Anthropic provider sends deprecated `output_format` instead of `output_config.format`, breaking Bedrock structured outputs

[p3droml]

Description

@ai-sdk/anthropic sends the deprecated output_format parameter when using structuredOutputMode: "outputFormat". The Anthropic API has migrated to output_config.format (docs).

The direct Anthropic API still accepts output_format temporarily, but Amazon Bedrock already rejects it:

output_format: This field is deprecated. Use 'output_config.format' instead.
See https://platform.claude.com/docs/en/build-with-claude/structured-outputs for more information.

This means there is currently no way to use structured outputs with thinking/adaptive on Bedrock through the AI SDK, even though the Bedrock API fully supports it via output_config.format.

Root cause

In @ai-sdk/anthropic, the request body is built with the deprecated parameter name:

// @ai-sdk/anthropic/dist/index.mjs ~line 2599
...useStructuredOutput && responseFormat?.type === "json" && responseFormat.schema != null && {
  output_format: {       // <-- deprecated, should be output_config.format
    type: "json_schema",
    schema: responseFormat.schema
  }
},

Additionally, @ai-sdk/amazon-bedrock/anthropic hardcodes supportsNativeStructuredOutput: false with the comment "force the use of JSON tool fallback for structured outputs since beta header isn't supported" — but structured outputs are now GA on Bedrock (no beta header required).

Reproduction

Full reproduction script (3 tests — 2 fail via AI SDK, 1 passes via @anthropic-ai/bedrock-sdk):
https://gist.github.com/p3droml/4b9a903054952a1095a71d88ce10ff4e

npm install ai @ai-sdk/amazon-bedrock @anthropic-ai/bedrock-sdk zod tsx
# Set AWS_REGION, AWS_ACCESS_KEY_ID, AWS_SECRET_ACCESS_KEY
npx tsx test-bedrock-structured-output.ts

Output:

1. AI SDK — bedrock (Converse API)
   ✗ FAILED: Thinking may not be enabled when tool_choice forces tool use.

2. AI SDK — bedrockAnthropic (Invoke API, structuredOutputMode: outputFormat)
   ✗ FAILED: output_format: This field is deprecated. Use 'output_config.format' instead.

3. @anthropic-ai/bedrock-sdk — output_config.format (native SDK)
   Output: { answer: 'Love is a deep emotional bond...' }
   ✓ PASSED

Suggested fix

1. In @ai-sdk/anthropic: rename output_format to output_config.format in the request body
2. In @ai-sdk/amazon-bedrock/anthropic: set supportsNativeStructuredOutput: true (structured outputs are GA on Bedrock, no beta header needed)

AI SDK Version

• ai: 6.0.72
• @ai-sdk/anthropic: 3.0.37
• @ai-sdk/amazon-bedrock: 4.0.49
• @anthropic-ai/bedrock-sdk: 0.26.3 (used to verify Bedrock API works)

[muraliavarma]

I got a quick PR for this out: #12319 I hope this is reasonable, but happy to change it if needed.

[ZinoKader]

Bedrock has gone GA with this feature. Sonnet 4.5 and Haiku 4.5 have now both supported this for more than a month. Quite appropriate to move this forward so reliable structured outputs are available thorugh the Vercel AI SDK.

🚀 Published in:

Package	Version
@ai-sdk/amazon-bedrock	4.0.68
@ai-sdk/anthropic	3.0.49
@ai-sdk/google-vertex	4.0.67