fix(core): omit deprecated temperature param for Claude 4.8+

packages/core/src/core/anthropicContentGenerator/anthropicContentGenerator.test.ts

@@ -1557,6 +1557,137 @@ describe('AnthropicContentGenerator', () => {
       );
     });
 
+    // Claude 4.8+ deprecated the `temperature` sampling parameter — the
+    // server responds with a 400 when it is sent. Verify the generator
+    // omits it for 4.8+ and keeps it for older models.
+    it('omits temperature on Opus 4.8 (deprecated)', async () => {
+      const { AnthropicContentGenerator } = await importGenerator();
+      anthropicState.createImpl.mockResolvedValue({
+        id: 'anthropic-1',
+        model: 'claude-opus-4-8',
+        content: [{ type: 'text', text: 'hi' }],
+      });
+
+      const generator = new AnthropicContentGenerator(
+        {
+          model: 'claude-opus-4-8',
+          apiKey: 'test-key',
+          baseUrl: 'https://api.anthropic.com',
+          timeout: 10_000,
+          maxRetries: 2,
+          samplingParams: { max_tokens: 500, temperature: 0.7 },
+          schemaCompliance: 'auto',
+        },
+        mockConfig,
+      );
+
+      await generator.generateContent({
+        model: 'models/ignored',
+        contents: 'Hello',
+      } as unknown as GenerateContentParameters);
+
+      const [anthropicRequest] =
+        anthropicState.lastCreateArgs as AnthropicCreateArgs;
+      expect(anthropicRequest).not.toHaveProperty('temperature');
+    });
+
+    it('keeps temperature on Opus 4.7 (still accepted)', async () => {
+      const { AnthropicContentGenerator } = await importGenerator();
+      anthropicState.createImpl.mockResolvedValue({
+        id: 'anthropic-1',
+        model: 'claude-opus-4-7',
+        content: [{ type: 'text', text: 'hi' }],
+      });
+
+      const generator = new AnthropicContentGenerator(
+        {
+          model: 'claude-opus-4-7',
+          apiKey: 'test-key',
+          baseUrl: 'https://api.anthropic.com',
+          timeout: 10_000,
+          maxRetries: 2,
+          samplingParams: { max_tokens: 500, temperature: 0.7 },
+          schemaCompliance: 'auto',
+        },
+        mockConfig,
+      );
+
+      await generator.generateContent({
+        model: 'models/ignored',
+        contents: 'Hello',
+      } as unknown as GenerateContentParameters);
+
+      const [anthropicRequest] =
+        anthropicState.lastCreateArgs as AnthropicCreateArgs;
+      expect(anthropicRequest).toEqual(
+        expect.objectContaining({ temperature: 0.7 }),
+      );
+    });
+
+    it('omits temperature on Sonnet 5 (5.x family, deprecated)', async () => {
+      const { AnthropicContentGenerator } = await importGenerator();
+      anthropicState.createImpl.mockResolvedValue({
+        id: 'anthropic-1',
+        model: 'claude-sonnet-5',
+        content: [{ type: 'text', text: 'hi' }],
+      });
+
+      const generator = new AnthropicContentGenerator(
+        {
+          model: 'claude-sonnet-5',
+          apiKey: 'test-key',
+          baseUrl: 'https://api.anthropic.com',
+          timeout: 10_000,
+          maxRetries: 2,
+          samplingParams: { max_tokens: 500, temperature: 0.5 },
+          schemaCompliance: 'auto',
+        },
+        mockConfig,
+      );
+
+      await generator.generateContent({
+        model: 'models/ignored',
+        contents: 'Hello',
+      } as unknown as GenerateContentParameters);
+
+      const [anthropicRequest] =
+        anthropicState.lastCreateArgs as AnthropicCreateArgs;
+      expect(anthropicRequest).not.toHaveProperty('temperature');
+    });
+
+    it('keeps temperature on unknown/unversioned model id', async () => {
+      const { AnthropicContentGenerator } = await importGenerator();
+      anthropicState.createImpl.mockResolvedValue({
+        id: 'anthropic-1',
+        model: 'some-custom-model',
+        content: [{ type: 'text', text: 'hi' }],
+      });
+
+      const generator = new AnthropicContentGenerator(
+        {
+          model: 'some-custom-model',
+          apiKey: 'test-key',
+          baseUrl: 'https://api.anthropic.com',
+          timeout: 10_000,
+          maxRetries: 2,
+          samplingParams: { max_tokens: 500, temperature: 0.3 },
+          schemaCompliance: 'auto',
+        },
+        mockConfig,
+      );
+
+      await generator.generateContent({
+        model: 'models/ignored',
+        contents: 'Hello',
+      } as unknown as GenerateContentParameters);
+
+      const [anthropicRequest] =
+        anthropicState.lastCreateArgs as AnthropicCreateArgs;
+      expect(anthropicRequest).toEqual(
+        expect.objectContaining({ temperature: 0.3 }),
+      );
+    });
+
     it("clamps effort: 'xhigh' to 'max' on Opus 4.6 (has max, lacks xhigh)", async () => {
       const { AnthropicContentGenerator } = await importGenerator();
       anthropicState.createImpl.mockResolvedValue({

