diff --git a/agent/auxiliary_client.py b/agent/auxiliary_client.py
index 55199e9b9..50d4d86af 100644
--- a/agent/auxiliary_client.py
+++ b/agent/auxiliary_client.py
@@ -48,7 +48,7 @@ from openai import OpenAI
 from agent.credential_pool import load_pool
 from hermes_cli.config import get_hermes_home
 from hermes_constants import OPENROUTER_BASE_URL
-from utils import base_url_hostname
+from utils import base_url_host_matches, base_url_hostname
 
 logger = logging.getLogger(__name__)
 
@@ -817,9 +817,9 @@ def _resolve_api_key_provider() -> Tuple[Optional[OpenAI], Optional[str]]:
                 if is_native_gemini_base_url(base_url):
                     return GeminiNativeClient(api_key=api_key, base_url=base_url), model
             extra = {}
-            if "api.kimi.com" in base_url.lower():
+            if base_url_host_matches(base_url, "api.kimi.com"):
                 extra["default_headers"] = {"User-Agent": "KimiCLI/1.30.0"}
-            elif "api.githubcopilot.com" in base_url.lower():
+            elif base_url_host_matches(base_url, "api.githubcopilot.com"):
                 from hermes_cli.models import copilot_default_headers
 
                 extra["default_headers"] = copilot_default_headers()
@@ -843,9 +843,9 @@ def _resolve_api_key_provider() -> Tuple[Optional[OpenAI], Optional[str]]:
             if is_native_gemini_base_url(base_url):
                 return GeminiNativeClient(api_key=api_key, base_url=base_url), model
         extra = {}
-        if "api.kimi.com" in base_url.lower():
+        if base_url_host_matches(base_url, "api.kimi.com"):
             extra["default_headers"] = {"User-Agent": "KimiCLI/1.30.0"}
-        elif "api.githubcopilot.com" in base_url.lower():
+        elif base_url_host_matches(base_url, "api.githubcopilot.com"):
             from hermes_cli.models import copilot_default_headers
 
             extra["default_headers"] = copilot_default_headers()
@@ -994,7 +994,7 @@ def _resolve_custom_runtime() -> Tuple[Optional[str], Optional[str], Optional[st
         return None, None, None
 
     custom_base = custom_base.strip().rstrip("/")
-    if "openrouter.ai" in custom_base.lower():
+    if base_url_host_matches(custom_base, "openrouter.ai"):
         # requested='custom' falls back to OpenRouter when no custom endpoint is
         # configured. Treat that as "no custom endpoint" for auxiliary routing.
         return None, None, None
@@ -1433,14 +1433,14 @@ def _to_async_client(sync_client, model: str):
         "api_key": sync_client.api_key,
         "base_url": str(sync_client.base_url),
     }
-    base_lower = str(sync_client.base_url).lower()
-    if "openrouter" in base_lower:
+    sync_base_url = str(sync_client.base_url)
+    if base_url_host_matches(sync_base_url, "openrouter.ai"):
         async_kwargs["default_headers"] = dict(_OR_HEADERS)
-    elif "api.githubcopilot.com" in base_lower:
+    elif base_url_host_matches(sync_base_url, "api.githubcopilot.com"):
         from hermes_cli.models import copilot_default_headers
 
         async_kwargs["default_headers"] = copilot_default_headers()
-    elif "api.kimi.com" in base_lower:
+    elif base_url_host_matches(sync_base_url, "api.kimi.com"):
         async_kwargs["default_headers"] = {"User-Agent": "KimiCLI/1.30.0"}
     return AsyncOpenAI(**async_kwargs), model
 
@@ -1621,9 +1621,9 @@ def resolve_provider_client(
                 provider,
             )
             extra = {}
-            if "api.kimi.com" in custom_base.lower():
+            if base_url_host_matches(custom_base, "api.kimi.com"):
                 extra["default_headers"] = {"User-Agent": "KimiCLI/1.30.0"}
-            elif "api.githubcopilot.com" in custom_base.lower():
+            elif base_url_host_matches(custom_base, "api.githubcopilot.com"):
                 from hermes_cli.models import copilot_default_headers
                 extra["default_headers"] = copilot_default_headers()
             client = OpenAI(api_key=custom_key, base_url=custom_base, **extra)
@@ -1728,9 +1728,9 @@ def resolve_provider_client(
 
