diff --git a/backend/app/services/c2/mythic.py b/backend/app/services/c2/mythic.py
index c430afa..cb83221 100644
--- a/backend/app/services/c2/mythic.py
+++ b/backend/app/services/c2/mythic.py
@@ -1,7 +1,8 @@
 # Contract pinned from MythicMeta/Mythic_Scripting master @ 2026-06-10 (raw.githubusercontent.com/MythicMeta/Mythic_Scripting/master/mythic/mythic.py)
+# Sprint 10 correction: /graphql/ MUST have trailing slash (matches mythic_utilities.get_http_transport).
 """Mythic 3.x C2 adapter.
 
-Transport: POST https://<host>:7443/graphql
+Transport: POST https://<host>:7443/graphql/
 Header: apitoken: <token>
 Backend: Hasura-proxied Postgres behind nginx.
 
@@ -116,7 +117,7 @@ class MythicAdapter(C2Adapter):
     """Real Mythic 3.x adapter using GraphQL over HTTP."""
 
     def __init__(self, url: str, api_token: str, verify_tls: bool = False) -> None:
-        self._url = url.rstrip("/") + "/graphql"
+        self._url = url.rstrip("/") + "/graphql/"
         self._token = api_token
         self._verify = verify_tls
         if not verify_tls:
diff --git a/backend/tests/test_c2_adapter_mythic.py b/backend/tests/test_c2_adapter_mythic.py
index de32055..3ec77c2 100644
--- a/backend/tests/test_c2_adapter_mythic.py
+++ b/backend/tests/test_c2_adapter_mythic.py
@@ -9,7 +9,7 @@ from backend.app.services.c2.adapter import C2Error
 from backend.app.services.c2.mythic import MythicAdapter
 
 _BASE_URL = "https://mythic.lab:7443"
-_GQL_URL = _BASE_URL + "/graphql"
+_GQL_URL = _BASE_URL + "/graphql/"
 _TOKEN = "fake-api-token"
 
 
@@ -143,9 +143,19 @@ class TestMythicAdapterNoRedirects:
         """Adapter must not follow HTTP redirects (allow_redirects=False)."""
         with rm_module.Mocker() as m:
             # Simulate a redirect response; requests-mock won't auto-follow it.
-            m.post(_GQL_URL, status_code=301, headers={"Location": "https://evil.example/graphql"})
+            m.post(_GQL_URL, status_code=301, headers={"Location": "https://evil.example/graphql/"})
             # With allow_redirects=False the 301 is treated as a non-2xx → raise_for_status raises.
             with pytest.raises(C2Error):
                 adapter.list_callbacks()
             # Exactly one request was made — no follow-up to Location.
             assert len(m.request_history) == 1
+
+
+class TestMythicAdapterUrlConstruction:
+    def test_mythic_adapter_url_has_trailing_slash(self):
+        a1 = MythicAdapter(url="https://x:7443", api_token="t")
+        assert a1._url == "https://x:7443/graphql/"
+        a2 = MythicAdapter(url="https://x:7443/", api_token="t")
+        assert a2._url == "https://x:7443/graphql/"
+        a3 = MythicAdapter(url="https://x:7443///", api_token="t")
+        assert a3._url == "https://x:7443/graphql/"
diff --git a/backend/tests/test_c2_adapter_mythic_m3.py b/backend/tests/test_c2_adapter_mythic_m3.py
index e6d5963..a749616 100644
--- a/backend/tests/test_c2_adapter_mythic_m3.py
+++ b/backend/tests/test_c2_adapter_mythic_m3.py
@@ -9,7 +9,7 @@ from backend.app.services.c2.adapter import C2Error
 from backend.app.services.c2.mythic import MythicAdapter
 
 _BASE_URL = "https://mythic.lab:7443"
-_GQL_URL = _BASE_URL + "/graphql"
+_GQL_URL = _BASE_URL + "/graphql/"
 _TOKEN = "fake-api-token"
 
 
diff --git a/backend/tests/test_c2_adapter_mythic_m4.py b/backend/tests/test_c2_adapter_mythic_m4.py
index 5103185..206eb76 100644
--- a/backend/tests/test_c2_adapter_mythic_m4.py
+++ b/backend/tests/test_c2_adapter_mythic_m4.py
@@ -9,7 +9,7 @@ from backend.app.services.c2.adapter import C2Error, C2HistoricalTask
 from backend.app.services.c2.mythic import MythicAdapter
 
 _BASE_URL = "https://mythic.lab:7443"
-_GQL_URL = _BASE_URL + "/graphql"
+_GQL_URL = _BASE_URL + "/graphql/"
 _TOKEN = "fake-api-token"