diff --git a/src/benchflow/agents/registry.py b/src/benchflow/agents/registry.py
index 0f00b33a..a00c3800 100644
--- a/src/benchflow/agents/registry.py
+++ b/src/benchflow/agents/registry.py
@@ -700,7 +700,7 @@ class AgentConfig:
         skill_paths=["$HOME/.opencode/skills"],
         home_dirs=[".opencode"],
         install_cmd=(
-            _js_agent_install("opencode", "opencode-ai")
+            _js_agent_install("opencode", "opencode-ai@1.17.20")
             + " && "
             + _opencode_family_proxy_wrapper_install(
                 "opencode", ".config/opencode/opencode.json"
diff --git a/tests/test_registry_invariants.py b/tests/test_registry_invariants.py
index 1227f91c..2671f3dc 100644
--- a/tests/test_registry_invariants.py
+++ b/tests/test_registry_invariants.py
@@ -259,6 +259,14 @@ def test_js_agent_install_respects_explicit_npm_package_specs():
     assert "some-agent@latest" in default_cmd
 
 
+def test_opencode_install_is_pinned_for_reproducible_harness_runs():
+    """Guards PR #931 against silently changing OpenCode between eval stages."""
+    install_cmd = AGENTS["opencode"].install_cmd
+
+    assert "opencode-ai@1.17.20" in install_cmd
+    assert "opencode-ai@latest" not in install_cmd
+
+
 def test_gemini_cli_install_is_pinned():
     """Guards v0.5-integration@27752fa against Daytona installing moving latest."""
     install_cmd = AGENTS["gemini"].install_cmd