diff --git a/.env.example b/.env.example
index 4cbd157..6dc4b70 100644
--- a/.env.example
+++ b/.env.example
@@ -62,9 +62,15 @@ OTEL_SERVICE_NAME=mosaic-gateway
 # Comma-separated list of Ollama model IDs to register (default: llama3.2,codellama,mistral)
 # OLLAMA_MODELS=llama3.2,codellama,mistral
 
-# OpenAI — required for embedding and log-summarization features
+# Anthropic (claude-sonnet-4-6, claude-opus-4-6, claude-haiku-4-5)
+# ANTHROPIC_API_KEY=sk-ant-...
+
+# OpenAI (gpt-4o, gpt-4o-mini, o3-mini)
 # OPENAI_API_KEY=sk-...
 
+# Z.ai / GLM (glm-4.5, glm-4.5-air, glm-4.5-flash)
+# ZAI_API_KEY=...
+
 # Custom providers — JSON array of provider configs
 # Format: [{"id":"<id>","baseUrl":"<url>","apiKey":"<key>","models":[{"id":"<model-id>","name":"<label>"}]}]
 # MOSAIC_CUSTOM_PROVIDERS=
diff --git a/apps/gateway/src/agent/__tests__/provider.service.test.ts b/apps/gateway/src/agent/__tests__/provider.service.test.ts
new file mode 100644
index 0000000..d69ea88
--- /dev/null
+++ b/apps/gateway/src/agent/__tests__/provider.service.test.ts
@@ -0,0 +1,143 @@
+import { beforeEach, afterEach, describe, expect, it } from 'vitest';
+import { ProviderService } from '../provider.service.js';
+
+const ENV_KEYS = [
+  'ANTHROPIC_API_KEY',
+  'OPENAI_API_KEY',
+  'ZAI_API_KEY',
+  'OLLAMA_BASE_URL',
+  'OLLAMA_HOST',
+  'OLLAMA_MODELS',
+  'MOSAIC_CUSTOM_PROVIDERS',
+] as const;
+
+type EnvKey = (typeof ENV_KEYS)[number];
+
+describe('ProviderService', () => {
+  const savedEnv = new Map<EnvKey, string | undefined>();
+
+  beforeEach(() => {
+    for (const key of ENV_KEYS) {
+      savedEnv.set(key, process.env[key]);
+      delete process.env[key];
+    }
+  });
+
+  afterEach(() => {
+    for (const key of ENV_KEYS) {
+      const value = savedEnv.get(key);
+      if (value === undefined) {
+        delete process.env[key];
+      } else {
+        process.env[key] = value;
+      }
+    }
+  });
+
+  it('skips API-key providers when env vars are missing (no models become available)', () => {
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    // Pi's built-in registry may include model definitions for all providers, but
+    // without API keys none of them should be available (usable).
+    const availableModels = service.listAvailableModels();
+    const availableProviderIds = new Set(availableModels.map((m) => m.provider));
+
+    expect(availableProviderIds).not.toContain('anthropic');
+    expect(availableProviderIds).not.toContain('openai');
+    expect(availableProviderIds).not.toContain('zai');
+
+    // Providers list may show built-in providers, but they should not be marked available
+    const providers = service.listProviders();
+    for (const p of providers.filter((p) => ['anthropic', 'openai', 'zai'].includes(p.id))) {
+      expect(p.available).toBe(false);
+    }
+  });
+
+  it('registers Anthropic provider with correct models when ANTHROPIC_API_KEY is set', () => {
+    process.env['ANTHROPIC_API_KEY'] = 'test-anthropic';
+
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    const providers = service.listProviders();
+    const anthropic = providers.find((p) => p.id === 'anthropic');
+    expect(anthropic).toBeDefined();
+    expect(anthropic!.available).toBe(true);
+    expect(anthropic!.models.map((m) => m.id)).toEqual([
+      'claude-sonnet-4-6',
+      'claude-opus-4-6',
+      'claude-haiku-4-5',
+    ]);
+    // contextWindow override from Pi built-in (200000)
+    for (const m of anthropic!.models) {
+      expect(m.contextWindow).toBe(200000);
+      // maxTokens capped at 8192 per task spec
+      expect(m.maxTokens).toBe(8192);
+    }
+  });
+
+  it('registers OpenAI provider with correct models when OPENAI_API_KEY is set', () => {
+    process.env['OPENAI_API_KEY'] = 'test-openai';
+
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    const providers = service.listProviders();
+    const openai = providers.find((p) => p.id === 'openai');
+    expect(openai).toBeDefined();
+    expect(openai!.available).toBe(true);
+    expect(openai!.models.map((m) => m.id)).toEqual(['gpt-4o', 'gpt-4o-mini', 'o3-mini']);
+  });
+
+  it('registers Z.ai provider with correct models when ZAI_API_KEY is set', () => {
+    process.env['ZAI_API_KEY'] = 'test-zai';
+
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    const providers = service.listProviders();
+    const zai = providers.find((p) => p.id === 'zai');
+    expect(zai).toBeDefined();
+    expect(zai!.available).toBe(true);
+    expect(zai!.models.map((m) => m.id)).toEqual(['glm-4.5', 'glm-4.5-air', 'glm-4.5-flash']);
+  });
+
+  it('registers all three providers when all keys are set', () => {
+    process.env['ANTHROPIC_API_KEY'] = 'test-anthropic';
+    process.env['OPENAI_API_KEY'] = 'test-openai';
+    process.env['ZAI_API_KEY'] = 'test-zai';
+
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    const providerIds = service.listProviders().map((p) => p.id);
+    expect(providerIds).toContain('anthropic');
+    expect(providerIds).toContain('openai');
+    expect(providerIds).toContain('zai');
+  });
+
+  it('can find registered Anthropic models by provider+id', () => {
+    process.env['ANTHROPIC_API_KEY'] = 'test-anthropic';
+
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    const sonnet = service.findModel('anthropic', 'claude-sonnet-4-6');
+    expect(sonnet).toBeDefined();
+    expect(sonnet!.provider).toBe('anthropic');
+    expect(sonnet!.id).toBe('claude-sonnet-4-6');
+  });
+
+  it('can find registered Z.ai models by provider+id', () => {
+    process.env['ZAI_API_KEY'] = 'test-zai';
+
+    const service = new ProviderService();
+    service.onModuleInit();
+
+    const glm = service.findModel('zai', 'glm-4.5');
+    expect(glm).toBeDefined();
+    expect(glm!.provider).toBe('zai');
+    expect(glm!.id).toBe('glm-4.5');
+  });
+});
diff --git a/apps/gateway/src/agent/provider.service.ts b/apps/gateway/src/agent/provider.service.ts
index 255655f..36cdf0c 100644
--- a/apps/gateway/src/agent/provider.service.ts
+++ b/apps/gateway/src/agent/provider.service.ts
@@ -1,6 +1,6 @@
 import { Injectable, Logger, type OnModuleInit } from '@nestjs/common';
 import { ModelRegistry, AuthStorage } from '@mariozechner/pi-coding-agent';
-import type { Model, Api } from '@mariozechner/pi-ai';
+import { getModel, type Model, type Api } from '@mariozechner/pi-ai';
 import type { ModelInfo, ProviderInfo, CustomProviderConfig } from '@mosaic/types';
 import type { TestConnectionResultDto } from './provider.dto.js';
 
