Codex now appends tool list updates to conversation history by default for developers using Google Cloud Vertex AI. This sends tool list changes without rewriting existing history, requires no setup, and can be disabled.

1. How tool lists are sent is changing

Codex 0.167.2, released by OpenAI on November 11, 2026, adds incremental tool updates for Vertex AI. Tool declarations list and describe the tools available to the model. When the list changes, it is appended rather than rewriting existing records.

According to the pull request adding support, incremental mode sends tool declarations through the additional_tools input rather than the outermost tools array. The request format now sends the tool list as a separate additional input.

Tests covered grouping tools by name, tool search, and command execution tools. The Google Cloud path was also added to a scenario that appends a changed tool list without rewriting prior conversation history.

2. Vertex AI and Bedrock settings operate independently

The follow-up change setting the defaults added the Vertex AI feature as stable for regular Responses requests. The Amazon Bedrock feature also became stable but remained disabled by default. Enabling incremental updates on Vertex AI does not also enable the Bedrock setting.

The original code change separating the two providers' features is shown below. Added lines have a leading plus sign.

     /// Publish incremental tool declarations on regular Amazon Bedrock Responses.
     IncrementalToolsLegacy,
+    /// Publish incremental tool declarations on regular GCP Responses.
+    IncrementalToolsLegacyGcp,

The settings are independent too. Integration tests included enabling and disabling incremental_tools_legacy_gcp for Vertex AI and incremental_tools_legacy for Bedrock in opposite combinations.

3. Less history rewriting, more additional input management

This approach avoids rewriting existing conversation history when the tool list changes. Sending tool updates separately from existing records can reduce the burden of rewriting history in tasks where available tools change along the way.

Developers inspecting requests directly must account for the new location of tool declarations. Environments using multiple providers must also manage their defaults and settings separately. The transmission change offers benefits, but checking request formats and provider-specific settings remains an operational task.

The release notes and two pull requests contain no performance or cost measurements. These sources alone cannot quantify speed improvements or cost savings.

4. The new default can be disabled in settings

The release notes also explain configuration for users who do not want the new behavior. The feature can be disabled under [features] in config.toml.

Set incremental_tools_legacy_gcp = false to disable it. On Vertex AI, users can adopt the new default without adding settings or explicitly disable it as needed.

Codex 0.167.2 switches Vertex AI tool list updates to an approach that appends them to history, while allowing users to choose this behavior separately for each provider.