[Bug] Persistent 400 "Invalid Argument" error with claude-opus-4-6-thinking model (with and without thinking budget) #1533
Description
I am encountering a persistent 400 Bad Request error with the message "Request contains an invalid argument" when attempting to use the claude-opus-4-6-thinking model via the API.
This happens specifically when using the Vercel AI SDK (Alma client) which sends a tools array definition in the request body.
To Reproduce
Send a POST request to /v1/chat/completions.
Set model to claude-opus-4-6-thinking (or claude-opus-4-6-thinking(31999)).
Include a tools array in the request body (Schema definitions for Function Calling).
Result: The API immediately returns a 400 error.
Expected behavior
The model should accept the tool definitions or gracefully ignore unsupported schema properties, and proceed with the generation/thinking process.
Logs & Error Details
Attempt 1: Using model claude-opus-4-6-thinking
Initially, I received specific validation errors regarding the propertyNames field in the JSON schema, which suggests the upstream provider (Vertex/Google?) does not support this keyword.
JSON
// Error detail example
"message": "Invalid JSON payload received. Unknown name "propertyNames" at 'request.tools[0]...': Cannot find field."
Attempt 2: Using model claude-opus-4-6-thinking(31999)
After removing the tools that used propertyNames (Notion/Godot plugins) and updating the model name to include the thinking budget as suggested in other threads, the detailed error disappeared, but I am still blocked by a generic Invalid Argument error.
Request Info:
HTTP
POST /v1/chat/completions
Content-Type: application/json
User-Agent: ai-sdk/openai-compatible/2.0.1
Request Body (Snippet):
JSON
{
"model": "claude-opus-4-6-thinking(31999)",
"max_tokens": 128000,
"messages": [...],
"tools": [ ... ] // Large array of tools (Bash, File operations, etc.)
}
Response:
JSON
{
"error": {
"code": 400,
"message": "Request contains an invalid argument.",
"status": "INVALID_ARGUMENT"
}
}
Additional Context
Client: Alma (running on Windows)
SDK: ai-sdk/openai-compatible/2.0.1
The payload size is large (~94KB) due to multiple tool definitions.
I have tried disabling the specific tools that caused the propertyNames error, but the generic 400 error persists with the remaining tools.
Is there a specific restriction on the tools schema for the "thinking" models, or is the proxy failing to map the (31999) parameter correctly when tools are present?