@@ -14,6 +14,9 @@ export class ProviderService implements OnModuleInit {
     this.registry = new ModelRegistry(authStorage);
 
     this.registerOllamaProvider();
+    this.registerAnthropicProvider();
+    this.registerOpenAIProvider();
+    this.registerZaiProvider();
     this.registerCustomProviders();
 
     const available = this.registry.getAvailable();
@@ -140,6 +143,66 @@ export class ProviderService implements OnModuleInit {
     this.logger.log(`Registered custom provider: ${config.id} (${config.models.length} models)`);
   }
 
+  private registerAnthropicProvider(): void {
+    const apiKey = process.env['ANTHROPIC_API_KEY'];
+    if (!apiKey) {
+      this.logger.debug('Skipping Anthropic provider registration: ANTHROPIC_API_KEY not set');
+      return;
+    }
+
+    const models = ['claude-sonnet-4-6', 'claude-opus-4-6', 'claude-haiku-4-5'].map((id) =>
+      this.cloneBuiltInModel('anthropic', id, { maxTokens: 8192 }),
+    );
+
+    this.registry.registerProvider('anthropic', {
+      apiKey,
+      baseUrl: 'https://api.anthropic.com',
+      models,
+    });
+
+    this.logger.log('Anthropic provider registered with 3 models');
+  }
+
+  private registerOpenAIProvider(): void {
+    const apiKey = process.env['OPENAI_API_KEY'];
+    if (!apiKey) {
+      this.logger.debug('Skipping OpenAI provider registration: OPENAI_API_KEY not set');
+      return;
+    }
+
+    const models = ['gpt-4o', 'gpt-4o-mini', 'o3-mini'].map((id) =>
+      this.cloneBuiltInModel('openai', id),
+    );
+
+    this.registry.registerProvider('openai', {
+      apiKey,
+      baseUrl: 'https://api.openai.com/v1',
+      models,
+    });
+
+    this.logger.log('OpenAI provider registered with 3 models');
+  }
+
+  private registerZaiProvider(): void {
+    const apiKey = process.env['ZAI_API_KEY'];
+    if (!apiKey) {
+      this.logger.debug('Skipping Z.ai provider registration: ZAI_API_KEY not set');
+      return;
+    }
+
+    const models = ['glm-4.5', 'glm-4.5-air', 'glm-4.5-flash'].map((id) =>
+      this.cloneBuiltInModel('zai', id),
+    );
+
+    this.registry.registerProvider('zai', {
+      apiKey,
+      baseUrl: 'https://open.bigmodel.cn/api/paas/v4',
+      models,
+    });
+
+    this.logger.log('Z.ai provider registered with 3 models');
+  }
+
   private registerOllamaProvider(): void {
     const ollamaUrl = process.env['OLLAMA_BASE_URL'] ?? process.env['OLLAMA_HOST'];
     if (!ollamaUrl) return;
@@ -184,6 +247,19 @@ export class ProviderService implements OnModuleInit {
     }
   }
 
+  private cloneBuiltInModel(
+    provider: string,
+    modelId: string,
+    overrides: Partial<Model<Api>> = {},
+  ): Model<Api> {
+    const model = getModel(provider as never, modelId as never) as Model<Api> | undefined;
+    if (!model) {
+      throw new Error(`Built-in model not found: ${provider}:${modelId}`);
+    }
+
+    return { ...model, ...overrides };
+  }
+
   private toModelInfo(model: Model<Api>): ModelInfo {
     return {
       id: model.id,