fix(provider): use snake_case for thinking param with OpenAI-compatible APIs (#10109)

packages/opencode/test/provider/transform.test.ts

@@ -267,6 +267,56 @@ describe("ProviderTransform.maxOutputTokens", () => {
       expect(result).toBe(OUTPUT_TOKEN_MAX)
     })
   })
+
+  describe("openai-compatible with thinking options (snake_case)", () => {
+    test("returns 32k when budget_tokens + 32k <= modelLimit", () => {
+      const modelLimit = 100000
+      const options = {
+        thinking: {
+          type: "enabled",
+          budget_tokens: 10000,
+        },
+      }
+      const result = ProviderTransform.maxOutputTokens("@ai-sdk/openai-compatible", options, modelLimit, OUTPUT_TOKEN_MAX)
+      expect(result).toBe(OUTPUT_TOKEN_MAX)
+    })
+
+    test("returns modelLimit - budget_tokens when budget_tokens + 32k > modelLimit", () => {
+      const modelLimit = 50000
+      const options = {
+        thinking: {
+          type: "enabled",
+          budget_tokens: 30000,
+        },
+      }
+      const result = ProviderTransform.maxOutputTokens("@ai-sdk/openai-compatible", options, modelLimit, OUTPUT_TOKEN_MAX)
+      expect(result).toBe(20000)
+    })
+
+    test("returns 32k when thinking type is not enabled", () => {
+      const modelLimit = 100000
+      const options = {
+        thinking: {
+          type: "disabled",
+          budget_tokens: 10000,
+        },
+      }
+      const result = ProviderTransform.maxOutputTokens("@ai-sdk/openai-compatible", options, modelLimit, OUTPUT_TOKEN_MAX)
+      expect(result).toBe(OUTPUT_TOKEN_MAX)
+    })
+
+    test("returns 32k when budget_tokens is 0", () => {
+      const modelLimit = 100000
+      const options = {
+        thinking: {
+          type: "enabled",
+          budget_tokens: 0,
+        },
+      }
+      const result = ProviderTransform.maxOutputTokens("@ai-sdk/openai-compatible", options, modelLimit, OUTPUT_TOKEN_MAX)
+      expect(result).toBe(OUTPUT_TOKEN_MAX)
+    })
+  })
 })
 
 describe("ProviderTransform.schema - gemini array items", () => {
@@ -1494,6 +1544,67 @@ describe("ProviderTransform.variants", () => {
       expect(result.low).toEqual({ reasoningEffort: "low" })
       expect(result.high).toEqual({ reasoningEffort: "high" })
     })
+
+    test("Claude via LiteLLM returns thinking with snake_case budget_tokens", () => {
+      const model = createMockModel({
+        id: "anthropic/claude-sonnet-4-5",
+        providerID: "anthropic",
+        api: {
+          id: "claude-sonnet-4-5-20250929",
+          url: "http://localhost:4000",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["high", "max"])
+      expect(result.high).toEqual({
+        thinking: {
+          type: "enabled",
+          budget_tokens: 16000,
+        },
+      })
+      expect(result.max).toEqual({
+        thinking: {
+          type: "enabled",
+          budget_tokens: 31999,
+        },
+      })
+    })
+
+    test("Claude model (by model.id) via openai-compatible uses snake_case", () => {
+      const model = createMockModel({
+        id: "litellm/claude-3-opus",
+        providerID: "litellm",
+        api: {
+          id: "claude-3-opus-20240229",
+          url: "http://localhost:4000",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["high", "max"])
+      expect(result.high).toEqual({
+        thinking: {
+          type: "enabled",
+          budget_tokens: 16000,
+        },
+      })
+    })
+
+    test("Anthropic model (by model.api.id) via openai-compatible uses snake_case", () => {
+      const model = createMockModel({
+        id: "custom/my-model",
+        providerID: "custom",
+        api: {
+          id: "anthropic.claude-sonnet",
+          url: "http://localhost:4000",
+          npm: "@ai-sdk/openai-compatible",
+        },
+      })
+      const result = ProviderTransform.variants(model)
+      expect(Object.keys(result)).toEqual(["high", "max"])
+      expect(result.high.thinking.budget_tokens).toBe(16000)
+    })
   })
 
   describe("@ai-sdk/azure", () => {