diff --git a/test-tools/ossl_test_tools/crltest/__init__.py b/test-tools/ossl_test_tools/crltest/__init__.py
index b6c27011..1aeec30c 100644
--- a/test-tools/ossl_test_tools/crltest/__init__.py
+++ b/test-tools/ossl_test_tools/crltest/__init__.py
@@ -14,13 +14,14 @@
 
 from pathlib import Path
 
-from . import alt_ta, indirect, no_chain
+from . import alt_ta, delta, indirect, no_chain
 
 
 def _all_cmd(args):
     indirect.build(args.source)
     alt_ta.build(args.source)
     no_chain.build(args.source)
+    delta.build(args.source)
     print(f"regenerated all indirect-CRL artifacts in {args.source}")
 
 
@@ -34,7 +35,8 @@ def register(subparsers):
     indirect.register(sub)
     alt_ta.register(sub)
     no_chain.register(sub)
+    delta.register(sub)
 
-    p = sub.add_parser("all", help="Run indirect, alt-ta, and no-chain in order.")
+    p = sub.add_parser("all", help="Run indirect, alt-ta, no-chain, and delta in order.")
     p.add_argument("--source", type=Path, required=True, help="Path to crltest.c")
     p.set_defaults(func=_all_cmd)
diff --git a/test-tools/ossl_test_tools/crltest/delta.py b/test-tools/ossl_test_tools/crltest/delta.py
new file mode 100644
index 00000000..0ac36cd7
--- /dev/null
+++ b/test-tools/ossl_test_tools/crltest/delta.py
@@ -0,0 +1,103 @@
+# Copyright 2026 The OpenSSL Project Authors. All Rights Reserved.
+#
+# Licensed under the Apache License 2.0 (the "License").  You may not use
+# this file except in compliance with the License.  You can obtain a copy
+# in the file LICENSE in the source distribution or at
+# https://www.openssl.org/source/license.html
+
+"""Delta-CRL artifacts for the X509_V_FLAG_USE_DELTAS path.
+
+  kCrlDeltaBase    full CRL signed by kRoot, no revocations, carries a
+                   Freshest CRL extension so EXFLAG_FRESHEST is set and
+                   get_delta_sk() looks for a delta
+  kCrlDeltaValid   delta CRL (deltaCRLIndicator -> base crlNumber) that
+                   revokes kLeaf, valid time window around kVerify
+
+Both CRLs are issued and signed by kRoot and share an identical
+AuthorityKeyIdentifier (and no IDP), so check_delta_base() pairs the delta
+with the base.  kRoot, kRootPrivateKey and kLeaf are read out of the source
+file by name; no new certificates are generated.
+
+The time window matches the indirect suite (CRL_LAST_UPDATE/CRL_NEXT_UPDATE)
+so kVerify falls inside it: this exercises the happy path where the delta is
+current.  The expired-delta regression case is intentionally not generated
+here.
+"""
+
+import datetime
+from pathlib import Path
+
+from cryptography import x509
+from cryptography.hazmat.primitives import hashes
+
+from .. import cert_util
+from ._shared import CRL_LAST_UPDATE, CRL_NEXT_UPDATE, UTC
+
+BASE_CRL_NUMBER = 0x1000
+DELTA_CRL_NUMBER = 0x1001
+REVOCATION_DATE = datetime.datetime(2026, 3, 20, 0, 0, 0, tzinfo=UTC)
+
+
+def build(source_path):
+    root_cert = cert_util.cert_from_c(source_path, "kRoot")
+    root_key = cert_util.key_from_c(source_path, "kRootPrivateKey")
+    leaf_cert = cert_util.cert_from_c(source_path, "kLeaf")
+    akid = cert_util.akid_from_cert(root_cert)
+
+    base_crl = (
+        x509.CertificateRevocationListBuilder()
+        .issuer_name(root_cert.subject)
+        .last_update(CRL_LAST_UPDATE)
+        .next_update(CRL_NEXT_UPDATE)
+        .add_extension(akid, critical=False)
+        .add_extension(x509.CRLNumber(BASE_CRL_NUMBER), critical=False)
+        .add_extension(
+            x509.FreshestCRL([
+                x509.DistributionPoint(
+                    full_name=[x509.UniformResourceIdentifier(
+                        "http://crl.example.com/delta.crl"
+                    )],
+                    relative_name=None,
+                    reasons=None,
+                    crl_issuer=None,
+                ),
+            ]),
+            critical=False)
+        .sign(private_key=root_key, algorithm=hashes.SHA256())
+    )
+
+    revoked = (
+        x509.RevokedCertificateBuilder()
+        .serial_number(leaf_cert.serial_number)
+        .revocation_date(REVOCATION_DATE)
+        .build()
+    )
+    delta_crl = (
+        x509.CertificateRevocationListBuilder()
+        .issuer_name(root_cert.subject)
+        .last_update(CRL_LAST_UPDATE)
+        .next_update(CRL_NEXT_UPDATE)
+        .add_revoked_certificate(revoked)
+        .add_extension(akid, critical=False)
+        .add_extension(x509.CRLNumber(DELTA_CRL_NUMBER), critical=False)
+        .add_extension(x509.DeltaCRLIndicator(BASE_CRL_NUMBER), critical=True)
+        .sign(private_key=root_key, algorithm=hashes.SHA256())
+    )
+
+    cert_util.update_crl_in_c(source_path, "kCrlDeltaBase", base_crl)
+    cert_util.update_crl_in_c(source_path, "kCrlDeltaValid", delta_crl)
+
+
+def _cmd(args):
+    build(args.source)
+    print(f"updated kCrlDeltaBase kCrlDeltaValid in {args.source}")
+
+
+def register(sub):
+    p = sub.add_parser(
+        "delta",
+        help="Regenerate the delta-CRL artifacts (base + valid delta) for the "
+             "USE_DELTAS path.",
+    )
+    p.add_argument("--source", type=Path, required=True, help="Path to crltest.c")
+    p.set_defaults(func=_cmd)