diff --git a/src/agent_env/agents/agents/claude-code/claude_bridge.py b/src/agent_env/agents/agents/claude-code/claude_bridge.py
index fad10df25..e8fcfc651 100644
--- a/src/agent_env/agents/agents/claude-code/claude_bridge.py
+++ b/src/agent_env/agents/agents/claude-code/claude_bridge.py
@@ -189,6 +189,10 @@ def cli_env(environ: Mapping[str, str], *, model: str | None = None, project_id:
     if model and env.get("ANTHROPIC_BASE_URL"):
         for alias in _MODEL_ALIASES:
             env.setdefault(alias, model)
+        if "claude" not in model.lower():
+            # The CLI sends Anthropic's beta parameters, such as `context_management`, whatever the model; an endpoint
+            # serving another provider's model through the Messages API, as LiteLLM does, refuses them with a 400.
+            env.setdefault("CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS", "1")
     headers = _with_attribution(_model_headers(env.get(MODEL_HEADERS_ENV)), _attribution_headers(project_id, task_id))
     if headers:
         env["ANTHROPIC_CUSTOM_HEADERS"] = "\n".join(f"{name}: {value}" for name, value in headers.items())
diff --git a/tst/unit/agents/claude_code/test_cli_env.py b/tst/unit/agents/claude_code/test_cli_env.py
index 7c92fcc82..c76b7d48d 100644
--- a/tst/unit/agents/claude_code/test_cli_env.py
+++ b/tst/unit/agents/claude_code/test_cli_env.py
@@ -46,6 +46,22 @@ def test_the_cli_offers_its_tools_up_front_unless_tool_search_is_asked_for():
     assert claude_bridge.cli_env({**GATEWAY, "ENABLE_TOOL_SEARCH": "auto"})["ENABLE_TOOL_SEARCH"] == "auto"
 
 
+@pytest.mark.parametrize("model, disabled", [
+    ("fireworks_ai/glm-5p3-flash", "1"),
+    ("claude-sonnet-5-5", None),
+    ("bedrock/us.anthropic.claude-opus-5-5", None),
+])
+def test_a_model_that_isnt_claude_is_sent_none_of_anthropics_beta_parameters(model, disabled):
+    """LiteLLM refuses `context_management`, which the CLI sends for any model, when the model isn't Anthropic's."""
+    assert claude_bridge.cli_env(GATEWAY, model=model).get("CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS") == disabled
+
+
+def test_an_explicit_beta_setting_wins():
+    env = claude_bridge.cli_env({**GATEWAY, "CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS": "0"}, model="fireworks_ai/x")
+
+    assert env["CLAUDE_CODE_DISABLE_EXPERIMENTAL_BETAS"] == "0"
+
+
 def test_no_endpoint_leaves_the_cli_to_its_own_and_an_api_key_alone():
     env = claude_bridge.cli_env({"ANTHROPIC_API_KEY": "direct"}, model="claude-x")