Support anthropic partner models

[dhimmel]

The docs imply that partner models (like those published by anthropic) are supported:

python-genai/google/genai/models.py

Lines 5657 to 5665 in d78add3

	For the `model` parameter, supported formats for Vertex AI API include:
	- The Gemini model ID, for example: 'gemini-2.0-flash'
	- The full resource name starts with 'projects/', for example:
	'projects/my-project-id/locations/us-central1/publishers/google/models/gemini-2.0-flash'
	- The partial resource name with 'publishers/', for example:
	'publishers/google/models/gemini-2.0-flash' or
	'publishers/meta/models/llama-3.1-405b-instruct-maas'
	- `/` separated publisher and model name, for example:
	'google/gemini-2.0-flash' or 'meta/llama-3.1-405b-instruct-maas'

However when I try claude sonnet 4 (model info):

from google import genai
client = genai.Client(
    vertexai=True, location='global'
)
response = client.models.generate_content(
    model='publishers/anthropic/models/claude-sonnet-4', contents="Respond with 'okay'."
)
print(response.text)

I get:

ClientError: 404 NOT_FOUND. {'error': {'code': 404, 'message': 'Publisher Model `projects/[project]/locations/global/publishers/anthropic/models/claude-sonnet-4` not found.', 'status': 'NOT_FOUND'}}

If I change location='us-east5' above, I get:

ClientError: 400 FAILED_PRECONDITION. {'error': {'code': 400, 'message': 'claude-sonnet-4 is not supported in the generateContent API.', 'status': 'FAILED_PRECONDITION'}}

Does this library intend to support partner models?

This occurred on SDK version 1.24.0

[logan-markewich]

Just want to call out that this is likely also related to #567