diff --git a/opam-ci-check/lib/lint.ml b/opam-ci-check/lib/lint.ml
index ecf01c3..6759bf1 100644
--- a/opam-ci-check/lib/lint.ml
+++ b/opam-ci-check/lib/lint.ml
@@ -378,9 +378,13 @@ module Checks = struct
       | List {pelem = (_::_ as reasons); _} when List.for_all is_valid_reason reasons -> []
       | _ -> [(pkg, InvalidReasonForArchiving)]
 
-
-  let x_opam_repository_commit_hash_at_time_of_archival ~pkg:_ _opam  =
-    [] (* TODO *)
+  let x_opam_repository_commit_hash_at_time_of_archival ~pkg  opam  =
+    opam
+    |> OpamFile.OPAM.extensions
+    |> OpamStd.String.Map.find_opt x_opam_repository_commit_hash_at_time_of_archiving_field
+    |> function
+    | Some {pelem = String _; _} -> []
+    | _ -> [(pkg, InvalidOpamRepositoryCommitHash)]
 
   let checks kinds ~newly_published ~opam_repo_dir ~pkg_src_dir repo_package_names =
     let general_opam_file_checks () =
diff --git a/opam-ci-check/lib/lint_error.ml b/opam-ci-check/lib/lint_error.ml
index da05616..3fb67f6 100644
--- a/opam-ci-check/lib/lint_error.ml
+++ b/opam-ci-check/lib/lint_error.ml
@@ -38,13 +38,16 @@ type error =
   | DefaultTagsPresent of string list
   | MissingUpperBound of string
   | InvalidReasonForArchiving
+  | InvalidOpamRepositoryCommitHash
 
 (**/**)
 
+(* These x_ fields are used in the opam repo archive *)
 let x_reason_for_archiving_field = "x-reason-for-archiving"
-(* Used in the opam repo archive *)
 let x_reason_for_archiving_valid_reasons =
   ["ocaml-version"; "source-unavailable"; "maintenance-intent"; "uninstallable" ]
+let x_opam_repository_commit_hash_at_time_of_archiving_field =
+  "x-opam-repository-commit-hash-at-time-of-archiving"
 
 let msg_of_prefix_conflict_class_mismatch ~pkg = function
   | WrongPrefix { conflict_class; required_prefix } ->
@@ -180,3 +183,9 @@ let msg_of_error (package, (err : error)) =
          of one or more of the valid reasons %s"
         pkg x_reason_for_archiving_field
         (String.concat ", " x_reason_for_archiving_valid_reasons)
+  | InvalidOpamRepositoryCommitHash ->
+      Printf.sprintf
+        "Error in %s: The field '%s' must be present and hold a string \
+         recording the commit hash of the primary repo at the time the package \
+         version is archived."
+        pkg x_opam_repository_commit_hash_at_time_of_archiving_field
diff --git a/opam-ci-check/test/lint.t b/opam-ci-check/test/lint.t
index f5a9f07..2a7ae8f 100644
--- a/opam-ci-check/test/lint.t
+++ b/opam-ci-check/test/lint.t
@@ -363,7 +363,10 @@ https://github.com/ocaml/opam-repository/blob/master/governance/policies/archivi
 
 Test that we do not report an error on a minimal well-formed package:
 
-  $ echo 'x-reason-for-archiving: [ "source-unavailable" ]' >> packages/a-1/a-1.0.0.1/opam
+  $ echo 'x-reason-for-archiving: [ "source-unavailable" ]' \
+  > >> packages/a-1/a-1.0.0.1/opam
+  $ echo 'x-opam-repository-commit-hash-at-time-of-archiving: "de786e28dbea73843ad5e5f0290a4e81fba39370"' \
+  > >> packages/a-1/a-1.0.0.1/opam
   $ cat packages/a-1/a-1.0.0.1/opam
   opam-version: "2.0"
   synopsis: "Synopsis"
@@ -378,6 +381,7 @@ Test that we do not report an error on a minimal well-formed package:
   build: []
   depends: []
   x-reason-for-archiving: [ "source-unavailable" ]
+  x-opam-repository-commit-hash-at-time-of-archiving: "de786e28dbea73843ad5e5f0290a4e81fba39370"
   $ opam-ci-check lint -r . --check=archive-repo a-1.0.0.1
   Linting opam-repository at $TESTCASE_ROOT/. ...
   No errors
@@ -461,3 +465,37 @@ Test we report an error when the x-reason-for-archiving has an invalid reason:
   Linting opam-repository at $TESTCASE_ROOT/. ...
   Error in a-1.0.0.1: The field 'x-reason-for-archiving' must be present and hold a nonempty list of one or more of the valid reasons ocaml-version, source-unavailable, maintenance-intent, uninstallable
   [1]
+
+Test we do NOT report an error when the x-reason-for-archiving has multiple invalid reasons:
+
+  $ sed \
+  > -e 's/x-reason-for-archiving:.*/x-reason-for-archiving: ["source-unavailable" "maintenance-intent"]/' \
+  > packages/a-1/a-1.0.0.1/opam > opam.new
+  $ mv opam.new packages/a-1/a-1.0.0.1/opam
+  $ opam-ci-check lint -r . --check=archive-repo a-1.0.0.1
+  Linting opam-repository at $TESTCASE_ROOT/. ...
+  No errors
+
+# x-opam-repository-commit-hash-at-time-of-archiving checks
+
+Test we report an error when the x-opam-repository-commit-hash-at-time-of-archiving
+is missing:
+
+  $ sed \
+  > -e '/x-opam-repository-commit-hash-at-time-of-archiving/d' \
+  > packages/a-1/a-1.0.0.1/opam > opam.new
+  $ mv opam.new packages/a-1/a-1.0.0.1/opam
+  $ opam-ci-check lint -r . --check=archive-repo a-1.0.0.1
+  Linting opam-repository at $TESTCASE_ROOT/. ...
+  Error in a-1.0.0.1: The field 'x-opam-repository-commit-hash-at-time-of-archiving' must be present and hold a string recording the commit hash of the primary repo at the time the package version is archived.
+  [1]
+
+Test we report an error when the x-opam-repository-commit-hash-at-time-of-archiving
+has an invald value:
+
+  $ echo 'x-opam-repository-commit-hash-at-time-of-archiving: false' \
+  > >> packages/a-1/a-1.0.0.1/opam
+  $ opam-ci-check lint -r . --check=archive-repo a-1.0.0.1
+  Linting opam-repository at $TESTCASE_ROOT/. ...
+  Error in a-1.0.0.1: The field 'x-opam-repository-commit-hash-at-time-of-archiving' must be present and hold a string recording the commit hash of the primary repo at the time the package version is archived.
+  [1]