         # Provider-specific headers
         headers = {}
-        if "api.kimi.com" in base_url.lower():
+        if base_url_host_matches(base_url, "api.kimi.com"):
             headers["User-Agent"] = "KimiCLI/1.30.0"
-        elif "api.githubcopilot.com" in base_url.lower():
+        elif base_url_host_matches(base_url, "api.githubcopilot.com"):
             from hermes_cli.models import copilot_default_headers
 
             headers.update(copilot_default_headers())
@@ -2154,7 +2154,7 @@ def cleanup_stale_async_clients() -> None:
 
 def _is_openrouter_client(client: Any) -> bool:
     for obj in (client, getattr(client, "_client", None), getattr(client, "client", None)):
-        if obj and "openrouter" in str(getattr(obj, "base_url", "") or "").lower():
+        if obj and base_url_host_matches(str(getattr(obj, "base_url", "") or ""), "openrouter.ai"):
             return True
     return False
 
diff --git a/agent/model_metadata.py b/agent/model_metadata.py
index 84cd553c3..47f9bba94 100644
--- a/agent/model_metadata.py
+++ b/agent/model_metadata.py
@@ -14,7 +14,7 @@ from urllib.parse import urlparse
 import requests
 import yaml
 
-from utils import base_url_hostname
+from utils import base_url_host_matches, base_url_hostname
 
 from hermes_constants import OPENROUTER_MODELS_URL
 
@@ -220,7 +220,7 @@ def _auth_headers(api_key: str = "") -> Dict[str, str]:
 
 
 def _is_openrouter_base_url(base_url: str) -> bool:
-    return "openrouter.ai" in _normalize_base_url(base_url).lower()
+    return base_url_host_matches(base_url, "openrouter.ai")
 
 
 def _is_custom_endpoint(base_url: str) -> bool:
@@ -1089,7 +1089,11 @@ def get_model_context_length(
     # 4b. AWS Bedrock — use static context length table.
     # Bedrock's ListFoundationModels doesn't expose context window sizes,
     # so we maintain a curated table in bedrock_adapter.py.
-    if provider == "bedrock" or (base_url and "bedrock-runtime" in base_url):
+    if provider == "bedrock" or (
+        base_url
+        and base_url_hostname(base_url).startswith("bedrock-runtime.")
+        and base_url_host_matches(base_url, "amazonaws.com")
+    ):
         try:
             from agent.bedrock_adapter import get_bedrock_context_length
             return get_bedrock_context_length(model)
diff --git a/agent/usage_pricing.py b/agent/usage_pricing.py
index 29c75b172..3554c5b99 100644
--- a/agent/usage_pricing.py
+++ b/agent/usage_pricing.py
@@ -6,6 +6,7 @@ from decimal import Decimal
 from typing import Any, Dict, Literal, Optional
 
 from agent.model_metadata import fetch_endpoint_model_metadata, fetch_model_metadata
+from utils import base_url_host_matches
 
 DEFAULT_PRICING = {"input": 0.0, "output": 0.0}
 
@@ -393,7 +394,7 @@ def resolve_billing_route(
 
     if provider_name == "openai-codex":
         return BillingRoute(provider="openai-codex", model=model, base_url=base_url or "", billing_mode="subscription_included")
-    if provider_name == "openrouter" or "openrouter.ai" in base:
+    if provider_name == "openrouter" or base_url_host_matches(base_url or "", "openrouter.ai"):
         return BillingRoute(provider="openrouter", model=model, base_url=base_url or "", billing_mode="official_models_api")
     if provider_name == "anthropic":
         return BillingRoute(provider="anthropic", model=model.split("/")[-1], base_url=base_url or "", billing_mode="official_docs_snapshot")
diff --git a/cli.py b/cli.py
index 15f60aa30..68243946f 100644
--- a/cli.py
+++ b/cli.py
@@ -74,6 +74,7 @@ _COMMAND_SPINNER_FRAMES = ("⠋", "⠙", "⠹", "⠸", "⠼", "⠴", "⠦", "⠧
 # User-managed env files should override stale shell exports on restart.
 from hermes_constants import get_hermes_home, display_hermes_home
 from hermes_cli.env_loader import load_hermes_dotenv
+from utils import base_url_host_matches
 
