> ## Documentation Index
> Fetch the complete documentation index at: https://docs.getbifrost.ai/llms.txt
> Use this file to discover all available pages before exploring further.

# v1.6.6

> v1.6.6 changelog - 2026-07-24

<Tabs>
  <Tab title="NPX">
    ```bash theme={null}
    npx -y @maximhq/bifrost --transport-version v1.6.6
    ```
  </Tab>

  <Tab title="Docker">
    ```bash theme={null}
    docker pull maximhq/bifrost:v1.6.6
    docker run -p 8080:8080 maximhq/bifrost:v1.6.6
    ```
  </Tab>
</Tabs>

<Update label="Bifrost(HTTP)" description="1.6.6">
  # ✨ Features

  * **Anthropic Default Fallback Routing** — Added support for Anthropic's `fallbacks: "default"` preset, preserving it through the Bifrost round-trip and injecting the `server-side-fallback-2026-07-01` beta header for default-routing requests.
  * **Mid-Conversation Tool Changes** — Added support for the `mid-conversation-tool-changes-2026-07-01` beta header, enabled for Anthropic and Bedrock Mantle.

  ## 🐞 Fixed

  * **Opus 5 Compatibility** — Added Opus 5 detection to the Anthropic provider so it inherits Opus 4.8's request surface: `budget_tokens`, `temperature`, `top_p`, and `top_k` are stripped, and native `effort`, fast mode, and mid-conversation system messages are enabled.
</Update>