feat(js/plugins/anthropic): add structured output support

js/package.json

@@ -31,7 +31,10 @@
   },
   "pnpm": {
     "overrides": {
-      "cross-spawn": "^7.0.5"
+      "cross-spawn": "^7.0.5",
+      "@genkit-ai/vertexai>@anthropic-ai/sdk": "^0.24.3",
+      "@anthropic-ai/vertex-sdk>@anthropic-ai/sdk": "^0.24.3",
+      "@genkit-ai/anthropic>@anthropic-ai/sdk": "^0.71.2"
     }
   },
   "packageManager": "pnpm@10.26.0+sha512.3b3f6c725ebe712506c0ab1ad4133cf86b1f4b687effce62a9b38b4d72e3954242e643190fc51fa1642949c735f403debd44f5cb0edd657abe63a8b6a7e1e402"

js/plugins/anthropic/package.json

@@ -29,7 +29,7 @@
     "genkit": "workspace:^"
   },
   "dependencies": {
-    "@anthropic-ai/sdk": "^0.68.0"
+    "@anthropic-ai/sdk": "^0.71.2"
   },
   "devDependencies": {
     "@types/node": "^20.11.16",
@@ -64,6 +64,7 @@
     "build": "npm-run-all build:clean check compile",
     "build:watch": "tsup-node --watch",
     "test": "tsx --test tests/*_test.ts",
+    "test:live": "tsx --test tests/live_test.ts",
     "test:file": "tsx --test",
     "test:live": "tsx --test tests/live_test.ts",
     "test:coverage": "check-node-version --node '>=22' && tsx --test --experimental-test-coverage --test-coverage-include='src/**/*.ts' ./tests/**/*_test.ts"

js/plugins/anthropic/src/models.ts

@@ -91,19 +91,59 @@ export const KNOWN_CLAUDE_MODELS: Record<
   'claude-opus-4': commonRef('claude-opus-4', AnthropicThinkingConfigSchema),
   'claude-sonnet-4-5': commonRef(
     'claude-sonnet-4-5',
-    AnthropicThinkingConfigSchema
+    AnthropicThinkingConfigSchema,
+    {
+      supports: {
+        multiturn: true,
+        tools: true,
+        media: true,
+        systemRole: true,
+        output: ['text', 'json'],
+        constrained: 'all',
+      },
+    }
   ),
   'claude-haiku-4-5': commonRef(
     'claude-haiku-4-5',
-    AnthropicThinkingConfigSchema
+    AnthropicThinkingConfigSchema,
+    {
+      supports: {
+        multiturn: true,
+        tools: true,
+        media: true,
+        systemRole: true,
+        output: ['text', 'json'],
+        constrained: 'all',
+      },
+    }
   ),
   'claude-opus-4-5': commonRef(
     'claude-opus-4-5',
-    AnthropicThinkingConfigSchema
+    AnthropicThinkingConfigSchema,
+    {
+      supports: {
+        multiturn: true,
+        tools: true,
+        media: true,
+        systemRole: true,
+        output: ['text', 'json'],
+        constrained: 'all',
+      },
+    }
   ),
   'claude-opus-4-1': commonRef(
     'claude-opus-4-1',
-    AnthropicThinkingConfigSchema
+    AnthropicThinkingConfigSchema,
+    {
+      supports: {
+        multiturn: true,
+        tools: true,
+        media: true,
+        systemRole: true,
+        output: ['text', 'json'],
+        constrained: 'all',
+      },
+    }
   ),
 };
 
@@ -232,9 +272,11 @@ export function claudeModel(
     defaultApiVersion: apiVersion,
   } = params;
   // Use supported model ref if available, otherwise create generic model ref
-  const modelRef = KNOWN_CLAUDE_MODELS[name];
-  const modelInfo = modelRef ? modelRef.info : GENERIC_CLAUDE_MODEL_INFO;
-  const configSchema = modelRef?.configSchema ?? AnthropicConfigSchema;
+  const knownModelRef = KNOWN_CLAUDE_MODELS[name];
+  let modelInfo = knownModelRef
+    ? knownModelRef.info
+    : GENERIC_CLAUDE_MODEL_INFO;
+  const configSchema = knownModelRef?.configSchema ?? AnthropicConfigSchema;
 
   return model<
     AnthropicBaseConfigSchemaType | AnthropicThinkingConfigSchemaType

js/plugins/anthropic/src/runner/beta.ts

@@ -66,6 +66,57 @@ const BETA_UNSUPPORTED_SERVER_TOOL_BLOCK_TYPES = new Set<string>([
   'container_upload',
 ]);
 
+const BETA_APIS = [
+  // 'message-batches-2024-09-24',
+  // 'prompt-caching-2024-07-31',
+  // 'computer-use-2025-01-24',
+  // 'pdfs-2024-09-25',
+  // 'token-counting-2024-11-01',
+  // 'token-efficient-tools-2025-02-19',
+  // 'output-128k-2025-02-19',
+  // 'files-api-2025-04-14',
+  // 'mcp-client-2025-04-04',
+  // 'dev-full-thinking-2025-05-14',
+  // 'interleaved-thinking-2025-05-14',
+  // 'code-execution-2025-05-22',
+  // 'extended-cache-ttl-2025-04-11',
+  // 'context-1m-2025-08-07',
+  // 'context-management-2025-06-27',
+  // 'model-context-window-exceeded-2025-08-26',
+  // 'skills-2025-10-02',
+  // 'effort-param-2025-11-24',
+  // 'advanced-tool-use-2025-11-20',
+  'structured-outputs-2025-11-13',
+];
+
+/**
+ * Transforms a JSON schema to be compatible with Anthropic's structured output requirements.
+ * Anthropic requires `additionalProperties: false` on all object types.
+ * @see https://docs.anthropic.com/en/docs/build-with-claude/structured-outputs#json-schema-limitations
+ */
+function toAnthropicSchema(
+  schema: Record<string, unknown>
+): Record<string, unknown> {
+  const out = structuredClone(schema);
+
+  // Remove $schema if present
+  delete out.$schema;
+
+  // Add additionalProperties: false to objects
+  if (out.type === 'object') {
+    out.additionalProperties = false;
+  }
+
+  // Recursively process nested objects
+  for (const key in out) {
+    if (typeof out[key] === 'object' && out[key] !== null) {
+      out[key] = toAnthropicSchema(out[key] as Record<string, unknown>);
+    }
+  }
+
+  return out;
+}
+
 const unsupportedServerToolError = (blockType: string): string =>
   `Anthropic beta runner does not yet support server-managed tool block '${blockType}'. Please retry against the stable API or wait for dedicated support.`;
 
