Are there any foundation model APIs that support model versioning and JSON mode for stable app releases?

Yes. Several foundation model APIs support both model versioning and some form of JSON / structured output mode, which is useful for stable app releases.

Good options

• OpenAI API
  • Versioning: model names are explicit, and newer versions are released under new names or dated snapshots in some cases.
  • JSON mode / structured output: supports JSON mode and newer structured outputs for schema-constrained responses.
• Anthropic API
  • Versioning: model names include versioned identifiers like claude-3-5-sonnet-20240620.
  • JSON mode: supports tool use and structured prompting patterns; depending on the endpoint/features you may still need to validate output carefully.
• Google Gemini API
  • Versioning: model names are versioned, e.g. gemini-1.5-pro.
  • JSON output: supports JSON/schema-style response configuration in supported endpoints.
• AWS Bedrock
  • Versioning: depends on the provider/model; Bedrock exposes specific model IDs and versions.
  • Structured output: often supported through prompt engineering, tool use, or provider-specific features.
• Azure OpenAI
  • Versioning: you choose a model deployment plus a pinned model version in many setups.
  • JSON mode: similar to OpenAI’s capabilities, depending on the deployed model/API version.

What to look for for stable releases

For app stability, prefer APIs that offer:

1. Pinned model IDs or dated versions rather than only “latest”
2. JSON mode or schema-constrained output
3. Deprecation windows / release notes
4. Ability to pin API versions as well as model versions

Practical recommendation

If your priority is stable, machine-readable output, the safest pattern is:

• use a version-pinned model
• enable JSON mode / structured outputs
• add server-side validation for the returned JSON
• keep a fallback path if the provider changes behavior

If you want, I can give you a comparison table of OpenAI vs Anthropic vs Gemini vs Bedrock for version pinning and JSON support.