diff --git a/aibridge/session.go b/aibridge/session.go
index 9882029ea3..dcd60ed85a 100644
--- a/aibridge/session.go
+++ b/aibridge/session.go
@@ -55,6 +55,12 @@ func GuessSessionID(client Client, r *http.Request) *string {
 		}
 		return cleanRef(matches[1])
 	case ClientCodex:
+		// Codex renamed the header from "session_id" to "session-id" in
+		// newer releases. Check the current name first, then fall back to
+		// the legacy name for older Codex versions.
+		if sid := cleanRef(r.Header.Get("session-id")); sid != nil {
+			return sid
+		}
 		return cleanRef(r.Header.Get("session_id"))
 	case ClientMux:
 		return cleanRef(r.Header.Get("X-Mux-Workspace-Id"))
diff --git a/aibridge/session_test.go b/aibridge/session_test.go
index 24d72d57a3..222f00a068 100644
--- a/aibridge/session_test.go
+++ b/aibridge/session_test.go
@@ -105,6 +105,18 @@ func TestGuessSessionID(t *testing.T) {
 			headers:   map[string]string{"session_id": "codex-session-123"},
 			sessionID: utils.PtrTo("codex-session-123"),
 		},
+		{
+			name:      "codex_with_hyphenated_session_header",
+			client:    aibridge.ClientCodex,
+			headers:   map[string]string{"session-id": "codex-session-456"},
+			sessionID: utils.PtrTo("codex-session-456"),
+		},
+		{
+			name:      "codex_hyphenated_header_takes_precedence",
+			client:    aibridge.ClientCodex,
+			headers:   map[string]string{"session-id": "codex-session-new", "session_id": "codex-session-old"},
+			sessionID: utils.PtrTo("codex-session-new"),
+		},
 		{
 			name:      "codex_with_whitespace_in_header",
 			client:    aibridge.ClientCodex,