diff --git a/pkg/authz/authorizers/cedar/core.go b/pkg/authz/authorizers/cedar/core.go
index e370653628..e66652a665 100644
--- a/pkg/authz/authorizers/cedar/core.go
+++ b/pkg/authz/authorizers/cedar/core.go
@@ -616,10 +616,20 @@ func (a *Authorizer) resolveClaims(identity *auth.Identity) (jwt.MapClaims, erro
 	// Embedded auth server path: the upstream IDP token is the primary claim source.
 	upstreamToken, tokenFound := identity.UpstreamTokens[a.primaryUpstreamProvider]
 	if !tokenFound || upstreamToken == "" {
-		// The upstream token must be present if the authorizer is configured to use it.
-		// Missing token means the session has no upstream credential; deny.
-		return nil, fmt.Errorf("upstream token for provider %q not found in identity",
-			a.primaryUpstreamProvider)
+		// RFC 8693 delegated tokens (and any token without an upstream session)
+		// have no UpstreamTokens entry — that binding only exists for an
+		// identity established via the upstream browser flow. Falling back to
+		// the request token's claims keeps delegation usable when Cedar is
+		// configured with a primaryUpstreamProvider (auto-derived from the
+		// sole upstream), rather than denying every tool before policy
+		// evaluation. This mirrors the existing opaque-token fallback branch
+		// below. See #6424.
+		a.claimKeyLog.Do(func() {
+			slog.Warn("upstream token not found for provider; falling back to request-token claims for Cedar evaluation",
+				"provider", a.primaryUpstreamProvider)
+		})
+		a.logClaimKeys("delegated-fallback", requestClaims)
+		return requestClaims, nil
 	}
 
 	upstreamClaims, err := parseUpstreamJWTClaims(upstreamToken)
diff --git a/pkg/authz/authorizers/cedar/core_test.go b/pkg/authz/authorizers/cedar/core_test.go
index bca48b8788..13e7a25d29 100644
--- a/pkg/authz/authorizers/cedar/core_test.go
+++ b/pkg/authz/authorizers/cedar/core_test.go
@@ -1404,8 +1404,12 @@ func TestAuthorizeWithJWTClaims_UpstreamProvider(t *testing.T) {
 				},
 				UpstreamTokens: map[string]string{},
 			},
-			wantErr:     true,
-			errContains: "upstream token for provider",
+			// Delegated tokens (RFC 8693) have no UpstreamTokens entry; the
+			// authorizer now falls back to request-token claims instead of
+			// erroring. Here the fallback sub does not match the policy, so
+			// authorization is denied by policy evaluation, not by a missing-
+			// token error. See #6424.
+			wantAuthorize: false,
 		},
 		{
 			name: "upstream_token_opaque_falls_back_to_request_claims_denied",
@@ -1469,8 +1473,29 @@ func TestAuthorizeWithJWTClaims_UpstreamProvider(t *testing.T) {
 				},
 				UpstreamTokens: nil,
 			},
-			wantErr:     true,
-			errContains: "upstream token for provider",
+			// Same fallback as above: a nil UpstreamTokens map (no tsid, as in
+			// a delegated token minted without an IDP session link) falls back
+			// to request claims rather than erroring. Policy evaluation then
+			// denies because sub mismatch.
+			wantAuthorize: false,
+		},
+		{
+			name: "delegated_token_missing_upstream_falls_back_and_permits_via_request_claims",
+			identity: &auth.Identity{
+				PrincipalInfo: auth.PrincipalInfo{
+					Subject: "upstream-user",
+					Claims: map[string]any{
+						"sub": "upstream-user",
+						"act": map[string]interface{}{"sub": "spiffe://toolhive.dev/ns/agents/sa/delegate"},
+					},
+				},
+				UpstreamTokens: nil,
+			},
+			// RFC 8693 delegated token has no upstream session (no tsid) and
+			// thus no UpstreamTokens entry. The fallback to request claims
+			// carries the delegated subject through, so a policy targeting the
+			// user still permits. See #6424.
+			wantAuthorize: true,
 		},
 		{
 			name: "upstream_token_has_no_sub_claim",