diff --git a/containers/api-proxy/server.js b/containers/api-proxy/server.js
index 2819d672b..181aa0d23 100644
--- a/containers/api-proxy/server.js
+++ b/containers/api-proxy/server.js
@@ -10,6 +10,8 @@
  * 4. Respects domain whitelisting enforced by Squid
  */
 
+const fs = require('fs');
+const path = require('path');
 const http = require('http');
 const https = require('https');
 const tls = require('tls');
@@ -1424,6 +1426,74 @@ async function fetchStartupModels(overrides = {}) {
   modelFetchComplete = true;
 }
 
+// Default log directory for models.json (matches the volume mount in docker-compose)
+const MODELS_LOG_DIR = process.env.AWF_API_PROXY_LOG_DIR || '/var/log/api-proxy';
+
+/**
+ * Build the models.json payload from current cached state.
+ *
+ * @returns {object} The models JSON object with timestamp, providers, and model_aliases
+ */
+function buildModelsJson() {
+  const opencodeConfigured = !!(OPENAI_API_KEY || ANTHROPIC_API_KEY || COPILOT_AUTH_TOKEN);
+  return {
+    timestamp: new Date().toISOString(),
+    providers: {
+      openai: {
+        configured: !!OPENAI_API_KEY,
+        models: cachedModels.openai !== undefined ? cachedModels.openai : null,
+        target: OPENAI_API_KEY ? OPENAI_API_TARGET : null,
+      },
+      anthropic: {
+        configured: !!ANTHROPIC_API_KEY,
+        models: cachedModels.anthropic !== undefined ? cachedModels.anthropic : null,
+        target: ANTHROPIC_API_KEY ? ANTHROPIC_API_TARGET : null,
+      },
+      copilot: {
+        configured: !!COPILOT_AUTH_TOKEN,
+        models: cachedModels.copilot !== undefined ? cachedModels.copilot : null,
+        target: COPILOT_AUTH_TOKEN ? COPILOT_API_TARGET : null,
+      },
+      gemini: {
+        configured: !!GEMINI_API_KEY,
+        models: cachedModels.gemini !== undefined ? cachedModels.gemini : null,
+        target: GEMINI_API_KEY ? GEMINI_API_TARGET : null,
+      },
+      opencode: {
+        configured: opencodeConfigured,
+        models: null,
+        target: null,
+      },
+    },
+    model_aliases: MODEL_ALIASES ? MODEL_ALIASES.models : null,
+  };
+}
+
+/**
+ * Write the current model availability snapshot to models.json in the log directory.
+ *
+ * Called after fetchStartupModels() completes.
+ * The file is written to the volume-mounted log directory so it is automatically
+ * available for artifact upload.
+ *
+ * @param {string} [logDir] - Directory to write models.json to (default: MODELS_LOG_DIR)
+ */
+function writeModelsJson(logDir = MODELS_LOG_DIR) {
+  const filePath = path.join(logDir, 'models.json');
+  try {
+    fs.mkdirSync(logDir, { recursive: true });
+    fs.writeFileSync(filePath, JSON.stringify(buildModelsJson(), null, 2) + '\n', 'utf8');
+    logRequest('info', 'models_json_written', { path: filePath });
+  } catch (err) {
+    logRequest('warn', 'models_json_write_failed', {
+      message: 'Failed to write models.json',
+      logDir,
+      path: filePath,
+      error: err instanceof Error ? (err.stack || err.message) : String(err),
+    });
+  }
+}
+
 /**
  * Build the reflection response describing all proxy endpoints and their available models.
  *
@@ -1550,9 +1620,12 @@ if (require.main === module) {
         logRequest('error', 'key_validation_error', { message: 'Unexpected error during key validation', error: String(err) });
         keyValidationComplete = true;
       });
-      fetchStartupModels().catch((err) => {
+      fetchStartupModels().then(() => {
+        writeModelsJson();
+      }).catch((err) => {
         logRequest('error', 'model_fetch_error', { message: 'Unexpected error fetching startup models', error: String(err) });
         modelFetchComplete = true;
+        writeModelsJson();
       });
     }
   }
@@ -1855,4 +1928,4 @@ if (require.main === module) {
 }
 
