diff --git a/swh/loader/package/archive/loader.py b/swh/loader/package/archive/loader.py
--- a/swh/loader/package/archive/loader.py
+++ b/swh/loader/package/archive/loader.py
@@ -24,25 +24,40 @@
 @attr.s
 class ArchivePackageInfo(BasePackageInfo):
     raw_info = attr.ib(type=Dict[str, Any])
-    length = attr.ib(type=int)
-    """Size of the archive file"""
-    time = attr.ib(type=Union[str, datetime.datetime])
-    """Timestamp of the archive file on the server"""
+
+    length = attr.ib(type=Optional[int], default=None)
+    """Optional size of the archive file if integrity is provided."""
+    time = attr.ib(type=Optional[Union[str, datetime.datetime]], default=None)
+    """Optional timestamp of the archive file on the server if integrity is provided."""
+    version = attr.ib(type=Optional[str], default=None)  # type: ignore
+    """(Override) Optional version if integrity is provided."""
+    integrity = attr.ib(type=Optional[str], default=None)
+    """Archive integrity field"""
 
     # default format for gnu
     MANIFEST_FORMAT = string.Template("$time $length $version $url")
+    # default format for nixguix manifests (e.g. nixpkgs, guix)
+    INTEGRITY_MANIFEST_FORMAT = string.Template("$integrity $url")
+    INTEGRITY_EXTID_TYPE = "package-manifest-integrity"
 
     def extid(self, manifest_format: Optional[string.Template] = None) -> PartialExtID:
         """Returns a unique intrinsic identifier of this package info
 
         ``manifest_format`` allows overriding the class' default MANIFEST_FORMAT"""
-        manifest_format = manifest_format or self.MANIFEST_FORMAT
+
+        if self.raw_info.get("integrity") is not None:
+            manifest_format = manifest_format or self.INTEGRITY_MANIFEST_FORMAT
+            extid_type = self.INTEGRITY_EXTID_TYPE
+        else:
+            manifest_format = manifest_format or self.MANIFEST_FORMAT
+            extid_type = self.EXTID_TYPE
+
         # TODO: use parsed attributes instead of self.raw_info
         manifest = manifest_format.substitute(
             {k: str(v) for (k, v) in self.raw_info.items()}
         )
         return (
-            self.EXTID_TYPE,
+            extid_type,
             self.EXTID_VERSION,
             hashlib.sha256(manifest.encode()).digest(),
         )
@@ -50,15 +65,30 @@
     @classmethod
     def from_metadata(cls, a_metadata: Dict[str, Any]) -> "ArchivePackageInfo":
         url = a_metadata["url"]
-        filename = a_metadata.get("filename")
-        return cls(
-            url=url,
-            filename=filename if filename else path.split(url)[-1],
-            raw_info=a_metadata,
-            length=a_metadata["length"],
-            time=a_metadata["time"],
-            version=a_metadata["version"],
-        )
+        integrity = a_metadata.get("integrity")
+        filename_ = a_metadata.get("filename")
+        filename = filename_ if filename_ else path.split(url)[-1]
+        if integrity is not None:
+            return cls(
+                url=url,
+                filename=filename,
+                raw_info=a_metadata,
+                integrity=integrity,
+            )
+        else:
+            length = a_metadata["length"]
+            time = a_metadata["time"]
+            version = a_metadata["version"]
+            assert length is not None
+            assert version is not None
+            return cls(
+                url=url,
+                filename=filename,
+                raw_info=a_metadata,
+                length=length,
+                time=time,
+                version=version,
+            )
 
 
 class ArchiveLoader(PackageLoader[ArchivePackageInfo]):
@@ -141,6 +171,7 @@
         self, p_info: ArchivePackageInfo, uncompressed_path: str, directory: Sha1Git
     ) -> Optional[Release]:
         time = p_info.time  # assume it's a timestamp
+        parsed_time: Optional[datetime.datetime]
         if isinstance(time, str):  # otherwise, assume it's a parsable date
             parsed_time = iso8601.parse_date(time)
         else:
@@ -151,8 +182,15 @@
             else None
         )
         msg = f"Synthetic release for archive at {p_info.url}\n"
+        if p_info.version is not None:
+            name = p_info.version.encode()
+        elif p_info.integrity is not None:
+            name = p_info.integrity.encode()
+        else:
+            raise ValueError("Either version or integrity must be provided.")
+
         return Release(
-            name=p_info.version.encode(),
+            name=name,
             message=msg.encode(),
             date=normalized_time,
             author=EMPTY_AUTHOR,
diff --git a/swh/loader/package/archive/tests/test_archive.py b/swh/loader/package/archive/tests/test_archive.py
--- a/swh/loader/package/archive/tests/test_archive.py
+++ b/swh/loader/package/archive/tests/test_archive.py
@@ -9,6 +9,7 @@
 from io import BytesIO
 from pathlib import Path
 import string
+from typing import Optional
 
 import attr
 import pytest
@@ -339,8 +340,9 @@
 
     @attr.s
     class TestPackageInfo(ArchivePackageInfo):
-        a = attr.ib()
-        b = attr.ib()
+        # mandatory change since ArchivePackageinfo defines optional values
+        a = attr.ib(type=Optional[str], default=None)
+        b = attr.ib(type=Optional[str], default=None)
 
     metadata = GNU_ARTIFACTS[0]