 _hermes_home = get_hermes_home()
 _project_env = Path(__file__).parent / '.env'
@@ -1836,7 +1837,7 @@ class HermesCLI:
         # Match key to resolved base_url: OpenRouter URL → prefer OPENROUTER_API_KEY,
         # custom endpoint → prefer OPENAI_API_KEY (issue #560).
         # Note: _ensure_runtime_credentials() re-resolves this before first use.
-        if self.base_url and "openrouter.ai" in self.base_url:
+        if self.base_url and base_url_host_matches(self.base_url, "openrouter.ai"):
             self.api_key = api_key or os.getenv("OPENROUTER_API_KEY") or os.getenv("OPENAI_API_KEY")
         else:
             self.api_key = api_key or os.getenv("OPENAI_API_KEY") or os.getenv("OPENROUTER_API_KEY")
@@ -4996,7 +4997,7 @@ class HermesCLI:
                 pass
 
         cache_enabled = (
-            ("openrouter" in (result.base_url or "").lower() and "claude" in result.new_model.lower())
+            (base_url_host_matches(result.base_url or "", "openrouter.ai") and "claude" in result.new_model.lower())
             or result.api_mode == "anthropic_messages"
         )
         if cache_enabled:
@@ -5224,7 +5225,7 @@ class HermesCLI:
 
         # Cache notice
         cache_enabled = (
-            ("openrouter" in (result.base_url or "").lower() and "claude" in result.new_model.lower())
+            (base_url_host_matches(result.base_url or "", "openrouter.ai") and "claude" in result.new_model.lower())
             or result.api_mode == "anthropic_messages"
         )
         if cache_enabled:
diff --git a/gateway/run.py b/gateway/run.py
index 3fba1d8d9..6ce409ff1 100644
--- a/gateway/run.py
+++ b/gateway/run.py
@@ -86,7 +86,7 @@ sys.path.insert(0, str(Path(__file__).parent.parent))
 
 # Resolve Hermes home directory (respects HERMES_HOME override)
 from hermes_constants import get_hermes_home
-from utils import atomic_yaml_write, is_truthy_value
+from utils import atomic_yaml_write, base_url_host_matches, is_truthy_value
 _hermes_home = get_hermes_home()
 
 # Load environment variables from ~/.hermes/.env first.
@@ -5661,7 +5661,7 @@ class GatewayRunner:
 
         # Cache notice
         cache_enabled = (
-            ("openrouter" in (result.base_url or "").lower() and "claude" in result.new_model.lower())
+            (base_url_host_matches(result.base_url or "", "openrouter.ai") and "claude" in result.new_model.lower())
             or result.api_mode == "anthropic_messages"
         )
         if cache_enabled:
diff --git a/hermes_cli/doctor.py b/hermes_cli/doctor.py
index 8247d2591..e16f0bf5e 100644
--- a/hermes_cli/doctor.py
+++ b/hermes_cli/doctor.py
@@ -30,6 +30,7 @@ load_dotenv(PROJECT_ROOT / ".env", override=False, encoding="utf-8")
 
 from hermes_cli.colors import Colors, color
 from hermes_constants import OPENROUTER_MODELS_URL
+from utils import base_url_host_matches
 
 
 _PROVIDER_ENV_HINTS = (
@@ -952,7 +953,7 @@ def run_doctor(args):
                     _base = _to_openai_base_url(_base)
                 _url = (_base.rstrip("/") + "/models") if _base else _default_url
                 _headers = {"Authorization": f"Bearer {_key}"}
-                if "api.kimi.com" in _url.lower():
+                if base_url_host_matches(_base, "api.kimi.com"):
                     _headers["User-Agent"] = "KimiCLI/1.30.0"
                 _resp = httpx.get(
                     _url,
diff --git a/hermes_cli/providers.py b/hermes_cli/providers.py
index ca8b075f5..1764474aa 100644
--- a/hermes_cli/providers.py
+++ b/hermes_cli/providers.py
@@ -23,7 +23,7 @@ import logging
 from dataclasses import dataclass
 from typing import Any, Dict, List, Optional, Tuple
 
-from utils import base_url_hostname
+from utils import base_url_host_matches, base_url_hostname
 
 logger = logging.getLogger(__name__)
 
