## What happened

`AmazonAnthropicClaudeConfig.map_openai_params` in `litellm/llms/bedrock/chat/invoke_transformations/anthropic_claude3_transformation.py` (OSS 1.91.0, lines 76-104) contains a blanket workaround that renames the model to `claude-3-sonnet-20240229` whenever `response_format` appears in params. This forces the tool-based JSON shaping path for every Claude model on the Bedrock Invoke route, including modern Claude 4 models like `anthropic.claude-opus-4-6-v1` and `anthropic.claude-sonnet-4-6` that AWS has enabled native `output_format` support for.

A compounding issue is in `litellm/anthropic_beta_headers_config.json` (the `"bedrock"` section), where `structured-outputs-2025-11-13` is set to `null`. On Bedrock Invoke, Anthropic beta flags flow through the JSON request body as the `anthropic_beta` list. Setting the flag to `null` causes `filter_and_transform_beta_headers` to silently drop it, so even if native `output_format` were passed, the required beta signal would never reach the inference endpoint.

Together these two bugs mean every Bedrock Invoke structured-output request travels the tool-call emulation path regardless of model support, and the beta flag requi…