diff --git a/src/pip/_internal/index/package_finder.py b/src/pip/_internal/index/package_finder.py
index db416b499..578c0b19c 100644
--- a/src/pip/_internal/index/package_finder.py
+++ b/src/pip/_internal/index/package_finder.py
@@ -2,6 +2,7 @@
 
 import enum
 import functools
+import gzip
 import itertools
 import json
 import logging
@@ -935,7 +936,7 @@ class PackageFinder:
     def _try_load_parsed_links_cache(parsed_links_path: Path) -> Optional[List[Link]]:
         page_links: Optional[List[Link]] = None
         try:
-            with parsed_links_path.open("r") as f:
+            with gzip.open(parsed_links_path, mode="rt", encoding="utf-8") as f:
                 logger.debug("reading page links from cache %s", parsed_links_path)
                 cached_links = json.load(f)
                 page_links = []
@@ -967,7 +968,7 @@ class PackageFinder:
             page_links.append(link)
 
         logger.debug("writing page links to %s", parsed_links_path)
-        with parsed_links_path.open("w") as f:
+        with gzip.open(parsed_links_path, mode="wt", encoding="utf-8") as f:
             json.dump(cacheable_links, f)
 
         return page_links
@@ -977,7 +978,7 @@ class PackageFinder:
         cached_candidates_path: Path,
     ) -> Optional[List[InstallationCandidate]]:
         try:
-            with cached_candidates_path.open("r") as f:
+            with gzip.open(cached_candidates_path, mode="rt", encoding="utf-8") as f:
                 serialized_candidates = json.load(f)
             logger.debug("read serialized candidates from %s", cached_candidates_path)
             package_links: List[InstallationCandidate] = []
@@ -1011,7 +1012,7 @@ class PackageFinder:
             )
             for candidate in candidates
         ]
-        with cached_candidates_path.open("w") as f:
+        with gzip.open(cached_candidates_path, mode="wt", encoding="utf-8") as f:
             logger.debug("writing serialized candidates to %s", f.name)
             json.dump(serialized_candidates, f)
         return candidates