@@ -441,7 +441,7 @@ def determine_api_mode(provider: str, base_url: str = "") -> str:
             return "anthropic_messages"
         if hostname == "api.openai.com":
             return "codex_responses"
-        if "bedrock-runtime" in url_lower and "amazonaws.com" in url_lower:
+        if hostname.startswith("bedrock-runtime.") and base_url_host_matches(base_url, "amazonaws.com"):
             return "bedrock_converse"
 
     return "chat_completions"
diff --git a/hermes_cli/runtime_provider.py b/hermes_cli/runtime_provider.py
index 8a7b44fa4..3b2b4cab3 100644
--- a/hermes_cli/runtime_provider.py
+++ b/hermes_cli/runtime_provider.py
@@ -29,7 +29,7 @@ from hermes_cli.auth import (
 )
 from hermes_cli.config import get_compatible_custom_providers, load_config
 from hermes_constants import OPENROUTER_BASE_URL
-from utils import base_url_hostname
+from utils import base_url_host_matches, base_url_hostname
 
 
 def _normalize_custom_provider_name(value: str) -> str:
@@ -482,7 +482,7 @@ def _resolve_openrouter_runtime(
     # When hitting a custom endpoint (e.g. Z.ai, local LLM), prefer
     # OPENAI_API_KEY so the OpenRouter key doesn't leak to an unrelated
     # provider (issues #420, #560).
-    _is_openrouter_url = "openrouter.ai" in base_url
+    _is_openrouter_url = base_url_host_matches(base_url, "openrouter.ai")
     if _is_openrouter_url:
         api_key_candidates = [
             explicit_api_key,
diff --git a/run_agent.py b/run_agent.py
index cbda3882e..5ec62a06a 100644
--- a/run_agent.py
+++ b/run_agent.py
@@ -124,7 +124,7 @@ from agent.trajectory import (
     convert_scratchpad_to_think, has_incomplete_scratchpad,
     save_trajectory as _save_trajectory_to_file,
 )
-from utils import atomic_json_write, base_url_hostname, env_var_enabled
+from utils import atomic_json_write, base_url_host_matches, base_url_hostname, env_var_enabled
 
 
 
@@ -845,7 +845,10 @@ class AIAgent:
             self.api_mode = "codex_responses"
         elif self.provider == "xai":
             self.api_mode = "codex_responses"
-        elif (provider_name is None) and "chatgpt.com/backend-api/codex" in self._base_url_lower:
+        elif (provider_name is None) and (
+            self._base_url_hostname == "chatgpt.com"
+            and "/backend-api/codex" in self._base_url_lower
+        ):
             self.api_mode = "codex_responses"
             self.provider = "openai-codex"
         elif (provider_name is None) and self._base_url_hostname == "api.x.ai":
@@ -859,8 +862,12 @@ class AIAgent:
             # use a URL convention ending in /anthropic. Auto-detect these so the
             # Anthropic Messages API adapter is used instead of chat completions.
             self.api_mode = "anthropic_messages"
-        elif self.provider == "bedrock" or "bedrock-runtime" in self._base_url_lower:
-            # AWS Bedrock — auto-detect from provider name or base URL.
+        elif self.provider == "bedrock" or (
+            self._base_url_hostname.startswith("bedrock-runtime.")
+            and base_url_host_matches(self._base_url_lower, "amazonaws.com")
+        ):
+            # AWS Bedrock — auto-detect from provider name or base URL
+            # (bedrock-runtime.<region>.amazonaws.com).
             self.api_mode = "bedrock_converse"
         else:
             self.api_mode = "chat_completions"
@@ -1158,23 +1165,23 @@ class AIAgent:
                     client_kwargs["command"] = self.acp_command
                     client_kwargs["args"] = self.acp_args
                 effective_base = base_url
-                if "openrouter" in effective_base.lower():
+                if base_url_host_matches(effective_base, "openrouter.ai"):
                     client_kwargs["default_headers"] = {
                         "HTTP-Referer": "https://hermes-agent.nousresearch.com",
                         "X-OpenRouter-Title": "Hermes Agent",
                         "X-OpenRouter-Categories": "productivity,cli-agent",
                     }
-                elif "api.githubcopilot.com" in effective_base.lower():
+                elif base_url_host_matches(effective_base, "api.githubcopilot.com"):
                     from hermes_cli.models import copilot_default_headers
 
