AWS adds schema-constrained outputs for Claude on Bedrock

Amazon Web Services says Amazon Bedrock now supports structured outputs for Anthropic’s Claude models on its bedrock-runtime and bedrock-mantle endpoints, wherever each model is available. Developers can specify a JSON schema for model responses, or use strict tool use to constrain the arguments Claude supplies to a tool.

The change targets a familiar integration problem: language models can return data in formats that are difficult for software to consume reliably. AWS says Bedrock uses constrained decoding to enforce the schema as the model generates tokens, rather than checking the result afterward. It says responses will include required fields, use the specified types and omit fields not allowed by the schema.

That could make the feature useful for applications that extract fields from documents, classify support tickets or pass model-generated arguments to tools. AWS describes uses including contract analysis, customer-record processing and agent workflows. Those are potential applications presented by the company, not results from an independent evaluation in the announcement.

The two mechanisms serve related but distinct purposes: the JSON Schema output format controls the shape of a response, while strict tool use checks tool parameters against a schema. AWS says the latter is available through the bedrock-mantle endpoint and is intended for agentic applications that use server-side tools, including web search and code execution.

The feature is not entirely free of setup trade-offs. Bedrock validates schemas against a supported subset of JSON Schema Draft 2020-12 and compiles a grammar for each new schema; AWS warns that the first request using one may take longer. The company says compiled grammars are cached for 24 hours per account, and that changing a schema’s structure triggers a new compilation.

AWS says structured outputs work with batch inference and, on bedrock-runtime, with cross-Region inference. It also says developers can stream structured responses as typed events. The company’s guidance calls for setting additionalProperties to false on objects and recommends reusing schemas to benefit from the cache.