diff --git a/src/trace-api.js b/src/trace-api.js
index 2fc11542f..db8844830 100644
--- a/src/trace-api.js
+++ b/src/trace-api.js
@@ -36,9 +36,10 @@ var ROOT_SPAN_STACK_OFFSET = semver.satisfies(process.version, '>=8') ? 0 : 2;
 var phantomApiImpl = {
   enhancedDatabaseReportingEnabled: function() { return false; },
   runInRootSpan: function(opts, fn) { return fn(null); },
-  getCurrentContext: function() { return null; },
+  getCurrentContextId: function() { return null; },
   createChildSpan: function(opts) { return null; },
   getResponseTraceContext: function(context, traced) { return ''; },
+  getWriterProjectId : function() { return null; },
   wrap: function(fn) { return fn; },
   wrapEmitter: function(ee) {},
 };
@@ -196,6 +197,15 @@ TraceAgent.prototype.getCurrentContextId = function() {
   return rootSpan.trace.traceId;
 };
 
+/**
+ * Returns the projectId that was either configured or auto-discovered by the
+ * TraceWriter. Note that the auto-discovery is done asynchronously, so this
+ * may return falsey until the projectId auto-discovery completes.
+ */
+TraceAgent.prototype.getWriterProjectId = function() {
+  return this.config_.projectId;
+};
+
 /**
  * Creates and returns a new ChildSpan object nested within the root span. If
  * there is no current RootSpan object, this function returns null.
diff --git a/test/test-index.js b/test/test-index.js
index d563fc69e..672c3a1cc 100644
--- a/test/test-index.js
+++ b/test/test-index.js
@@ -19,6 +19,7 @@
 require('./plugins/common.js');
 var assert = require('assert');
 var nock = require('nock');
+var nocks = require('./nocks.js');
 var trace = require('..');
 var TraceAgent = require('../src/trace-api.js');
 
@@ -78,4 +79,21 @@ describe('index.js', function() {
       done();
     }, 500);
   });
+
+  it('should allow project ID to be read after discovery', function(done) {
+    var envProjectId = process.env.GCLOUD_PROJECT;
+    delete process.env.GCLOUD_PROJECT;
+
+    nocks.projectId(function() { return 'project1'; });
+    nocks.hostname(function() { return 'host1'; });
+    nocks.instanceId(function() { return 'instance1'; });
+
+    var agent = trace.start({logLevel: 0, forceNewAgent_: true});
+
+    setTimeout(function() {
+      assert.strictEqual(agent.getWriterProjectId(), 'project1');
+      process.env.GCLOUD_PROJECT = envProjectId;
+      done();
+    }, 500);
+  });
 });
diff --git a/test/test-trace-api.js b/test/test-trace-api.js
index cccd9adc5..9d53deade 100644
--- a/test/test-trace-api.js
+++ b/test/test-trace-api.js
@@ -49,6 +49,7 @@ function assertAPISurface(traceAPI) {
     }
   });
   assert.strictEqual(typeof traceAPI.getCurrentContextId, 'function');
+  assert.strictEqual(typeof traceAPI.getWriterProjectId, 'function');
   var child = traceAPI.createChildSpan({ name: 'child' });
   // TODO: Ditto but with child spans
   if (child) {
@@ -180,7 +181,13 @@ describe('Trace Interface', function() {
       traceAPI.runInRootSpan({name: 'root', url: 'root'}, function(rootSpan) {
         var id = traceAPI.getCurrentContextId();
         assert.strictEqual(id, rootSpan.trace.traceId);
-      });      
+      });
+    });
+
+    it('should return get the project ID if set in config', function() {
+      var config = {projectId: 'project-1'};
+      var traceApi = createTraceAgent(null /* policy */, config);
+      assert.equal(traceApi.getWriterProjectId(), 'project-1');
     });
 
     it('should add labels to spans', function() {