diff --git a/README.md b/README.md
index de6fc06..2de88f5 100644
--- a/README.md
+++ b/README.md
@@ -60,12 +60,17 @@ or compact `system` / `user` fields. The completed job result contains
 - `GET /healthz` returns process health.
 - `GET /readyz` checks PostgreSQL readiness.
 
+All `/api/v1/*` endpoints require `Authorization: Bearer <AI_SERVICE_TOKEN>`
+when `AI_SERVICE_TOKEN` is configured. Health and readiness endpoints stay open
+for Kubernetes probes.
+
 ## Configuration
 
 - `HTTP_HOST`, default `0.0.0.0`
 - `HTTP_PORT`, default `8080`
 - `DATABASE_URL`, required
 - `MIGRATE_ON_START`, default `true`
+- `AI_SERVICE_TOKEN`, optional bearer token for service-to-service API calls
 - `LLM_BASE_URL`, primary OpenAI-compatible LLM endpoint
 - `LLM_API_KEY`, primary LLM API key
 - `LLM_MODEL`, default `qwen2.5-14b`
diff --git a/internal/config/config.go b/internal/config/config.go
index 284e7b8..fadad08 100644
--- a/internal/config/config.go
+++ b/internal/config/config.go
@@ -11,6 +11,7 @@ type Config struct {
 	HTTPPort       int
 	DatabaseURL    string
 	MigrateOnStart bool
+	APIAuthToken   string
 
 	LLMBaseURL  string
 	LLMAPIKey   string
@@ -30,6 +31,7 @@ func Load() Config {
 		HTTPPort:       envInt("HTTP_PORT", 8080),
 		DatabaseURL:    envString("DATABASE_URL", ""),
 		MigrateOnStart: envBool("MIGRATE_ON_START", true),
+		APIAuthToken:   envString("AI_SERVICE_TOKEN", ""),
 
 		LLMBaseURL:  envString("LLM_BASE_URL", ""),
 		LLMAPIKey:   envString("LLM_API_KEY", ""),
diff --git a/internal/httpapi/auth.go b/internal/httpapi/auth.go
new file mode 100644
index 0000000..b088beb
--- /dev/null
+++ b/internal/httpapi/auth.go
@@ -0,0 +1,30 @@
+package httpapi
+
+import (
+	"crypto/subtle"
+	"net/http"
+	"strings"
+)
+
+func (s *Server) requireAPIToken(path string, r *http.Request) bool {
+	if !strings.HasPrefix(path, "/api/v1/") && path != "/api/v1" {
+		return true
+	}
+	expected := strings.TrimSpace(s.cfg.APIAuthToken)
+	if expected == "" {
+		return true
+	}
+	got := bearerToken(r.Header.Get("Authorization"))
+	if got == "" {
+		return false
+	}
+	return subtle.ConstantTimeCompare([]byte(got), []byte(expected)) == 1
+}
+
+func bearerToken(header string) string {
+	header = strings.TrimSpace(header)
+	if len(header) < len("Bearer ") || !strings.EqualFold(header[:len("Bearer ")], "Bearer ") {
+		return ""
+	}
+	return strings.TrimSpace(header[len("Bearer "):])
+}
diff --git a/internal/httpapi/auth_test.go b/internal/httpapi/auth_test.go
new file mode 100644
index 0000000..81af410
--- /dev/null
+++ b/internal/httpapi/auth_test.go
@@ -0,0 +1,47 @@
+package httpapi
+
+import (
+	"net/http"
+	"net/http/httptest"
+	"testing"
+
+	"ai-service/internal/config"
+)
+
+func TestAPITokenProtectsAPIRoutes(t *testing.T) {
+	srv := NewServer(nil, config.Config{APIAuthToken: "secret"})
+
+	req := httptest.NewRequest(http.MethodGet, "/api/v1/stats", nil)
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("expected unauthorized API request to be 401, got %d", rec.Code)
+	}
+
+	req = httptest.NewRequest(http.MethodGet, "/api/v1/not-found", nil)
+	req.Header.Set("Authorization", "Bearer wrong")
+	rec = httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusUnauthorized {
+		t.Fatalf("expected wrong token to be 401, got %d", rec.Code)
+	}
+
+	req = httptest.NewRequest(http.MethodGet, "/api/v1/not-found", nil)
+	req.Header.Set("Authorization", "Bearer secret")
+	rec = httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusNotFound {
+		t.Fatalf("expected authorized unknown route to be 404, got %d", rec.Code)
+	}
+}
+
+func TestAPITokenDoesNotProtectHealth(t *testing.T) {
+	srv := NewServer(nil, config.Config{APIAuthToken: "secret"})
+
+	req := httptest.NewRequest(http.MethodGet, "/healthz", nil)
+	rec := httptest.NewRecorder()
+	srv.ServeHTTP(rec, req)
+	if rec.Code != http.StatusOK {
+		t.Fatalf("expected healthz to stay open, got %d", rec.Code)
+	}
+}
diff --git a/internal/httpapi/server.go b/internal/httpapi/server.go
index 570bd1a..58cb5e8 100644
--- a/internal/httpapi/server.go
+++ b/internal/httpapi/server.go
@@ -29,6 +29,10 @@ func (s *Server) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	if path == "" {
 		path = "/"
 	}
+	if !s.requireAPIToken(path, r) {
+		writeError(w, http.StatusUnauthorized, "unauthorized")
+		return
+	}
 	switch {
 	case r.Method == http.MethodGet && path == "/healthz":
 		writeJSON(w, http.StatusOK, map[string]string{"status": "ok"})
diff --git a/k8s/secrets.yaml b/k8s/secrets.yaml
index 41b1a07..3680a8c 100644
--- a/k8s/secrets.yaml
+++ b/k8s/secrets.yaml
@@ -18,3 +18,4 @@ type: Opaque
 stringData:
   DATABASE_URL: "postgres://ai_service:ai_service@postgres:5432/ai_service?sslmode=disable"
   LLM_API_KEY: "sk-111f838ccec43406e078cd9094b6797307cb895236179f32"
+  AI_SERVICE_TOKEN: "d18bcacf9e02bae1806ee6b6eeda62b95be6a915c0a22936d9a700128b275442"