feat: hardcode temperature to 1 for GPT-5 models

- Set temperature to 1 for all GPT-5 model variants (gpt-5, gpt-5-mini, gpt-5-nano)
- Added comprehensive tests to verify temperature hardcoding
- Ensures consistent behavior for GPT-5 models as requested

src/api/transform/__tests__/model-params.spec.ts

@@ -885,4 +885,136 @@ describe("getModelParams", () => {
 			expect(result.reasoningBudget).toBe(8192) // Default thinking tokens
 		})
 	})
+
+	describe("GPT-5 temperature hardcoding", () => {
+		it("should hardcode temperature to 1 for gpt-5 models", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-2025-08-07",
+				format: "openai" as const,
+				settings: { modelTemperature: 0.5 }, // User setting should be overridden
+				model,
+			})
+
+			expect(result.temperature).toBe(1)
+		})
+
+		it("should hardcode temperature to 1 for gpt-5-mini models", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-mini-2025-08-07",
+				format: "openai" as const,
+				settings: { modelTemperature: 0.7 }, // User setting should be overridden
+				model,
+			})
+
+			expect(result.temperature).toBe(1)
+		})
+
+		it("should hardcode temperature to 1 for gpt-5-nano models", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-nano-2025-08-07",
+				format: "openai" as const,
+				settings: { modelTemperature: 0.3 }, // User setting should be overridden
+				model,
+			})
+
+			expect(result.temperature).toBe(1)
+		})
+
+		it("should hardcode temperature to 1 even when no temperature is specified for gpt-5", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-2025-08-07",
+				format: "openai" as const,
+				settings: {}, // No temperature specified
+				model,
+				defaultTemperature: 0.2, // Default should also be overridden
+			})
+
+			expect(result.temperature).toBe(1)
+		})
+
+		it("should not hardcode temperature for non-gpt-5 openai models", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-4-turbo",
+				format: "openai" as const,
+				settings: { modelTemperature: 0.5 },
+				model,
+			})
+
+			expect(result.temperature).toBe(0.5)
+		})
+
+		it("should not hardcode temperature for gpt-5 models in non-openai format", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-2025-08-07",
+				format: "openrouter" as const,
+				settings: { modelTemperature: 0.5 },
+				model,
+			})
+
+			expect(result.temperature).toBe(0.5) // Should not be hardcoded for openrouter
+		})
+
+		it("should hardcode temperature for gpt-5 with reasoning effort", () => {
+			const model: ModelInfo = {
+				...baseModel,
+				supportsReasoningEffort: true,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-2025-08-07",
+				format: "openai" as const,
+				settings: {
+					modelTemperature: 0.5,
+					reasoningEffort: "high",
+				},
+				model,
+			})
+
+			expect(result.temperature).toBe(1)
+			expect(result.reasoningEffort).toBe("high")
+		})
+
+		it("should hardcode temperature for gpt-5 with verbosity settings", () => {
+			const model: ModelInfo = {
+				...baseModel,
+			}
+
+			const result = getModelParams({
+				modelId: "gpt-5-2025-08-07",
+				format: "openai" as const,
+				settings: {
+					modelTemperature: 0.5,
+					verbosity: "high",
+				},
+				model,
+			})
+
+			expect(result.temperature).toBe(1)
+			expect(result.verbosity).toBe("high")
+		})
+	})
 })

src/api/transform/model-params.ts

@@ -146,6 +146,11 @@ export function getModelParams({
 			params.temperature = undefined
 		}
 
+		// Hardcode temperature to 1 for GPT-5 models
+		if (modelId.startsWith("gpt-5")) {
+			params.temperature = 1
+		}
+
 		return {
 			format,
 			...params,