diff --git a/src/adcp/__main__.py b/src/adcp/__main__.py
index e45e7d6e2..09aa87948 100644
--- a/src/adcp/__main__.py
+++ b/src/adcp/__main__.py
@@ -397,6 +397,41 @@ async def _dispatch_tool(client: ADCPClient, tool_name: str, payload: dict[str,
         )
 
 
+_HEADER_FORBIDDEN = ("\r", "\n", "\x00")
+
+
+def parse_header_args(header_args: list[str] | None) -> dict[str, str] | None:
+    """Parse repeated --header KEY=VALUE arguments into a dict."""
+    if not header_args:
+        return None
+    result: dict[str, str] = {}
+    for raw in header_args:
+        key, sep, value = raw.partition("=")
+        if not sep:
+            print(
+                f"Error: --header value must be KEY=VALUE, got: {raw!r}",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+        if not key:
+            print(f"Error: --header key cannot be empty in: {raw!r}", file=sys.stderr)
+            sys.exit(1)
+        if any(c in key for c in _HEADER_FORBIDDEN):
+            print(
+                f"Error: --header key contains illegal characters (CRLF/null): {key!r}",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+        if any(c in value for c in _HEADER_FORBIDDEN):
+            print(
+                f"Error: --header value for {key!r} contains illegal characters (CRLF/null)",
+                file=sys.stderr,
+            )
+            sys.exit(1)
+        result[key] = value
+    return result or None
+
+
 def load_payload(payload_arg: str | None) -> dict[str, Any]:
     """Load payload from argument (JSON, @file, or stdin)."""
     if not payload_arg:
@@ -424,7 +459,12 @@ def load_payload(payload_arg: str | None) -> dict[str, Any]:
         sys.exit(1)
 
 
-def handle_save_auth(alias: str, url: str | None, protocol: str | None) -> None:
+def handle_save_auth(
+    alias: str,
+    url: str | None,
+    protocol: str | None,
+    extra_headers: dict[str, str] | None = None,
+) -> None:
     """Handle --save-auth command."""
     if not url:
         # Interactive mode
@@ -438,7 +478,7 @@ def handle_save_auth(alias: str, url: str | None, protocol: str | None) -> None:
 
     auth_token = input("Auth token (optional): ").strip() or None
 
-    save_agent(alias, url, protocol, auth_token)
+    save_agent(alias, url, protocol, auth_token, extra_headers or None)
     print(f"✓ Saved agent '{alias}'")
 
 
@@ -457,6 +497,9 @@ def handle_list_agents() -> None:
         print(f"    URL: {config.get('agent_uri')}")
         print(f"    Protocol: {config.get('protocol', 'mcp').upper()}")
         print(f"    Auth: {auth}")
+        extra_h = config.get("extra_headers")
+        if extra_h:
+            print(f"    Extra headers: {', '.join(extra_h.keys())}")
 
 
 def handle_remove_agent(alias: str) -> None:
@@ -520,6 +563,14 @@ def main() -> None:
     # Execution options
     parser.add_argument("--protocol", choices=["mcp", "a2a"], help="Force protocol type")
     parser.add_argument("--auth", help="Authentication token")
+    parser.add_argument(
+        "--header",
+        "-H",
+        metavar="KEY=VALUE",
+        action="append",
+        dest="headers",
+        help="Extra request header (repeatable, e.g. --header x-adcp-tenant=acme)",
+    )
     parser.add_argument("--json", action="store_true", help="Output as JSON")
     parser.add_argument("--debug", action="store_true", help="Enable debug mode")
     parser.add_argument("--help", "-h", action="store_true", help="Show help")
@@ -572,7 +623,8 @@ def main() -> None:
     if args.save_auth:
         url = args.agent if args.agent else None
         protocol = args.tool if args.tool else None
-        handle_save_auth(args.save_auth, url, protocol)
+        parsed_extra_headers = parse_header_args(args.headers)
+        handle_save_auth(args.save_auth, url, protocol, parsed_extra_headers)
         sys.exit(0)
 
     if args.list_agents:
@@ -609,6 +661,12 @@ def main() -> None:
     if args.debug:
         agent_config["debug"] = True
 