 // Export for testing
-module.exports = { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute, shouldStripHeader, stripGeminiKeyParam, validateApiKeys, probeProvider, httpProbe, keyValidationResults, resetKeyValidationState, fetchJson, extractModelIds, fetchStartupModels, reflectEndpoints, healthResponse, cachedModels, resetModelCacheState, makeModelBodyTransform, MODEL_ALIASES };
+module.exports = { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute, shouldStripHeader, stripGeminiKeyParam, validateApiKeys, probeProvider, httpProbe, keyValidationResults, resetKeyValidationState, fetchJson, extractModelIds, fetchStartupModels, reflectEndpoints, healthResponse, cachedModels, resetModelCacheState, makeModelBodyTransform, MODEL_ALIASES, buildModelsJson, writeModelsJson };
diff --git a/containers/api-proxy/server.test.js b/containers/api-proxy/server.test.js
index f5c36244f..1d254e9d3 100644
--- a/containers/api-proxy/server.test.js
+++ b/containers/api-proxy/server.test.js
@@ -6,7 +6,7 @@ const http = require('http');
 const https = require('https');
 const tls = require('tls');
 const { EventEmitter } = require('events');
-const { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute, shouldStripHeader, stripGeminiKeyParam, httpProbe, validateApiKeys, keyValidationResults, resetKeyValidationState, fetchJson, extractModelIds, fetchStartupModels, reflectEndpoints, healthResponse, cachedModels, resetModelCacheState, makeModelBodyTransform, MODEL_ALIASES } = require('./server');
+const { normalizeApiTarget, deriveCopilotApiTarget, deriveGitHubApiTarget, deriveGitHubApiBasePath, normalizeBasePath, buildUpstreamPath, proxyWebSocket, resolveCopilotAuthToken, resolveOpenCodeRoute, shouldStripHeader, stripGeminiKeyParam, httpProbe, validateApiKeys, keyValidationResults, resetKeyValidationState, fetchJson, extractModelIds, fetchStartupModels, reflectEndpoints, healthResponse, cachedModels, resetModelCacheState, makeModelBodyTransform, MODEL_ALIASES, buildModelsJson, writeModelsJson } = require('./server');
 
 describe('normalizeApiTarget', () => {
   it('should strip https:// prefix', () => {
@@ -1787,3 +1787,132 @@ describe('makeModelBodyTransform', () => {
   });
 });
 
