diff --git a/crates/adapter/src/fastly/core.rs b/crates/adapter/src/fastly/core.rs
index cb1e1c34..da8f21e0 100644
--- a/crates/adapter/src/fastly/core.rs
+++ b/crates/adapter/src/fastly/core.rs
@@ -1854,6 +1854,11 @@ pub mod fastly_http_req {
 
         res
     }
+
+    #[export_name = "fastly_http_req#on_behalf_of"]
+    pub fn on_behalf_of(_: RequestHandle, _: *const u8, _: usize) -> FastlyStatus {
+        FastlyStatus::UNKNOWN_ERROR
+    }
 }
 
 pub mod fastly_http_resp {
diff --git a/lib/compute-at-edge-abi/cache.witx b/lib/compute-at-edge-abi/cache.witx
index 08930d92..fe9d4451 100644
--- a/lib/compute-at-edge-abi/cache.witx
+++ b/lib/compute-at-edge-abi/cache.witx
@@ -14,6 +14,8 @@
 (typename $cache_lookup_options
     (record
         (field $request_headers $request_handle) ;; a full request handle, but used only for its headers
+        (field $service_id (@witx pointer (@witx char8)))
+        (field $service_id_len u32)
     )
 )
 
@@ -21,6 +23,7 @@
     (flags (@witx repr u32)
         $reserved
         $request_headers
+        $service_id
     )
 )
 
@@ -29,6 +32,8 @@
     (record
         (field $request_headers $request_handle) ;; a full request handle, but used only for its headers
         (field $replace_strategy $cache_replace_strategy)
+        (field $service_id (@witx pointer (@witx char8)))
+        (field $service_id_len u32)
     )
 )
 
@@ -37,6 +42,7 @@
         $reserved
         $request_headers
         $replace_strategy
+        $service_id
     )
 )
 
@@ -65,6 +71,8 @@
         (field $user_metadata_ptr (@witx pointer u8))
         (field $user_metadata_len (@witx usize))
         (field $edge_max_age_ns $cache_duration_ns)
+        (field $service_id (@witx pointer (@witx char8)))
+        (field $service_id_len u32)
     )
 )
 
@@ -80,6 +88,7 @@
         $user_metadata
         $sensitive_data
         $edge_max_age_ns
+        $service_id
     )
 )
 
diff --git a/lib/compute-at-edge-abi/compute-at-edge.witx b/lib/compute-at-edge-abi/compute-at-edge.witx
index bb3e04e2..b2aba4f7 100644
--- a/lib/compute-at-edge-abi/compute-at-edge.witx
+++ b/lib/compute-at-edge-abi/compute-at-edge.witx
@@ -577,6 +577,14 @@
         (param $buf_len (@witx usize))
         (result $err (expected $num_bytes (error $fastly_status)))
     )
+
+    ;;; Instead of having this request cache in this service's space, use the
+    ;;; cache of the named service
+    (@interface func (export "on_behalf_of")
+        (param $req $request_handle)
+        (param $service string)
+        (result $err (expected (error $fastly_status)))
+    )
 )
 
 (module $fastly_http_resp
diff --git a/lib/src/component/http_req.rs b/lib/src/component/http_req.rs
index f67e3d2a..9a48e2bd 100644
--- a/lib/src/component/http_req.rs
+++ b/lib/src/component/http_req.rs
@@ -901,4 +901,12 @@ impl http_req::Host for ComponentCtx {
             too_large => Err(types::Error::BufferLen(too_large.unwrap_or(0))),
         }
     }
+
+    async fn on_behalf_of(
+        &mut self,
+        _: http_req::RequestHandle,
+        _: Vec<u8>,
+    ) -> Result<(), types::Error> {
+        Err(types::Error::Unsupported)
+    }
 }
diff --git a/lib/src/wiggle_abi/req_impl.rs b/lib/src/wiggle_abi/req_impl.rs
index 690d1967..5f71b873 100644
--- a/lib/src/wiggle_abi/req_impl.rs
+++ b/lib/src/wiggle_abi/req_impl.rs
@@ -1095,4 +1095,15 @@ impl FastlyHttpReq for Session {
             }),
         }
     }
+
+    fn on_behalf_of(
+        &mut self,
+        _memory: &mut GuestMemory<'_>,
+        _ds_req: RequestHandle,
+        _service: GuestPtr<str>,
+    ) -> Result<(), Error> {
+        Err(Error::Unsupported {
+            msg: "on_behalf_of is not supported in Viceroy",
+        })
+    }
 }
diff --git a/lib/wit/deps/fastly/compute.wit b/lib/wit/deps/fastly/compute.wit
index a336c344..43c57100 100644
--- a/lib/wit/deps/fastly/compute.wit
+++ b/lib/wit/deps/fastly/compute.wit
@@ -482,6 +482,11 @@ result<pending-request-handle, error>;
     info: inspect-config,
     max-len: u64
   ) -> result<string, error>;
+
+  on-behalf-of: func(
+    h: request-handle,
+    service: list<u8>,
+  ) -> result<_, error>;
 }
 
 /*