Grok 4.3 reaches Bedrock through a Mantle-only integration path

AWS has made xAI's Grok 4.3 available in Amazon Bedrock, adding xAI as a Bedrock model provider. AWS lists the active model as `xai.grok-4.3`, with a 1 million-token context window, image input, text output, and configurable reasoning. The change is about an additional managed deployment route for that named model, rather than a newly named model version.

The timing helps distinguish the event from a separate model announcement. AWS's concise availability notice is dated June 15, xAI described general availability on June 17, and AWS published a detailed implementation guide on July 16. The later guide uses the same `xai.grok-4.3` identifier and documents how to deploy it, so it is best read as an integration update rather than evidence of a different Grok version.

For applications already written against OpenAI APIs, the practical change is fewer interface edits, but not a drop-in native Bedrock Runtime call. AWS says Grok 4.3 is accessed through the regional `bedrock-mantle` endpoint and can use OpenAI-compatible Chat Completions or Responses APIs after the client base URL and authentication are changed. The model card does not list Bedrock Runtime as a supported endpoint, so teams should validate endpoint routing and credentials before treating this as an ordinary Bedrock migration.

There are operational constraints worth testing before adoption. AWS documents in-Region inference only at launch, without Geo or Global cross-Region options, and its implementation guide gives nonstandard defaults of 0.7 for temperature, 0.95 for top_p, and 131072 for max_completion_tokens. Those details can affect reproducibility when porting prompts or evaluation baselines. xAI's benchmark-leadership statements remain vendor-reported claims, not independent comparative evidence in this story.