packages/core/src/core/anthropicContentGenerator/anthropicContentGenerator.ts

@@ -271,6 +271,7 @@ export class AnthropicContentGenerator implements ContentGenerator {
   // instead of on every request that needs the downgrade.
   private effortClampWarned = false;
   private budgetDropWarned = false;
+  private temperatureDropWarned = false;
 
   constructor(
     private contentGeneratorConfig: ContentGeneratorConfig,
@@ -744,9 +745,27 @@ export class AnthropicContentGenerator implements ContentGenerator {
       }
     }
 
+    // Claude 4.8+ deprecated temperature — the server rejects it with a 400.
+    // Omit the parameter entirely for those models; older models keep the
+    // default of 1 (Anthropic's documented neutral value).
+    const temperatureDropped = this.modelRejectsTemperature();
+    if (temperatureDropped && !this.temperatureDropWarned) {
+      const userTemp = getParam<number>('temperature', 'temperature');
+      if (userTemp !== undefined) {
+        debugLogger.warn(
+          `temperature=${userTemp} is not supported by '${
+            this.contentGeneratorConfig.model ?? 'unknown'
+          }' (deprecated on 4.8+); ignoring.`,
+        );
+      }
+      this.temperatureDropWarned = true;
+    }
+
     return {
       max_tokens: maxTokens,
-      temperature: getParam<number>('temperature', 'temperature') ?? 1,
+      ...(temperatureDropped
+        ? {}
+        : { temperature: getParam<number>('temperature', 'temperature') ?? 1 }),
       top_p: getParam<number>('top_p', 'topP'),
       top_k: getParam<number>('top_k', 'topK'),
     };
@@ -858,6 +877,23 @@ export class AnthropicContentGenerator implements ContentGenerator {
     return major > 4 || (major === 4 && minor >= 7);
   }
 
+  /**
+   * Whether the model rejects the `temperature` sampling parameter with a 400.
+   * Claude Opus 4.8+ deprecated temperature — the server controls sampling
+   * determinism internally and responds with
+   * `"temperature is deprecated for this model."` when the parameter is sent.
+   * Older models (4.7 and below) and unknown/unversioned ids still accept it,
+   * so both return false.
+   */
+  private modelRejectsTemperature(): boolean {
+    const parsed = parseClaudeModelVersion(
+      this.contentGeneratorConfig.model || '',
+    );
+    if (!parsed) return false;
+    const { major, minor } = parsed;
+    return major > 4 || (major === 4 && minor >= 8);
+  }
+
   private buildThinkingConfig(
     request: GenerateContentParameters,
     effectiveEffort: ReasoningEffort | undefined,