I Found That Claude Fable 5 Can Now Be Called via Bedrock Mantle, So I Tried It Out
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Introduction
In the previous article (7/1), I checked whether Claude Fable 5 could be called from Amazon Bedrock Mantle. At that time, a 404 was returned in every region I checked, and the model did not exist.
When I checked again on 7/5, model information could be retrieved from Mantle. By setting Data Retention Mode, the invocation also succeeded. The differences from the previous check are as follows.
| Item | Previous (7/1) | This time (7/5) |
|---|---|---|
| Model existence in Mantle | 404: model does not exist |
Retrievable via GET /v1/models/{id} |
/anthropic/v1/messages |
Could not be tried (no model) | Succeeded after Data Retention was set |
| OpenAI-compatible paths | Could not be tried (no model) | Not supported (400) |
Verification
In the following verification, I used a token obtained with aws-bedrock-token-generator as the Mantle API key.
pip install aws-bedrock-token-generator
export BEDROCK_API_KEY=$(python -c "from aws_bedrock_token_generator import provide_token; print(provide_token(region='us-east-1'))")
Checking whether the model is available
I checked the model information with GET /v1/models/anthropic.claude-fable-5.
curl https://bedrock-mantle.us-east-1.api.aws/v1/models/anthropic.claude-fable-5 \
-H "x-api-key: $BEDROCK_API_KEY"
{
"id": "anthropic.claude-fable-5",
"object": "model",
"created": 1780272000,
"owned_by": "system",
"status": "unavailable",
"data_retention": {
"allowed_modes": ["provider_data_share"],
"mode": "inherit",
"source": "account"
}
}
status is unavailable, and data_retention.allowed_modes contains only ["provider_data_share"]. If it stays at inherit, the condition is not met and the model cannot be used.
Setting Data Retention Mode
# Check the current setting on the Mantle side
curl https://bedrock-mantle.us-east-1.api.aws/v1/data_retention \
-H "x-api-key: $BEDROCK_API_KEY"
{"mode":"inherit"}
With inherit left as is, the invocation of Fable 5 failed. I will change it to provider_data_share.
# Change the Mantle side to provider_data_share
curl -X PUT https://bedrock-mantle.us-east-1.api.aws/v1/data_retention \
-H "x-api-key: $BEDROCK_API_KEY" \
-H "Content-Type: application/json" \
-d '{"mode": "provider_data_share"}'
{"mode":"provider_data_share","updated_at":1783233083}
As a reference, checking the Data Retention on the Control Plane side with the AWS CLI gives the following.
aws bedrock get-account-data-retention --region us-east-1
{"mode": "provider_data_share", "updatedAt": "2026-06-09T23:46:41.595000+00:00"}
The Control Plane side had already been set on 6/10, but the Mantle side was still inherit. The two are managed separately.
Calling with the Anthropic Messages API
After setting Data Retention, I was able to call Fable 5 via /anthropic/v1/messages.
curl -X POST https://bedrock-mantle.us-east-1.api.aws/anthropic/v1/messages \
-H "x-api-key: $BEDROCK_API_KEY" \
-H "content-type: application/json" \
-H "anthropic-version: 2023-06-01" \
-d '{
"model": "anthropic.claude-fable-5",
"max_tokens": 200,
"messages": [{"role": "user", "content": "Hello!"}]
}'
{
"model": "claude-fable-5",
"id": "msg_bdrk_5b574rbpxs5stk37sqg44r2ecpro4dx4e5zzk65dvap4njpl6xsq",
"type": "message",
"role": "assistant",
"content": [
{
"type": "text",
"text": "Hello! I'm Claude, an AI assistant made by Anthropic, here to help you with questions, writing, analysis, and much more."
}
],
"stop_reason": "end_turn",
"usage": {
"input_tokens": 23,
"output_tokens": 30
}
}
Calling with the Anthropic Python SDK
The Anthropic SDK internally appends the /v1/messages path. If you specify base_url up to Mantle's /anthropic, it calls the same path as in the curl example.
from anthropic import Anthropic
from aws_bedrock_token_generator import provide_token
token = provide_token(region="us-east-1")
client = Anthropic(
api_key=token,
base_url="https://bedrock-mantle.us-east-1.api.aws/anthropic",
)
message = client.messages.create(
model="anthropic.claude-fable-5",
max_tokens=200,
messages=[{"role": "user", "content": "Hello!"}],
)
print(message.content[0].text)
OpenAI-compatible paths are not supported
Fable 5 does not support Mantle's OpenAI-compatible endpoints.
| Path | Result |
|---|---|
/openai/v1/responses |
400: does not support the '/openai/v1/responses' API |
/v1/chat/completions |
400: does not support the '/v1/chat/completions' API |
/openai/v1/chat/completions |
400: does not support the '/openai/v1/chat/completions' API |
All of them return HTTP 400, an error indicating that the model does not support the API path in question (not a 404 for a nonexistent path).
Summary
Claude Fable 5, which did not exist in Mantle as of July 1, could be confirmed via GET /v1/models/anthropic.claude-fable-5 as of July 5.
In this verification environment, changing the Data Retention Mode on the Mantle side to provider_data_share allowed me to call it from /anthropic/v1/messages. Because it is managed separately from the Control Plane's Data Retention setting, you need to check the Mantle-side setting even if you can already use the model through the Converse API.
