        "input_cost_per_image_token": 8e-06,
+        "output_cost_per_image_token": 3.2e-05,
+        "litellm_provider": "openai",
+        "mode": "image_generation",
+        "supported_endpoints": [
+            "/v1/images/generations",
+            "/v1/images/edits"
+        ],
+        "supports_vision": true
+    },
     "low/1024-x-1024/gpt-image-1.5": {
         "input_cost_per_image": 0.009,
         "litellm_provider": "openai",
@@ -18598,6 +18610,36 @@
         "supports_vision": true,
         "supports_pdf_input": true
     },
+    "low/1024-x-1024/gpt-image-2": {
+        "input_cost_per_image": 0.006,
+        "litellm_provider": "openai",
+        "mode": "image_generation",
+        "supported_endpoints": [
+            "/v1/images/generations",
+            "/v1/images/edits"
+        ],
+        "supports_vision": true
+    },
+    "medium/1024-x-1024/gpt-image-2": {
+        "input_cost_per_image": 0.053,
+        "litellm_provider": "openai",
+        "mode": "image_generation",
+        "supported_endpoints": [
+            "/v1/images/generations",
+            "/v1/images/edits"
+        ],
+        "supports_vision": true
+    },
+    "high/1024-x-1024/gpt-image-2": {
+        "input_cost_per_image": 0.211,
+        "litellm_provider": "openai",
+        "mode": "image_generation",
+        "supported_endpoints": [
+            "/v1/images/generations",
+            "/v1/images/edits"
+        ],
+        "supports_vision": true
+    },
     "gpt-5": {
         "cache_read_input_token_cost": 1.25e-07,
         "cache_read_input_token_cost_flex": 6.25e-08,

tests/test_litellm/test_gpt_image_cost_calculator.py

@@ -8,6 +8,10 @@ gpt-image-1 uses token-based pricing:
 - Text Input: $5.00/1M tokens
 - Image Input: $10.00/1M tokens
 - Image Output: $40.00/1M tokens
+
+gpt-image-2 uses token-based pricing:
+- Image Input: $8.00/1M tokens
+- Image Output: $32.00/1M tokens
 """
 
 import os
@@ -305,3 +309,64 @@ class TestCompletionCostIntegration:
 
 if __name__ == "__main__":
     pytest.main([__file__, "-v"])
+
+
+class TestGPTImage2CostCalculator:
+    """Test the OpenAI gpt-image-2 cost calculator.
+
+    gpt-image-2 pricing (https://openai.com/api/pricing/):
+    - Image Input:  $8.00 / 1M tokens  (8e-6 per token)
+    - Image Output: $32.00 / 1M tokens (3.2e-5 per token)
+    """
+
+    def test_gpt_image_2_token_cost(self):
+        """Test token-based cost calculation for gpt-image-2."""
+        from litellm.llms.openai.image_generation.cost_calculator import cost_calculator
+
+        usage = ImageUsage(
+            input_tokens=1000,
+            output_tokens=5000,
+            total_tokens=6000,
+            input_tokens_details=ImageUsageInputTokensDetails(
+                text_tokens=0,
+                image_tokens=1000,
+            ),
+        )
+
+        image_response = ImageResponse(
+            created=1234567890,
+            data=[ImageObject(url="http://example.com/image.jpg")],
+        )
+        image_response.usage = usage
+
+        cost = cost_calculator(
+            model="gpt-image-2",
+            image_response=image_response,
+            custom_llm_provider="openai",
+        )
+
+        # Expected cost:
+        # Image input:  1000 * $8/1M  = 0.008
+        # Image output: 5000 * $32/1M = 0.16
+        # Total: 0.168
+        expected_cost = 1000 * 8e-6 + 5000 * 3.2e-5
+        assert abs(cost - expected_cost) < 1e-6, f"Expected {expected_cost}, got {cost}"
+
+    def test_gpt_image_2_in_model_prices(self):
+        """Test that gpt-image-2 is present in the model prices registry."""
+        model_info = litellm.get_model_info("gpt-image-2")
+        assert model_info is not None, "gpt-image-2 not found in model prices"
+        assert model_info.get("litellm_provider") == "openai"
+        assert model_info.get("mode") == "image_generation"
+        assert model_info.get("input_cost_per_image_token") == 8e-6
+        assert model_info.get("output_cost_per_image_token") == 3.2e-5
+
+    def test_gpt_image_2_per_quality_entries(self):
+        """Test that per-quality per-size entries exist for gpt-image-2."""
+        for quality in ("low", "medium", "high"):
+            key = f"{quality}/1024-x-1024/gpt-image-2"
+            model_info = litellm.get_model_info(key)
+            assert model_info is not None, f"{key} not found in model prices"
+            assert model_info.get("litellm_provider") == "openai"
+            assert model_info.get("mode") == "image_generation"
+            assert model_info.get("input_cost_per_image") is not None