                     client_kwargs["default_headers"] = copilot_default_headers()
-                elif "api.kimi.com" in effective_base.lower():
+                elif base_url_host_matches(effective_base, "api.kimi.com"):
                     client_kwargs["default_headers"] = {
                         "User-Agent": "KimiCLI/1.30.0",
                     }
-                elif "portal.qwen.ai" in effective_base.lower():
+                elif base_url_host_matches(effective_base, "portal.qwen.ai"):
                     client_kwargs["default_headers"] = _qwen_portal_headers()
-                elif "chatgpt.com" in effective_base.lower():
+                elif base_url_host_matches(effective_base, "chatgpt.com"):
                     from agent.auxiliary_client import _codex_cloudflare_headers
                     client_kwargs["default_headers"] = _codex_cloudflare_headers(api_key)
             else:
@@ -1230,7 +1237,7 @@ class AIAgent:
             # stream tool call arguments token-by-token, keeping the
             # connection alive.
             _effective_base = str(client_kwargs.get("base_url", "")).lower()
-            if "openrouter" in _effective_base and "claude" in (self.model or "").lower():
+            if base_url_host_matches(_effective_base, "openrouter.ai") and "claude" in (self.model or "").lower():
                 headers = client_kwargs.get("default_headers") or {}
                 existing_beta = headers.get("x-anthropic-beta", "")
                 _FINE_GRAINED = "fine-grained-tool-streaming-2025-05-14"
@@ -2328,7 +2335,7 @@ class AIAgent:
 
     def _is_openrouter_url(self) -> bool:
         """Return True when the base URL targets OpenRouter."""
-        return "openrouter" in self._base_url_lower
+        return base_url_host_matches(self._base_url_lower, "openrouter.ai")
 
     def _anthropic_prompt_cache_policy(
         self,
@@ -2363,7 +2370,7 @@ class AIAgent:
 
         base_lower = eff_base_url.lower()
         is_claude = "claude" in eff_model.lower()
-        is_openrouter = "openrouter" in base_lower
+        is_openrouter = base_url_host_matches(eff_base_url, "openrouter.ai")
         is_anthropic_wire = eff_api_mode == "anthropic_messages"
         is_native_anthropic = (
             is_anthropic_wire
@@ -5002,20 +5009,19 @@ class AIAgent:
     def _apply_client_headers_for_base_url(self, base_url: str) -> None:
         from agent.auxiliary_client import _AI_GATEWAY_HEADERS, _OR_HEADERS
 
-        normalized = (base_url or "").lower()
-        if "openrouter" in normalized:
+        if base_url_host_matches(base_url, "openrouter.ai"):
             self._client_kwargs["default_headers"] = dict(_OR_HEADERS)
-        elif "ai-gateway.vercel.sh" in normalized:
+        elif base_url_host_matches(base_url, "ai-gateway.vercel.sh"):
             self._client_kwargs["default_headers"] = dict(_AI_GATEWAY_HEADERS)
-        elif "api.githubcopilot.com" in normalized:
+        elif base_url_host_matches(base_url, "api.githubcopilot.com"):
             from hermes_cli.models import copilot_default_headers
 
             self._client_kwargs["default_headers"] = copilot_default_headers()
-        elif "api.kimi.com" in normalized:
+        elif base_url_host_matches(base_url, "api.kimi.com"):
             self._client_kwargs["default_headers"] = {"User-Agent": "KimiCLI/1.30.0"}
-        elif "portal.qwen.ai" in normalized:
+        elif base_url_host_matches(base_url, "portal.qwen.ai"):
             self._client_kwargs["default_headers"] = _qwen_portal_headers()
-        elif "chatgpt.com" in normalized:
+        elif base_url_host_matches(base_url, "chatgpt.com"):
             from agent.auxiliary_client import _codex_cloudflare_headers
             self._client_kwargs["default_headers"] = _codex_cloudflare_headers(
                 self._client_kwargs.get("api_key", "")
@@ -6163,7 +6169,10 @@ class AIAgent:
                 # provider-specific exceptions like Copilot gpt-5-mini on
                 # chat completions.
                 fb_api_mode = "codex_responses"
-            elif fb_provider == "bedrock" or "bedrock-runtime" in fb_base_url.lower():
+            elif fb_provider == "bedrock" or (
+                base_url_hostname(fb_base_url).startswith("bedrock-runtime.")
+                and base_url_host_matches(fb_base_url, "amazonaws.com")
+            ):
                 fb_api_mode = "bedrock_converse"
 
             old_model = self.model
@@ -6596,7 +6605,7 @@ class AIAgent:
 
     def _is_qwen_portal(self) -> bool:
         """Return True when the base URL targets Qwen Portal."""
-        return "portal.qwen.ai" in self._base_url_lower
+        return base_url_host_matches(self._base_url_lower, "portal.qwen.ai")
 
     def _qwen_prepare_chat_messages(self, api_messages: list) -> list:
         prepared = copy.deepcopy(api_messages)
@@ -6717,12 +6726,15 @@ class AIAgent:
                 instructions = DEFAULT_AGENT_IDENTITY
 
             is_github_responses = (
-                "models.github.ai" in self.base_url.lower()
-                or "api.githubcopilot.com" in self.base_url.lower()
+                base_url_host_matches(self.base_url, "models.github.ai")
+                or base_url_host_matches(self.base_url, "api.githubcopilot.com")
             )
             is_codex_backend = (
                 self.provider == "openai-codex"
-                or "chatgpt.com/backend-api/codex" in self.base_url.lower()
+                or (
+                    self._base_url_hostname == "chatgpt.com"
+                    and "/backend-api/codex" in self._base_url_lower
+                )
             )
 
             # Resolve reasoning effort: config > default (medium)
@@ -6923,8 +6935,8 @@ class AIAgent:
 
         _is_openrouter = self._is_openrouter_url()
         _is_github_models = (
-            "models.github.ai" in self._base_url_lower
-            or "api.githubcopilot.com" in self._base_url_lower
+            base_url_host_matches(self._base_url_lower, "models.github.ai")
+            or base_url_host_matches(self._base_url_lower, "api.githubcopilot.com")
         )
 
         # Provider preferences (only, ignore, order, sort) are OpenRouter-
@@ -7000,11 +7012,14 @@ class AIAgent:
         Some providers/routes reject `reasoning` with 400s, so gate it to
         known reasoning-capable model families and direct Nous Portal.
         """
-        if "nousresearch" in self._base_url_lower:
+        if base_url_host_matches(self._base_url_lower, "nousresearch.com"):
             return True
-        if "ai-gateway.vercel.sh" in self._base_url_lower:
+        if base_url_host_matches(self._base_url_lower, "ai-gateway.vercel.sh"):
             return True
-        if "models.github.ai" in self._base_url_lower or "api.githubcopilot.com" in self._base_url_lower:
+        if (
+            base_url_host_matches(self._base_url_lower, "models.github.ai")
+            or base_url_host_matches(self._base_url_lower, "api.githubcopilot.com")
+        ):
             try:
                 from hermes_cli.models import github_model_reasoning_efforts
 
@@ -10566,7 +10581,7 @@ class AIAgent:
                                 self._vprint(f"{self.log_prefix}   💡 Your API key was rejected by the provider. Check:", force=True)
                                 self._vprint(f"{self.log_prefix}      • Is the key valid? Run: hermes setup", force=True)
                                 self._vprint(f"{self.log_prefix}      • Does your account have access to {_model}?", force=True)
-                                if "openrouter" in str(_base).lower():
+                                if base_url_host_matches(str(_base), "openrouter.ai"):
                                     self._vprint(f"{self.log_prefix}      • Check credits: https://openrouter.ai/settings/credits", force=True)
                         else:
                             self._vprint(f"{self.log_prefix}   💡 This type of error won't be fixed by retrying.", force=True)
diff --git a/tests/test_base_url_hostname.py b/tests/test_base_url_hostname.py
index 89842cac2..54aca08c0 100644
--- a/tests/test_base_url_hostname.py
+++ b/tests/test_base_url_hostname.py
@@ -1,13 +1,17 @@
-"""Targeted tests for ``utils.base_url_hostname``.
+"""Targeted tests for ``utils.base_url_hostname`` and ``base_url_host_matches``.
 
-The helper is used across provider routing, auxiliary client, and setup
-wizards to avoid the substring-match false-positive class documented in
+These helpers are used across provider routing, auxiliary client, setup
+wizards, billing routes, and the trajectory compressor to avoid the
+substring-match false-positive class documented in
 tests/agent/test_direct_provider_url_detection.py.
 """
 
 from __future__ import annotations
 
-from utils import base_url_hostname
+from utils import base_url_hostname, base_url_host_matches
+
+
+# ─── base_url_hostname ────────────────────────────────────────────────────
 
 
 def test_empty_returns_empty_string():
@@ -31,18 +35,15 @@ def test_hostname_case_insensitive():
 
 
 def test_trailing_dot_stripped():
-    # Fully-qualified hostnames may include a trailing dot.
     assert base_url_hostname("https://api.openai.com./v1") == "api.openai.com"
 
 
 def test_path_containing_provider_host_is_not_the_hostname():
-    # The key regression — proxy paths must never be misread as the host.
     assert base_url_hostname("https://proxy.example.test/api.openai.com/v1") == "proxy.example.test"
     assert base_url_hostname("https://proxy.example.test/api.anthropic.com/v1") == "proxy.example.test"
 
 
 def test_host_suffix_is_not_the_provider():
-    # A hostname that merely ends with the provider domain is not the provider.
     assert base_url_hostname("https://api.openai.com.example/v1") == "api.openai.com.example"
     assert base_url_hostname("https://api.x.ai.example/v1") == "api.x.ai.example"
 
@@ -53,3 +54,55 @@ def test_port_is_ignored():
 
 def test_whitespace_stripped():
     assert base_url_hostname("  https://api.openai.com/v1  ") == "api.openai.com"
+
+
+# ─── base_url_host_matches ────────────────────────────────────────────────
+
+
+class TestBaseUrlHostMatchesExact:
+    def test_exact_domain_matches(self):
+        assert base_url_host_matches("https://openrouter.ai/api/v1", "openrouter.ai") is True
+        assert base_url_host_matches("https://moonshot.ai", "moonshot.ai") is True
+
+    def test_subdomain_matches(self):
+        # A subdomain of the registered domain should match — needed for
+        # api.moonshot.ai / api.kimi.com / portal.qwen.ai lookups that
+        # accept both the bare registrable domain and any subdomain under it.
+        assert base_url_host_matches("https://api.moonshot.ai/v1", "moonshot.ai") is True
+        assert base_url_host_matches("https://api.kimi.com/v1", "api.kimi.com") is True
+        assert base_url_host_matches("https://portal.qwen.ai/v1", "portal.qwen.ai") is True
+
+
+class TestBaseUrlHostMatchesNegatives:
+    """The reason this helper exists — defend against substring collisions."""
+
+    def test_path_segment_containing_domain_does_not_match(self):
+        assert base_url_host_matches("https://evil.test/moonshot.ai/v1", "moonshot.ai") is False
+        assert base_url_host_matches("https://proxy.example.test/openrouter.ai/v1", "openrouter.ai") is False
+        assert base_url_host_matches("https://proxy/api.kimi.com/v1", "api.kimi.com") is False
+
+    def test_host_suffix_does_not_match(self):
+        # Attacker-controlled hosts that end with the domain string are not
+        # the domain.
+        assert base_url_host_matches("https://moonshot.ai.evil/v1", "moonshot.ai") is False
+        assert base_url_host_matches("https://openrouter.ai.example/v1", "openrouter.ai") is False
+
+    def test_host_prefix_does_not_match(self):
+        # "fake-openrouter.ai" is not a subdomain of openrouter.ai.
+        assert base_url_host_matches("https://fake-openrouter.ai/v1", "openrouter.ai") is False
+
+
+class TestBaseUrlHostMatchesEdgeCases:
+    def test_empty_base_url_returns_false(self):
+        assert base_url_host_matches("", "openrouter.ai") is False
+        assert base_url_host_matches(None, "openrouter.ai") is False  # type: ignore[arg-type]
+
+    def test_empty_domain_returns_false(self):
+        assert base_url_host_matches("https://openrouter.ai/v1", "") is False
+
+    def test_case_insensitive(self):
+        assert base_url_host_matches("https://OpenRouter.AI/v1", "openrouter.ai") is True
+        assert base_url_host_matches("https://openrouter.ai/v1", "OPENROUTER.AI") is True
+
+    def test_trailing_dot_on_domain_stripped(self):
+        assert base_url_host_matches("https://openrouter.ai/v1", "openrouter.ai.") is True
diff --git a/tools/delegate_tool.py b/tools/delegate_tool.py
index 3851bad3f..7065e129a 100644
--- a/tools/delegate_tool.py
+++ b/tools/delegate_tool.py
@@ -1025,7 +1025,10 @@ def _resolve_delegation_credentials(cfg: dict, parent_agent) -> dict:
         base_lower = configured_base_url.lower()
         provider = "custom"
         api_mode = "chat_completions"
-        if "chatgpt.com/backend-api/codex" in base_lower:
+        if (
+            base_url_hostname(configured_base_url) == "chatgpt.com"
+            and "/backend-api/codex" in base_lower
+        ):
             provider = "openai-codex"
             api_mode = "codex_responses"
         elif base_url_hostname(configured_base_url) == "api.anthropic.com":
diff --git a/trajectory_compressor.py b/trajectory_compressor.py
index b0fec6041..ff2dcc626 100644
--- a/trajectory_compressor.py
+++ b/trajectory_compressor.py
@@ -40,6 +40,8 @@ from pathlib import Path
 from typing import List, Dict, Any, Optional, Tuple, Callable
 from dataclasses import dataclass, field
 from datetime import datetime
+
+from utils import base_url_host_matches, base_url_hostname
 import fire
 from rich.progress import Progress, SpinnerColumn, TextColumn, BarColumn, TaskProgressColumn, TimeElapsedColumn, TimeRemainingColumn
 from rich.console import Console
@@ -432,22 +434,29 @@ class TrajectoryCompressor:
 
     def _detect_provider(self) -> str:
         """Detect the provider name from the configured base_url."""
-        url = (self.config.base_url or "").lower()
-        if "openrouter" in url:
+        url = self.config.base_url or ""
+        if base_url_host_matches(url, "openrouter.ai"):
             return "openrouter"
-        if "nousresearch.com" in url:
+        if base_url_host_matches(url, "nousresearch.com"):
             return "nous"
-        if "chatgpt.com/backend-api/codex" in url:
+        if (
+            base_url_hostname(url) == "chatgpt.com"
+            and "/backend-api/codex" in url.lower()
+        ):
             return "codex"
-        if "api.z.ai" in url:
+        if base_url_host_matches(url, "z.ai"):
             return "zai"
-        if "moonshot.ai" in url or "moonshot.cn" in url or "api.kimi.com" in url:
+        if (
+            base_url_host_matches(url, "moonshot.ai")
+            or base_url_host_matches(url, "moonshot.cn")
+            or base_url_host_matches(url, "api.kimi.com")
+        ):
             return "kimi-coding"
-        if "arcee.ai" in url:
+        if base_url_host_matches(url, "arcee.ai"):
             return "arcee"
-        if "minimaxi.com" in url:
+        if base_url_host_matches(url, "minimaxi.com"):
             return "minimax-cn"
-        if "minimax.io" in url:
+        if base_url_host_matches(url, "minimax.io"):
             return "minimax"
         # Unknown base_url — not a known provider
         return ""
diff --git a/utils.py b/utils.py
index 69a18d584..6b998e223 100644
--- a/utils.py
+++ b/utils.py
@@ -216,3 +216,24 @@ def base_url_hostname(base_url: str) -> str:
     parsed = urlparse(raw if "://" in raw else f"//{raw}")
     return (parsed.hostname or "").lower().rstrip(".")
 
+
+def base_url_host_matches(base_url: str, domain: str) -> bool:
+    """Return True when the base URL's hostname is ``domain`` or a subdomain.
+
+    Safer counterpart to ``domain in base_url``, which is the substring
+    false-positive class documented on ``base_url_hostname``. Accepts bare
+    hosts, full URLs, and URLs with paths.
+
+        base_url_host_matches("https://api.moonshot.ai/v1", "moonshot.ai") == True
+        base_url_host_matches("https://moonshot.ai", "moonshot.ai")        == True
+        base_url_host_matches("https://evil.com/moonshot.ai/v1", "moonshot.ai") == False
+        base_url_host_matches("https://moonshot.ai.evil/v1", "moonshot.ai")     == False
+    """
+    hostname = base_url_hostname(base_url)
+    if not hostname:
+        return False
+    domain = (domain or "").strip().lower().rstrip(".")
+    if not domain:
+        return False
+    return hostname == domain or hostname.endswith("." + domain)
+