+// ── buildModelsJson ────────────────────────────────────────────────────────
+
+describe('buildModelsJson', () => {
+  afterEach(() => {
+    resetModelCacheState();
+  });
+
+  it('should return an object with timestamp, providers, and model_aliases fields', () => {
+    const result = buildModelsJson();
+    expect(typeof result.timestamp).toBe('string');
+    expect(typeof result.providers).toBe('object');
+    expect(result).toHaveProperty('model_aliases');
+  });
+
+  it('should include all five providers', () => {
+    const result = buildModelsJson();
+    const providerKeys = Object.keys(result.providers);
+    expect(providerKeys).toHaveLength(5);
+    expect(providerKeys).toEqual(expect.arrayContaining(['openai', 'anthropic', 'copilot', 'gemini', 'opencode']));
+  });
+
+  it('should set models to null for uncached providers', () => {
+    const result = buildModelsJson();
+    // Without populating cachedModels, all models fields should be null
+    for (const provider of ['openai', 'anthropic', 'copilot', 'gemini', 'opencode']) {
+      expect(result.providers[provider].models).toBeNull();
+    }
+  });
+
+  it('should include cached models when available', () => {
+    cachedModels.openai = ['gpt-4o', 'gpt-4o-mini'];
+    cachedModels.copilot = ['claude-sonnet-4'];
+    const result = buildModelsJson();
+    expect(result.providers.openai.models).toEqual(['gpt-4o', 'gpt-4o-mini']);
+    expect(result.providers.copilot.models).toEqual(['claude-sonnet-4']);
+    expect(result.providers.anthropic.models).toBeNull();
+  });
+
+  it('should include null models for providers that returned null (fetch failed)', () => {
+    cachedModels.openai = null;
+    const result = buildModelsJson();
+    expect(result.providers.openai.models).toBeNull();
+  });
+
+  it('should set model_aliases to null when MODEL_ALIASES is not configured', () => {
+    // MODEL_ALIASES is a module-level constant fixed at import time.
+    // This assertion is only meaningful when AWF_MODEL_ALIASES is unset.
+    if (MODEL_ALIASES) {
+      expect(MODEL_ALIASES).not.toBeNull(); // trivially passes — env var is set, skip
+      return;
+    }
+    const result = buildModelsJson();
+    expect(result.model_aliases).toBeNull();
+  });
+
+  it('should produce a valid ISO 8601 timestamp', () => {
+    const result = buildModelsJson();
+    const ts = new Date(result.timestamp);
+    expect(ts.toString()).not.toBe('Invalid Date');
+  });
+
+  it('should include opencode provider with correct static fields', () => {
+    // opencode.configured mirrors whether any base provider is configured at
+    // module load time — just verify the expected shape is always present.
+    const result = buildModelsJson();
+    expect(typeof result.providers.opencode.configured).toBe('boolean');
+    expect(result.providers.opencode.models).toBeNull();
+    expect(result.providers.opencode.target).toBeNull();
+  });
+});
+
+// ── writeModelsJson ────────────────────────────────────────────────────────
+
+describe('writeModelsJson', () => {
+  const os = require('os');
+  const fs = require('fs');
+  const path = require('path');
+
+  let tmpDir;
+
+  beforeEach(() => {
+    resetModelCacheState();
+    tmpDir = fs.mkdtempSync(path.join(os.tmpdir(), 'awf-test-models-'));
+  });
+
+  afterEach(() => {
+    resetModelCacheState();
+    try { fs.rmSync(tmpDir, { recursive: true, force: true }); } catch { /* ignore */ }
+  });
+
+  it('should write models.json to the specified directory', () => {
+    writeModelsJson(tmpDir);
+    const filePath = path.join(tmpDir, 'models.json');
+    expect(fs.existsSync(filePath)).toBe(true);
+  });
+
+  it('should write valid JSON', () => {
+    writeModelsJson(tmpDir);
+    const content = fs.readFileSync(path.join(tmpDir, 'models.json'), 'utf8');
+    expect(() => JSON.parse(content)).not.toThrow();
+  });
+
+  it('should write JSON with the expected schema', () => {
+    cachedModels.openai = ['gpt-4o'];
+    writeModelsJson(tmpDir);
+    const data = JSON.parse(fs.readFileSync(path.join(tmpDir, 'models.json'), 'utf8'));
+    expect(typeof data.timestamp).toBe('string');
+    expect(typeof data.providers).toBe('object');
+    const providerKeys = Object.keys(data.providers);
+    expect(providerKeys).toHaveLength(5);
+    expect(providerKeys).toEqual(expect.arrayContaining(['openai', 'anthropic', 'copilot', 'gemini', 'opencode']));
+    expect(data).toHaveProperty('model_aliases');
+  });
+
+  it('should create the directory if it does not exist', () => {
+    const nestedDir = path.join(tmpDir, 'sub', 'dir');
+    writeModelsJson(nestedDir);
+    expect(fs.existsSync(path.join(nestedDir, 'models.json'))).toBe(true);
+  });
+
+  it('should overwrite an existing models.json on subsequent writes', () => {
+    writeModelsJson(tmpDir);
+    cachedModels.copilot = ['claude-sonnet-4'];
+    writeModelsJson(tmpDir);
+    const data = JSON.parse(fs.readFileSync(path.join(tmpDir, 'models.json'), 'utf8'));
+    expect(data.providers.copilot.models).toEqual(['claude-sonnet-4']);
+  });
+});
+