@@ -254,6 +305,7 @@ export class BetaRunner extends BaseRunner<BetaRunnerTypes> {
       max_tokens:
         request.config?.maxOutputTokens ?? this.DEFAULT_MAX_OUTPUT_TOKENS,
       messages,
+      betas: BETA_APIS,
     };
 
     if (betaSystem !== undefined) body.system = betaSystem;
@@ -281,10 +333,12 @@ export class BetaRunner extends BaseRunner<BetaRunnerTypes> {
       body.thinking = thinkingConfig as BetaMessageCreateParams['thinking'];
     }
 
-    if (request.output?.format && request.output.format !== 'text') {
-      throw new Error(
-        `Only text output format is supported for Claude models currently`
-      );
+    // Apply structured output when model supports it and constrained output is requested
+    if (this.isStructuredOutputEnabled(request)) {
+      body.output_format = {
+        type: 'json_schema',
+        schema: toAnthropicSchema(request.output!.schema!),
+      };
     }
 
     return body;
@@ -322,6 +376,7 @@ export class BetaRunner extends BaseRunner<BetaRunnerTypes> {
         request.config?.maxOutputTokens ?? this.DEFAULT_MAX_OUTPUT_TOKENS,
       messages,
       stream: true,
+      betas: BETA_APIS,
     };
 
     if (betaSystem !== undefined) body.system = betaSystem;
@@ -349,12 +404,13 @@ export class BetaRunner extends BaseRunner<BetaRunnerTypes> {
       body.thinking = thinkingConfig as BetaMessageCreateParams['thinking'];
     }
 
-    if (request.output?.format && request.output.format !== 'text') {
-      throw new Error(
-        `Only text output format is supported for Claude models currently`
-      );
+    // Apply structured output when model supports it and constrained output is requested
+    if (this.isStructuredOutputEnabled(request)) {
+      body.output_format = {
+        type: 'json_schema',
+        schema: toAnthropicSchema(request.output!.schema!),
+      };
     }
-
     return body;
   }
 
@@ -491,4 +547,14 @@ export class BetaRunner extends BaseRunner<BetaRunnerTypes> {
         return 'other';
     }
   }
+
+  private isStructuredOutputEnabled(
+    request: GenerateRequest<typeof AnthropicConfigSchema>
+  ): boolean {
+    return !!(
+      request.output?.schema &&
+      request.output.constrained &&
+      request.output.format === 'json'
+    );
+  }
 }

js/plugins/anthropic/tests/live_test.ts

@@ -22,7 +22,7 @@
  */
 
 import * as assert from 'assert';
-import { genkit } from 'genkit';
+import { genkit, z } from 'genkit';
 import { describe, it } from 'node:test';
 import { anthropic } from '../src/index.js';
 
@@ -80,4 +80,50 @@ describe('Live Anthropic API Tests', { skip: !API_KEY }, () => {
 
     assert.ok(result.text.toLowerCase().includes('hello'));
   });
+
+  it('should return structured output matching the schema', async () => {
+    const ai = genkit({
+      plugins: [anthropic({ apiKey: API_KEY, apiVersion: 'beta' })],
+    });
+
+    const schema = z.object({
+      name: z.string(),
+      age: z.number(),
+      city: z.string(),
+      isStudent: z.boolean(),
+      isEmployee: z.boolean(),
+      isRetired: z.boolean(),
+      isUnemployed: z.boolean(),
+      isDisabled: z.boolean(),
+    });
+
+    const result = await ai.generate({
+      model: 'anthropic/claude-sonnet-4-5',
+      prompt:
+        'Generate a fictional person with name "Alice", age 30, and city "New York". Return only the JSON.',
+      output: { schema, format: 'json', constrained: true },
+    });
+
+    const parsed = result.output;
+    assert.ok(parsed, 'Should have parsed output');
+    assert.deepStrictEqual(
+      { name: parsed.name, age: parsed.age, city: parsed.city },
+      { name: 'Alice', age: 30, city: 'New York' }
+    );
+
+    // Check that boolean fields are present and are actually booleans
+    for (const key of [
+      'isStudent',
+      'isEmployee',
+      'isRetired',
+      'isUnemployed',
+      'isDisabled',
+    ]) {
+      assert.strictEqual(
+        typeof parsed[key],
+        'boolean',
+        `Field ${key} should be a boolean but got: ${typeof parsed[key]}`
+      );
+    }
+  });
 });

js/plugins/anthropic/tests/mocks/anthropic-client.ts

@@ -379,7 +379,7 @@ function toBetaMessage(message: Message): BetaMessage {
       server_tool_use: message.usage.server_tool_use as any,
       service_tier: message.usage.service_tier,
     },
-  };
+  } as BetaMessage;
 }
 
 function toBetaStreamEvent(