diff --git a/README.md b/README.md
index d93ec0610c..bb78f03d3a 100644
--- a/README.md
+++ b/README.md
@@ -1492,6 +1492,8 @@ Python's standard-library HTTP client. Its fallback preserves spaces, Unicode, a
 reserved characters in search queries and label filters.
 File reads accept raw repository-relative paths and preserve spaces, Unicode,
 `#`, `?`, and literal percent signs with either HTTP client.
+Directory listings ask for the repository's own default branch, so a repository that
+uses neither `main` nor `master` reports its current tree instead of a stale branch.
 
 Users can explicitly activate an enabled skill for a single turn by starting the request with `/skill-name`, for example `/data-analysis analyze uploads/foo.csv`. DeerFlow loads that skill's `SKILL.md` as hidden current-turn context while leaving the base prompt limited to skill metadata. Slash activation respects disabled skills, custom-agent skill whitelists, and existing channel commands such as `/new` and `/help`.
 
diff --git a/skills/public/github-deep-research/scripts/github_api.py b/skills/public/github-deep-research/scripts/github_api.py
index 2e9b4dfdf9..dad88ec94a 100644
--- a/skills/public/github-deep-research/scripts/github_api.py
+++ b/skills/public/github-deep-research/scripts/github_api.py
@@ -101,17 +101,17 @@ class GitHubAPI:
             return f"[README not found: {e}]"
 
     def get_tree(
-        self, owner: str, repo: str, branch: str = "main", recursive: bool = True
+        self, owner: str, repo: str, branch: str = "HEAD", recursive: bool = True
     ) -> Dict:
-        """Get repository directory tree."""
+        """Get repository directory tree.
+
+        ``HEAD`` is resolved by GitHub to the repository's default branch, so a
+        repository that uses neither ``main`` nor ``master`` gets its current tree.
+        Guessing those two names instead served the tree of an abandoned branch
+        whenever the repository kept a stale ``master`` around.
+        """
         params = {"recursive": "1"} if recursive else {}
-        try:
-            return self._get(f"/repos/{owner}/{repo}/git/trees/{branch}", params)
-        except Exception:
-            # Try 'master' if 'main' fails
-            if branch == "main":
-                return self._get(f"/repos/{owner}/{repo}/git/trees/master", params)
-            raise
+        return self._get(f"/repos/{owner}/{repo}/git/trees/{branch}", params)
 
     def get_file_content(self, owner: str, repo: str, path: str) -> str:
         """Get content of a file using its raw repository-relative path."""
diff --git a/tests/skills/test_github_deep_research.py b/tests/skills/test_github_deep_research.py
index 2168e12443..d89683227c 100644
--- a/tests/skills/test_github_deep_research.py
+++ b/tests/skills/test_github_deep_research.py
@@ -130,3 +130,43 @@ def test_fallback_without_parameters(fallback_client):
     assert client.get_repo_info("owner", "repo") == {"ok": True}
 
     assert captured["url"] == "https://api.github.com/repos/owner/repo"
+
+
+def test_tree_asks_for_the_repository_head(file_content_client):
+    client, captured = file_content_client
+
+    assert client.get_tree("owner", "repo") == {"ok": True}
+
+    url = urlsplit(captured["url"])
+    assert url.path == "/repos/owner/repo/git/trees/HEAD"
+    assert parse_qs(url.query) == {"recursive": ["1"]}
+
+
+def test_tree_keeps_an_explicit_branch(file_content_client):
+    client, captured = file_content_client
+
+    assert client.get_tree("owner", "repo", branch="dev", recursive=False) == {
+        "ok": True
+    }
+
+    url = urlsplit(captured["url"])
+    assert url.path == "/repos/owner/repo/git/trees/dev"
+    assert url.query == ""
+
+
+def test_tree_does_not_guess_another_branch(monkeypatch, fallback_client):
+    client, _ = fallback_client
+    asked: list[str] = []
+
+    def fail_after_recording(endpoint, params=None, accept=None):
+        asked.append(endpoint)
+        raise RuntimeError("HTTP 404")
+
+    monkeypatch.setattr(client, "_get", fail_after_recording)
+
+    with pytest.raises(RuntimeError):
+        client.get_tree("owner", "repo")
+
+    # A stale `master` still resolves as a branch, so retrying names here silently
+    # returns the stale branch's tree instead of failing.
+    assert asked == ["/repos/owner/repo/git/trees/HEAD"]