fix(openai): omit temperature when no custom value is set (#242)

src/api/providers/__tests__/openai.spec.ts

@@ -409,13 +409,15 @@ describe("OpenAiHandler", () => {
 			expect(callArgs).not.toHaveProperty("temperature")
 		})
 
-		it("should include temperature by default when supportsTemperature is not set", async () => {
+		it("should omit temperature by default when no custom temperature is set", async () => {
+			// Option A: when "use custom temperature" is off (modelTemperature unset) and the model has no
+			// required default, omit `temperature` so the server's own default applies instead of forcing 0.
 			const stream = handler.createMessage(systemPrompt, messages)
 			for await (const _chunk of stream) {
 			}
 			expect(mockCreate).toHaveBeenCalled()
 			const callArgs = mockCreate.mock.calls[0][0]
-			expect(callArgs).toHaveProperty("temperature")
+			expect(callArgs).not.toHaveProperty("temperature")
 		})
 
 		it("should use the configured modelTemperature when supportsTemperature is not false", async () => {
@@ -438,6 +440,17 @@ describe("OpenAiHandler", () => {
 			expect(callArgs.temperature).toBe(DEEP_SEEK_DEFAULT_TEMPERATURE)
 		})
 
+		it("should still send temperature when the user sets a custom value of 0", async () => {
+			// A deliberate 0 must be distinguished from "unset" — it is sent, not omitted.
+			const zeroTempHandler = new OpenAiHandler({ ...mockOptions, modelTemperature: 0 })
+			const stream = zeroTempHandler.createMessage(systemPrompt, messages)
+			for await (const _chunk of stream) {
+			}
+			expect(mockCreate).toHaveBeenCalled()
+			const callArgs = mockCreate.mock.calls[0][0]
+			expect(callArgs.temperature).toBe(0)
+		})
+
 		it("should include max_tokens when includeMaxTokens is true", async () => {
 			const optionsWithMaxTokens: ApiHandlerOptions = {
 				...mockOptions,
@@ -679,7 +692,7 @@ describe("OpenAiHandler", () => {
 					],
 					stream: true,
 					stream_options: { include_usage: true },
-					temperature: 0,
+					// No custom temperature set → `temperature` is omitted.
 					tools: undefined,
 					tool_choice: undefined,
 					parallel_tool_calls: true,

src/api/providers/openai.ts

@@ -155,13 +155,14 @@ export class OpenAiHandler extends BaseProvider implements SingleCompletionHandl
 			const requestOptions: OpenAI.Chat.Completions.ChatCompletionCreateParamsStreaming = {
 				model: modelId,
 				// Some OpenAI-Compatible models (e.g. claude-opus-4-7, claude-opus-4-8) reject
-				// `temperature` as deprecated/unsupported. Honor the model's `supportsTemperature`
-				// flag and omit it when explicitly set to false (undefined still sends temperature,
-				// preserving behavior).
-				...(modelInfo.supportsTemperature !== false && {
-					temperature:
-						this.options.modelTemperature ?? (deepseekReasoner ? DEEP_SEEK_DEFAULT_TEMPERATURE : 0),
-				}),
+				// `temperature` as deprecated/unsupported, so honor the model's `supportsTemperature`
+				// flag and omit it when that flag is false. Beyond that, only send `temperature` when
+				// the user set a custom value or the model needs a specific default (deepseek-reasoner);
+				// otherwise omit it so the server's own default applies instead of forcing 0.
+				...(modelInfo.supportsTemperature !== false &&
+					(this.options.modelTemperature != null || deepseekReasoner) && {
+						temperature: this.options.modelTemperature ?? DEEP_SEEK_DEFAULT_TEMPERATURE,
+					}),
 				messages: convertedMessages,
 				stream: true as const,
 				...(isGrokXAI ? {} : { stream_options: { include_usage: true } }),