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Creating a new Project in Windows under DOS results in Failed to intialize Claude Error #8
Description
When creating a new project under Windows you will get a "Failed to initialize Claude: Command failed with exit code 1 (exit code: 1) Error output: Check stderr output for details" error message. In the command line you get a "The command line is too long." message, which is accurate. Windows cannot accept the long prompt being passed to Claude on the command line (the DOS command line limit is like 8k characters).
A suggested possible long term fix is to modify server/services/spec_chat_session.py to pass the prompt to Claude via the file parameter so it can be of any length.
Reacted by sermtech
Activity
crocware commentedon Jan 8, 2026
I have the same error on Windows. I was unable to do anything meaningful after the exit code 1 error.
AMSumo9 commentedon Jan 8, 2026
I can't code AT ALL but Claude Code helped me fix this as follows. It got me into the spec chat......
Fix: Spec creation fails on Windows with "command line is too long" error
Problem:
On Windows, creating a new project with Claude spec creation fails immediately with:
The command line is too long.
Fatal error in message reader: Command failed with exit code 1
Failed to initialize Claude: ProcessError
Cause:
Windows has a ~8191 character limit for command-line arguments. The ClaudeSDKClient passes system_prompt via CLI args. In spec_chat_session.py, the entire create-spec.md skill file (~10KB+) was being passed as system_prompt, exceeding this limit.
Linux/macOS aren't affected (they have ~2MB limits).
Fix:
Use a minimal system_prompt for client initialisation (stays under Windows limit)
Send the full skill instructions as the first message via query() (stdin has no size limit)
Files changed:
server/services/spec_chat_session.py - Main fix
client.py - Added documentation about the pattern for future reference
Here's the detailed code changes:
File 1: server/services/spec_chat_session.py
Before (lines 141-167):
project_path = str(self.project_dir.resolve())
system_prompt = skill_content.replace("$ARGUMENTS", project_path)
Create Claude SDK client...
self.client = ClaudeSDKClient(
options=ClaudeAgentOptions(
model="claude-opus-4-5-20251101",
cli_path=system_cli,
system_prompt=system_prompt, # <-- PROBLEM: full skill file here
...
)
)
Start the conversation
async for chunk in self._query_claude("Begin the spec creation process."):
yield chunk
After:
project_path = str(self.project_dir.resolve())
Windows has ~8191 char limit for command-line arguments. The full skill content
passed as system_prompt exceeds this. Solution: use minimal system prompt for
initialization, then send full instructions as first message via stdin (no limit).
minimal_system_prompt = "You are an expert software architect helping create application specifications."
full_skill_instructions = skill_content.replace("$ARGUMENTS", project_path)
Create Claude SDK client...
self.client = ClaudeSDKClient(
options=ClaudeAgentOptions(
model="claude-opus-4-5-20251101",
cli_path=system_cli,
system_prompt=minimal_system_prompt, # <-- FIX: minimal prompt
...
)
)
Start the conversation:
1. Send full skill instructions as first message (via stdin - no size limit)
2. Then begin the spec creation process
async for _ in self._query_claude(full_skill_instructions):
pass # Consume but don't forward - this is just context setting
async for chunk in self._query_claude("Begin the spec creation process."):
yield chunk
File 2: client.py (documentation only)
Added this header comment:
"""
IMPORTANT - Windows Command-Line Limit:
Windows has ~8191 character limit for command-line arguments. The ClaudeSDKClient
passes system_prompt via CLI args, so keep system_prompt SHORT (<2000 chars).
If you need to pass large instructions (e.g., skill files), use this pattern:
See spec_chat_session.py for an example of this pattern.
"""
CoreAspectStu commentedon Jan 12, 2026
before i saw this i also resolved in a similar way, here is my resolution in the community: https://www.skool.com/agentic-labs/autocoder-issue-with-windows?p=bd572de3
You are fixing:
Find this file: subprocess_cli.py
structure \autocoder\venv\Lib\site-packages\claude_agent_sdk_internal\transport
replace with the attached file and try again to run the start_ui.bat file.
subprocess_cli.py
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