+    extra_headers = parse_header_args(args.headers)
+    if extra_headers:
+        # Merge CLI headers on top of any stored per-agent extra_headers
+        stored: dict[str, str] = agent_config.get("extra_headers") or {}
+        agent_config["extra_headers"] = {**stored, **extra_headers}
+
     # Load payload
     payload = load_payload(args.payload)
 
diff --git a/src/adcp/config.py b/src/adcp/config.py
index 95d09127d..595fb19d9 100644
--- a/src/adcp/config.py
+++ b/src/adcp/config.py
@@ -38,7 +38,11 @@ def save_config(config: dict[str, Any]) -> None:
 
 
 def save_agent(
-    alias: str, url: str, protocol: str | None = None, auth_token: str | None = None
+    alias: str,
+    url: str,
+    protocol: str | None = None,
+    auth_token: str | None = None,
+    extra_headers: dict[str, str] | None = None,
 ) -> None:
     """Save agent configuration."""
     config = load_config()
@@ -54,6 +58,9 @@ def save_agent(
     if auth_token:
         config["agents"][alias]["auth_token"] = auth_token
 
+    if extra_headers:
+        config["agents"][alias]["extra_headers"] = extra_headers
+
     save_config(config)
 
 
diff --git a/src/adcp/protocols/a2a.py b/src/adcp/protocols/a2a.py
index 1d9a2a996..bd9615d55 100644
--- a/src/adcp/protocols/a2a.py
+++ b/src/adcp/protocols/a2a.py
@@ -227,12 +227,24 @@ async def _get_httpx_client(self) -> httpx.AsyncClient:
                 keepalive_expiry=30.0,
             )
 
-            headers = {}
+            headers: dict[str, str] = {}
+            if self.agent_config.extra_headers:
+                headers.update(self.agent_config.extra_headers)
             if self.agent_config.auth_token:
+                # auth always wins on conflict
                 if self.agent_config.auth_type == "bearer":
-                    headers["Authorization"] = f"Bearer {self.agent_config.auth_token}"
+                    auth_header_name = "Authorization"
+                    auth_value = f"Bearer {self.agent_config.auth_token}"
                 else:
-                    headers[self.agent_config.auth_header] = self.agent_config.auth_token
+                    auth_header_name = self.agent_config.auth_header
+                    auth_value = self.agent_config.auth_token
+                if auth_header_name in headers:
+                    logger.warning(
+                        "extra_headers contains %r which conflicts with auth header; "
+                        "auth_token wins",
+                        auth_header_name,
+                    )
+                headers[auth_header_name] = auth_value
 
             # When ADCPClient installed a signing_request_hook, register it as
             # an httpx request event hook so RFC 9421 signature headers are
diff --git a/src/adcp/protocols/mcp.py b/src/adcp/protocols/mcp.py
index a88167de5..54c4902d4 100644
--- a/src/adcp/protocols/mcp.py
+++ b/src/adcp/protocols/mcp.py
@@ -340,15 +340,22 @@ async def _get_session(self) -> ClientSession:
             self._exit_stack = AsyncExitStack()
 
             # Create SSE client with authentication header
-            headers = {}
+            headers: dict[str, str] = {}
+            if self.agent_config.extra_headers:
+                headers.update(self.agent_config.extra_headers)
             if self.agent_config.auth_token:
-                # Support custom auth headers and types
-                if self.agent_config.auth_type == "bearer":
-                    headers[self.agent_config.auth_header] = (
-                        f"Bearer {self.agent_config.auth_token}"
+                # Support custom auth headers and types; auth always wins on conflict
+                auth_header_name = self.agent_config.auth_header
+                if auth_header_name in headers:
+                    logger.warning(
+                        "extra_headers contains %r which conflicts with auth_header; "
+                        "auth_token wins",
+                        auth_header_name,
                     )
+                if self.agent_config.auth_type == "bearer":
+                    headers[auth_header_name] = f"Bearer {self.agent_config.auth_token}"
                 else:
-                    headers[self.agent_config.auth_header] = self.agent_config.auth_token
+                    headers[auth_header_name] = self.agent_config.auth_token
 
