diff --git a/main.go b/main.go
index a20ae55..9f85343 100644
--- a/main.go
+++ b/main.go
@@ -107,8 +107,8 @@ func queryModelsContextWindow(cfg *Cfg) int {
   req.Header.Set("User-Agent", opencodeAgentVersion)
   req.Header.Set("X-Session-Id", projectID())
   req.Header.Set("x-opencode-project", projectID())
-  req.Header.Set("x-opencode-client", opencodeAgentVersion)
-  req.Header.Set("x-opencode-session", projectID())
+  req.Header.Set("x-opencode-client", "cli")
+  req.Header.Set("x-opencode-session", opencodeSessionID())
   if cfg.APIKey != "" && cfg.APIKey != "-" { req.Header.Set("Authorization", "Bearer "+cfg.APIKey) }
   resp, err := client.Do(req)
   if err != nil || resp.StatusCode >= 400 { return 0 }
@@ -183,8 +183,8 @@ func listModels(cfg *Cfg) (string, error) {
   req.Header.Set("User-Agent", opencodeAgentVersion)
   req.Header.Set("X-Session-Id", projectID())
   req.Header.Set("x-opencode-project", projectID())
-  req.Header.Set("x-opencode-client", opencodeAgentVersion)
-  req.Header.Set("x-opencode-session", projectID())
+  req.Header.Set("x-opencode-client", "cli")
+  req.Header.Set("x-opencode-session", opencodeSessionID())
   if cfg.APIKey != "" && cfg.APIKey != "-" { req.Header.Set("Authorization", "Bearer "+cfg.APIKey) }
   resp, err := client.Do(req)
   if err != nil { return "", err }
@@ -1055,8 +1055,8 @@ func llm(ctx context.Context, cfg *Cfg, msgs []Message, tools []map[string]any)
     req.Header.Set("User-Agent", opencodeAgentVersion)
     req.Header.Set("X-Session-Id", projectID())
     req.Header.Set("x-opencode-project", projectID())
-    req.Header.Set("x-opencode-client", opencodeAgentVersion)
-    req.Header.Set("x-opencode-session", projectID())
+    req.Header.Set("x-opencode-client", "cli")
+    req.Header.Set("x-opencode-session", opencodeSessionID())
     if cfg.APIKey != "" && cfg.APIKey != "-" { req.Header.Set("Authorization", "Bearer "+cfg.APIKey) }
     resp, err = client.Do(req)
     var is4xxClientErr bool
@@ -1621,6 +1621,16 @@ func projectID() string {
   return hex.EncodeToString(h[:])
 }
 
+func opencodeSessionID() string {
+  pid := projectID()
+  if len(pid) > 26 {
+    pid = pid[:26]
+  } else if len(pid) < 26 {
+    pid = (pid + "0123456789abcdef0123456789")[:26]
+  }
+  return "ses_" + pid
+}
+
 func saveSession(msgs []Message, sid string) (string, string) {
   sid = strings.TrimSpace(sid)
   if sid == "" {
diff --git a/main_test.go b/main_test.go
index cb2c7d1..6350173 100644
--- a/main_test.go
+++ b/main_test.go
@@ -1147,11 +1147,13 @@ func TestCol(t *testing.T) {
 // ---------- llm / AL / summarize / compact via httptest (no real network) ----------
 
 func TestLLMNonStreamingAndHeaders(t *testing.T) {
-  var gotPath, gotAuth, gotUA string
+  var gotPath, gotAuth, gotUA, gotOCClient, gotOCSession string
   srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
     gotPath = r.URL.Path
     gotAuth = r.Header.Get("Authorization")
     gotUA = r.Header.Get("User-Agent")
+    gotOCClient = r.Header.Get("x-opencode-client")
+    gotOCSession = r.Header.Get("x-opencode-session")
     w.Write([]byte(`{"choices":[{"message":{"role":"assistant","content":"hi","reasoning_content":"think"}}]}`))
   }))
   defer srv.Close()
@@ -1173,11 +1175,32 @@ func TestLLMNonStreamingAndHeaders(t *testing.T) {
   if !strings.Contains(gotUA, "opencode/1.18.31") {
     t.Errorf("user-agent = %q", gotUA)
   }
+  if gotOCClient != "cli" {
+    t.Errorf("x-opencode-client = %q, want cli", gotOCClient)
+  }
+  if gotOCSession != opencodeSessionID() {
+    t.Errorf("x-opencode-session = %q, want %q", gotOCSession, opencodeSessionID())
+  }
   if m.Content == nil || *m.Content != "hi" || m.ReasoningContent != "think" {
     t.Errorf("message = %+v", m)
   }
 }
 
+func TestOpencodeSessionID(t *testing.T) {
+  sid := opencodeSessionID()
+  if !strings.HasPrefix(sid, "ses_") {
+    t.Fatalf("session id does not start with ses_: %q", sid)
+  }
+  if len(sid) != 30 {
+    t.Fatalf("session id length = %d, want 30: %q", len(sid), sid)
+  }
+  for _, c := range sid[4:] {
+    if !((c >= '0' && c <= '9') || (c >= 'a' && c <= 'z') || (c >= 'A' && c <= 'Z')) {
+      t.Fatalf("invalid character %c in session id %q", c, sid)
+    }
+  }
+}
+
 func TestLLMNoAuthHeaderWhenNoKey(t *testing.T) {
   var gotAuth string
   srv := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {