diff --git a/server/services/assistant_chat_session.py b/server/services/assistant_chat_session.py
index b0051b8..a7f00ca 100755
--- a/server/services/assistant_chat_session.py
+++ b/server/services/assistant_chat_session.py
@@ -255,10 +255,14 @@ class AssistantChatSession:
         # Build environment overrides for API configuration
         sdk_env = {var: os.getenv(var) for var in API_ENV_VARS if os.getenv(var)}
 
+        # Determine model from environment or use default
+        # This allows using alternative APIs (e.g., GLM via z.ai) that may not support Claude model names
+        model = os.getenv("ANTHROPIC_DEFAULT_OPUS_MODEL", "claude-opus-4-5-20251101")
+
         try:
             self.client = ClaudeSDKClient(
                 options=ClaudeAgentOptions(
-                    model="claude-opus-4-5-20251101",
+                    model=model,
                     cli_path=system_cli,
                     # System prompt loaded from CLAUDE.md via setting_sources
                     # This avoids Windows command line length limit (~8191 chars)
diff --git a/server/services/expand_chat_session.py b/server/services/expand_chat_session.py
index 71e56bb..3c4008b 100644
--- a/server/services/expand_chat_session.py
+++ b/server/services/expand_chat_session.py
@@ -167,11 +167,15 @@ class ExpandChatSession:
         # Build environment overrides for API configuration
         sdk_env = {var: os.getenv(var) for var in API_ENV_VARS if os.getenv(var)}
 
+        # Determine model from environment or use default
+        # This allows using alternative APIs (e.g., GLM via z.ai) that may not support Claude model names
+        model = os.getenv("ANTHROPIC_DEFAULT_OPUS_MODEL", "claude-opus-4-5-20251101")
+
         # Create Claude SDK client
         try:
             self.client = ClaudeSDKClient(
                 options=ClaudeAgentOptions(
-                    model="claude-opus-4-5-20251101",
+                    model=model,
                     cli_path=system_cli,
                     system_prompt=system_prompt,
                     allowed_tools=[
diff --git a/server/services/spec_chat_session.py b/server/services/spec_chat_session.py
index 1f0d8cc..818179d 100644
--- a/server/services/spec_chat_session.py
+++ b/server/services/spec_chat_session.py
@@ -169,10 +169,14 @@ class SpecChatSession:
         # Build environment overrides for API configuration
         sdk_env = {var: os.getenv(var) for var in API_ENV_VARS if os.getenv(var)}
 
+        # Determine model from environment or use default
+        # This allows using alternative APIs (e.g., GLM via z.ai) that may not support Claude model names
+        model = os.getenv("ANTHROPIC_DEFAULT_OPUS_MODEL", "claude-opus-4-5-20251101")
+
         try:
             self.client = ClaudeSDKClient(
                 options=ClaudeAgentOptions(
-                    model="claude-opus-4-5-20251101",
+                    model=model,
                     cli_path=system_cli,
                     # System prompt loaded from CLAUDE.md via setting_sources
                     # This avoids Windows command line length limit (~8191 chars)