             # Try the user's exact URL first
             urls_to_try = [self.agent_config.agent_uri]
diff --git a/src/adcp/types/core.py b/src/adcp/types/core.py
index 18a5f7ce9..371408694 100644
--- a/src/adcp/types/core.py
+++ b/src/adcp/types/core.py
@@ -30,6 +30,7 @@ class AgentConfig(BaseModel):
         "streamable_http"  # "streamable_http" (default, modern) or "sse" (legacy fallback)
     )
     debug: bool = False  # Enable debug mode to capture request/response details
+    extra_headers: dict[str, str] | None = None  # Extra request headers (e.g. x-adcp-tenant)
 
     @field_validator("agent_uri")
     @classmethod
@@ -86,6 +87,19 @@ def validate_auth_type(cls, v: str) -> str:
             )
         return v
 
+    @field_validator("extra_headers")
+    @classmethod
+    def validate_extra_headers(cls, v: dict[str, str] | None) -> dict[str, str] | None:
+        """Reject CRLF/null sequences in header names and values (header injection guard)."""
+        if v is None:
+            return v
+        for key, value in v.items():
+            if "\r" in key or "\n" in key or "\x00" in key:
+                raise ValueError(f"header name contains CRLF or null byte: {key!r}")
+            if "\r" in value or "\n" in value or "\x00" in value:
+                raise ValueError(f"header value for {key!r} contains CRLF or null byte")
+        return v
+
 
 class TaskStatus(str, Enum):
     """Task execution status."""
diff --git a/tests/test_cli.py b/tests/test_cli.py
index 56f4fdb49..ba615602a 100644
--- a/tests/test_cli.py
+++ b/tests/test_cli.py
@@ -13,8 +13,8 @@
 
 import pytest
 
-from adcp.__main__ import load_payload, resolve_agent_config
-from adcp.config import save_agent
+from adcp.__main__ import load_payload, parse_header_args, resolve_agent_config
+from adcp.config import get_agent, save_agent
 
 
 class TestCLIBasics:
@@ -465,3 +465,100 @@ def test_check_deprecated_fields_handles_list(self, capsys):
         _check_deprecated_fields(formats)
         captured = capsys.readouterr()
         assert "deprecated" not in captured.err.lower()
+
+
+class TestParseHeaderArgs:
+    """Tests for --header KEY=VALUE parsing."""
+
+    def test_single_header(self):
+        result = parse_header_args(["x-adcp-tenant=acme"])
+        assert result == {"x-adcp-tenant": "acme"}
+
+    def test_repeated_headers(self):
+        result = parse_header_args(["x-adcp-tenant=acme", "x-trace-id=abc"])
+        assert result == {"x-adcp-tenant": "acme", "x-trace-id": "abc"}
+
+    def test_value_contains_equals(self):
+        """Value containing = must not be split at the second =."""
+        result = parse_header_args(["Authorization=Basic dXNlcjpwYXNzd29yZA=="])
+        assert result == {"Authorization": "Basic dXNlcjpwYXNzd29yZA=="}
+
+    def test_none_returns_none(self):
+        assert parse_header_args(None) is None
+
+    def test_empty_list_returns_none(self):
+        assert parse_header_args([]) is None
+
+    def test_missing_equals_exits(self):
+        with pytest.raises(SystemExit):
+            parse_header_args(["x-adcp-tenant"])
+
+    def test_empty_key_exits(self):
+        with pytest.raises(SystemExit):
+            parse_header_args(["=value"])
+
+    def test_crlf_in_key_exits(self):
+        with pytest.raises(SystemExit):
+            parse_header_args(["x-bad\r\nkey=value"])
+
+    def test_null_in_value_exits(self):
+        with pytest.raises(SystemExit):
+            parse_header_args(["x-key=val\x00ue"])
+
+
+class TestExtraHeadersSaveLoad:
+    """Tests for extra_headers persistence in config.json."""
+
+    def test_save_agent_persists_extra_headers(self, tmp_path, monkeypatch):
+        config_file = tmp_path / "config.json"
+        config_file.write_text(json.dumps({"agents": {}}))
+
+        import adcp.config
+
+        monkeypatch.setattr(adcp.config, "CONFIG_FILE", config_file)
+
+        save_agent(
+            "local",
+            "http://localhost:8000/mcp",
+            "mcp",
+            "tok",
+            {"x-adcp-tenant": "acme"},
+        )
+
+        raw = json.loads(config_file.read_text())
+        assert raw["agents"]["local"]["extra_headers"] == {"x-adcp-tenant": "acme"}
+
+    def test_get_agent_returns_extra_headers(self, tmp_path, monkeypatch):
+        config_data = {
+            "agents": {
+                "local": {
+                    "agent_uri": "http://localhost:8000/mcp",
+                    "protocol": "mcp",
+                    "extra_headers": {"x-adcp-tenant": "acme"},
+                }
+            }
+        }
+        config_file = tmp_path / "config.json"
+        config_file.write_text(json.dumps(config_data))
+
+        import adcp.config
+
+        monkeypatch.setattr(adcp.config, "CONFIG_FILE", config_file)
+
+        agent = get_agent("local")
+        assert agent is not None
+        assert agent["extra_headers"] == {"x-adcp-tenant": "acme"}
+
+    def test_save_agent_without_extra_headers(self, tmp_path, monkeypatch):
+        """Agents saved without extra_headers should not have the key in config."""
+        config_file = tmp_path / "config.json"
+        config_file.write_text(json.dumps({"agents": {}}))
+
+        import adcp.config
+
+        monkeypatch.setattr(adcp.config, "CONFIG_FILE", config_file)
+
+        save_agent("bare", "http://localhost:8000/mcp", "mcp")
+
+        raw = json.loads(config_file.read_text())
+        assert "extra_headers" not in raw["agents"]["bare"]
diff --git a/tests/test_client.py b/tests/test_client.py
index f1a283d5e..6c5a007e8 100644
--- a/tests/test_client.py
+++ b/tests/test_client.py
@@ -20,6 +20,75 @@ def test_agent_config_creation():
     assert config.protocol == Protocol.A2A
 
