diff --git a/src/api/providers/__tests__/openai-native.spec.ts b/src/api/providers/__tests__/openai-native.spec.ts
index 1d76d387a9f..cdf52da7889 100644
--- a/src/api/providers/__tests__/openai-native.spec.ts
+++ b/src/api/providers/__tests__/openai-native.spec.ts
@@ -634,7 +634,8 @@ describe("OpenAiNativeHandler", () => {
 			expect(body1).toContain('"effort":"medium"')
 			expect(body1).toContain('"summary":"auto"')
 			expect(body1).toContain('"verbosity":"medium"')
-			expect(body1).toContain('"temperature":1')
+			// GPT-5 no longer supports temperature parameter
+			expect(body1).not.toContain('"temperature"')
 			expect(body1).toContain('"max_output_tokens"')
 
 			// Verify the streamed content
@@ -856,7 +857,8 @@ describe("OpenAiNativeHandler", () => {
 			expect(body2).toContain('"effort":"low"')
 			expect(body2).toContain('"summary":"auto"')
 			expect(body2).toContain('"verbosity":"medium"')
-			expect(body2).toContain('"temperature":1')
+			// GPT-5 no longer supports temperature parameter
+			expect(body2).not.toContain('"temperature"')
 			expect(body2).toContain('"max_output_tokens"')
 
 			// Clean up
@@ -906,7 +908,8 @@ describe("OpenAiNativeHandler", () => {
 			expect(body3).toContain('"effort":"minimal"')
 			expect(body3).toContain('"summary":"auto"')
 			expect(body3).toContain('"verbosity":"high"')
-			expect(body3).toContain('"temperature":1')
+			// GPT-5 no longer supports temperature parameter
+			expect(body3).not.toContain('"temperature"')
 			expect(body3).toContain('"max_output_tokens"')
 
 			// Clean up
diff --git a/src/api/providers/openai-native.ts b/src/api/providers/openai-native.ts
index 053af7f5e5f..662d0e42edd 100644
--- a/src/api/providers/openai-native.ts
+++ b/src/api/providers/openai-native.ts
@@ -273,7 +273,7 @@ export class OpenAiNativeHandler extends BaseProvider implements SingleCompletio
 			stream: boolean
 			reasoning?: { effort: ReasoningEffortWithMinimal; summary?: "auto" }
 			text?: { verbosity: VerbosityLevel }
-			temperature?: number
+			// temperature parameter removed - GPT-5 no longer supports it
 			max_output_tokens?: number
 			previous_response_id?: string
 		}
@@ -289,7 +289,7 @@ export class OpenAiNativeHandler extends BaseProvider implements SingleCompletio
 				},
 			}),
 			text: { verbosity: (verbosity || "medium") as VerbosityLevel },
-			temperature: this.options.modelTemperature ?? GPT5_DEFAULT_TEMPERATURE,
+			// GPT-5 no longer supports temperature parameter
 			// Explicitly include the calculated max output tokens for GPT‑5.
 			// Use the per-request reserved output computed by Roo (params.maxTokens from getModelParams).
 			...(model.maxTokens ? { max_output_tokens: model.maxTokens } : {}),
diff --git a/src/api/transform/model-params.ts b/src/api/transform/model-params.ts
index 933697c0a53..2d5ff167436 100644
--- a/src/api/transform/model-params.ts
+++ b/src/api/transform/model-params.ts
@@ -142,9 +142,9 @@ export function getModelParams({
 			reasoning: getAnthropicReasoning({ model, reasoningBudget, reasoningEffort, settings }),
 		}
 	} else if (format === "openai") {
-		// Special case for o1 and o3-mini, which don't support temperature.
+		// Special case for o1, o3-mini, and GPT-5 models, which don't support temperature.
 		// TODO: Add a `supportsTemperature` field to the model info.
-		if (modelId.startsWith("o1") || modelId.startsWith("o3-mini")) {
+		if (modelId.startsWith("o1") || modelId.startsWith("o3-mini") || modelId.startsWith("gpt-5")) {
 			params.temperature = undefined
 		}