diff --git a/internal/agent/coordinator.go b/internal/agent/coordinator.go
index 86ca09e3bf..f45fd209b5 100644
--- a/internal/agent/coordinator.go
+++ b/internal/agent/coordinator.go
@@ -948,7 +948,7 @@ func (c *coordinator) buildGoogleProvider(baseURL, apiKey string, headers map[st
 	return google.New(opts...)
 }
 
-func (c *coordinator) buildGoogleVertexProvider(headers map[string]string, options map[string]string) (fantasy.Provider, error) {
+func (c *coordinator) buildGoogleVertexProvider(baseURL, apiKey string, headers map[string]string, options map[string]string) (fantasy.Provider, error) {
 	opts := []google.Option{}
 	if c.cfg.Config().Options.Debug {
 		httpClient := log.NewHTTPClient()
@@ -961,7 +961,16 @@ func (c *coordinator) buildGoogleVertexProvider(headers map[string]string, optio
 	project := options["project"]
 	location := options["location"]
 
-	opts = append(opts, google.WithVertex(project, location))
+	if project != "" && location != "" {
+		opts = append(opts, google.WithVertex(project, location))
+	} else {
+		// Without native GCP credentials, authenticate with the configured
+		// API key (e.g. against a Gemini-API-compatible proxy).
+		opts = append(opts, google.WithGeminiAPIKey(apiKey))
+	}
+	if baseURL != "" {
+		opts = append(opts, google.WithBaseURL(baseURL))
+	}
 
 	return google.New(opts...)
 }
@@ -1016,7 +1025,7 @@ func (c *coordinator) buildProvider(providerCfg config.ProviderConfig, model con
 	case google.Name:
 		return c.buildGoogleProvider(baseURL, apiKey, headers)
 	case "google-vertex":
-		return c.buildGoogleVertexProvider(headers, providerCfg.ExtraParams)
+		return c.buildGoogleVertexProvider(baseURL, apiKey, headers, providerCfg.ExtraParams)
 	case openaicompat.Name, hyper.Name:
 		switch providerCfg.ID {
 		case hyper.Name:
diff --git a/internal/config/load.go b/internal/config/load.go
index 2f0946e7bc..bf4cc68fa6 100644
--- a/internal/config/load.go
+++ b/internal/config/load.go
@@ -284,15 +284,19 @@ func (c *Config) configureProviders(store *ConfigStore, env env.Env, resolver Va
 				project  = env.Get("VERTEXAI_PROJECT")
 				location = env.Get("VERTEXAI_LOCATION")
 			)
-			if project == "" || location == "" {
+			if project != "" && location != "" {
+				prepared.ExtraParams["project"] = project
+				prepared.ExtraParams["location"] = location
+			} else if v, err := resolver.ResolveValue(p.APIKey); v == "" || err != nil {
+				// Without native GCP credentials an API key works like any
+				// other provider (e.g. against a Gemini-API-compatible
+				// proxy); only drop the provider when neither is available.
 				if configExists {
 					slog.Warn("Skipping Vertex AI provider due to missing credentials")
 					c.Providers.Del(string(p.ID))
 				}
 				continue
 			}
-			prepared.ExtraParams["project"] = project
-			prepared.ExtraParams["location"] = location
 		case catwalk.InferenceProviderAzure:
 			endpoint, err := resolver.ResolveValue(p.APIEndpoint)
 			if err != nil || endpoint == "" {
diff --git a/internal/config/load_test.go b/internal/config/load_test.go
index 9d67acaeec..e6d2678c67 100644
--- a/internal/config/load_test.go
+++ b/internal/config/load_test.go
@@ -552,6 +552,47 @@ func TestConfig_configureProvidersVertexAIMissingProject(t *testing.T) {
 	require.Equal(t, cfg.Providers.Len(), 0)
 }
 
+// TestConfig_configureProvidersVertexAIWithAPIKey is a regression test for
+// issue #3074: a Vertex AI provider configured with an api_key (and a custom
+// base_url pointing at a proxy) used to be dropped during config load because
+// the vertexai branch only looked at the VERTEXAI_PROJECT / VERTEXAI_LOCATION
+// env vars and ignored the configured api_key entirely. Once dropped, Crush
+// thought the provider was unconfigured and prompted the user for an API key,
+// even though the same api_key style works for openai/anthropic.
+//
+// With the fix, an api_key keeps the provider alive when the GCP env vars are
+// absent, matching the generic-provider behavior.
+func TestConfig_configureProvidersVertexAIWithAPIKey(t *testing.T) {
+	knownProviders := []catwalk.Provider{
+		{
+			ID:          catwalk.InferenceProviderVertexAI,
+			APIKey:      "test-api-key",                     // user configured an api_key
+			APIEndpoint: "https://vertex-proxy.example.com", // custom proxy base_url
+			Models: []catwalk.Model{{
+				ID: "gemini-pro",
+			}},
+		},
+	}
+
+	cfg := &Config{}
+	cfg.setDefaults("/tmp", "")
+	// No VERTEXAI_PROJECT / VERTEXAI_LOCATION on purpose: the user is
+	// authenticating via api_key + proxy, not native GCP credentials.
+	env := env.NewFromMap(map[string]string{})
+	resolver := NewShellVariableResolver(env)
+	err := cfg.configureProviders(testStore(cfg), env, resolver, knownProviders)
+	require.NoError(t, err)
+	require.Equal(t, 1, cfg.Providers.Len(),
+		"vertexai provider with an api_key must be kept (issue #3074)")
+
+	vertexProvider, ok := cfg.Providers.Get("vertexai")
+	require.True(t, ok, "VertexAI provider should be present")
+	require.Equal(t, "test-api-key", vertexProvider.APIKey)
+	require.Equal(t, "https://vertex-proxy.example.com", vertexProvider.BaseURL)
+	require.Empty(t, vertexProvider.ExtraParams["project"], "no GCP project expected when authenticating via api_key")
+	require.Empty(t, vertexProvider.ExtraParams["location"])
+}
+
 func TestConfig_configureProvidersSetProviderID(t *testing.T) {
 	knownProviders := []catwalk.Provider{
 		{