 
+def test_agent_config_extra_headers():
+    """AgentConfig accepts extra_headers and stores as dict."""
+    config = AgentConfig(
+        id="test",
+        agent_uri="https://agent.example.com",
+        protocol=Protocol.MCP,
+        extra_headers={"x-adcp-tenant": "acme", "x-trace-id": "abc123"},
+    )
+    assert config.extra_headers == {"x-adcp-tenant": "acme", "x-trace-id": "abc123"}
+    assert config.extra_headers is not None
+
+
+def test_agent_config_extra_headers_default_none():
+    """extra_headers defaults to None."""
+    config = AgentConfig(
+        id="test",
+        agent_uri="https://agent.example.com",
+        protocol=Protocol.MCP,
+    )
+    assert config.extra_headers is None
+
+
+def test_agent_config_extra_headers_roundtrip():
+    """extra_headers survives model_dump / model_validate round-trip as plain dict."""
+    config = AgentConfig(
+        id="rt",
+        agent_uri="https://agent.example.com",
+        protocol=Protocol.MCP,
+        extra_headers={"x-adcp-tenant": "t1"},
+    )
+    dumped = config.model_dump()
+    restored = AgentConfig.model_validate(dumped)
+    assert restored.extra_headers == {"x-adcp-tenant": "t1"}
+    assert isinstance(restored.extra_headers, dict)
+
+
+def test_agent_config_extra_headers_crlf_key_rejected():
+    """extra_headers validator rejects CRLF in header names."""
+    with pytest.raises(Exception, match="CRLF or null"):
+        AgentConfig(
+            id="test",
+            agent_uri="https://agent.example.com",
+            protocol=Protocol.MCP,
+            extra_headers={"x-bad\r\nkey": "value"},
+        )
+
+
+def test_agent_config_extra_headers_crlf_value_rejected():
+    """extra_headers validator rejects CRLF in header values."""
+    with pytest.raises(Exception, match="CRLF or null"):
+        AgentConfig(
+            id="test",
+            agent_uri="https://agent.example.com",
+            protocol=Protocol.MCP,
+            extra_headers={"x-ok-key": "bad\nvalue"},
+        )
+
+
+def test_agent_config_extra_headers_null_byte_rejected():
+    """extra_headers validator rejects null bytes (matching webhooks.py _HEADER_FORBIDDEN_CHARS)."""
+    with pytest.raises(Exception, match="CRLF or null"):
+        AgentConfig(
+            id="test",
+            agent_uri="https://agent.example.com",
+            protocol=Protocol.MCP,
+            extra_headers={"x-ok-key": "val\x00ue"},
+        )
+
+
 def test_client_creation():
     """Test creating ADCP client."""
     config = AgentConfig(