fix: Azure DeepSeek structured output returns JSON in reasoning with empty text

[R-Taneja]

Background

A gateway customer reported that structured-output calls to deepseek/deepseek-v4-flash on Azure fail with NoObjectGeneratedError in ~34% of calls: the response is HTTP 200 with valid JSON, but the JSON is entirely in reasoning and text is empty. Direct Azure calls and Fireworks-served calls for the same model do not fail.

Root cause: DeepSeekChatLanguageModel downgrades responseFormat: json to response_format: {type: 'json_object'} with the schema injected into a system message. When reasoning_effort is also set, the Azure DeepSeek deployment misattributes the constrained JSON output to reasoning_content and returns empty content. Verified by direct-to-Azure A/B with otherwise identical request bodies: json_object + reasoning → 0/3 responses with text (one echoed the input messages into reasoning), json_schema + reasoning → 3/3 with proper reasoning and the JSON in content.

Summary

• Add supportsStructuredOutputs to DeepSeekChatConfig. When enabled and a schema is present, send an OpenAI-shaped json_schema response format (strict defaults to true, new strictJsonSchema provider option) and skip the system-message schema injection and its compatibility warning.
• Enable the flag in azure.deepseek(). The native DeepSeek API path is unchanged and keeps json_object.

Manual Verification

• Ran a structured-output request with reasoning: 'high' via azure.deepseek('deepseek-v4-flash') against a real Azure deployment with this fix: reasoning and structured output are both returned correctly.
• Direct-to-Azure A/B described above (0/3 → 3/3 with identical bodies except response_format).
• Linked the built @ai-sdk/azure + @ai-sdk/deepseek packages into a local AI Gateway checkout: a repro that fails 4/4 against the production gateway passes 4/4 against the local gateway running this fix.

Checklist

• All commits are signed (PRs with unsigned commits cannot be merged)
• Tests have been added / updated (for bug fixes / features)
• Documentation has been added / updated (for bug fixes / features)
• A patch changeset for relevant packages has been added (for bug fixes / features - run pnpm changeset in the project root)
• I have reviewed this pull request (self-review)

Future Work

• Backport to the @ai-sdk/azure@2.x/3.x + @ai-sdk/deepseek@1.x/2.x lines used by older gateway protocol versions.

[github-actions]

⚠️ Backport to release-v6.0 created but has conflicts: #17250

[github-actions]

🚀 Published in:

Package	Version
ai	7.0.28 github npm
@ai-sdk/amazon-bedrock	5.0.22 github npm
@ai-sdk/angular	3.0.28 github npm
@ai-sdk/azure	4.0.15 github npm
@ai-sdk/deepseek	3.0.11 github npm
@ai-sdk/google	4.0.16 github npm
@ai-sdk/google-vertex	5.0.20 github npm
@ai-sdk/harness	1.0.33 github npm
@ai-sdk/harness-claude-code	1.0.34 github npm
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@ai-sdk/harness-opencode	1.0.34 github npm
@ai-sdk/harness-pi	1.0.33 github npm
@ai-sdk/langchain	3.0.28 github npm
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@ai-sdk/otel	1.0.28 github npm
@ai-sdk/policy-opa	1.0.28 github npm
@ai-sdk/react	4.0.30 github npm
@ai-sdk/rsc	3.0.28 github npm
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@ai-sdk/svelte	5.0.28 github npm
@ai-sdk/tui	1.0.28 github npm
@ai-sdk/vue	4.0.28 github npm
@ai-sdk/workflow	1.0.28 github npm
@ai-sdk/workflow-harness	1.0.33 github npm