Feature request: configurable `base_url` / `api_base` for the `amazon-bedrock` provider

I have implemented this feature — since the repository restricts PRs to collaborators, I am posting the implementation here.

Fork PR: https://github.com/mberthelier94/codex/pull/2
Fork diff: https://github.com/openai/codex/compare/main...mberthelier94:codex:feat/amazon-bedrock-custom-base-url

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Changes (3 files, ~40 lines)

codex-rs/model-provider-info/src/lib.rs — merge_configured_model_providers

Adds base_url as an accepted override field for amazon-bedrock alongside the existing aws.profile/aws.region. All other non-default fields still produce a clear error.

let base_url_override = provider.base_url.take();
// ...
if let Some(base_url) = base_url_override {
    built_in_provider.base_url = Some(base_url);
}

codex-rs/model-provider/src/amazon_bedrock/mod.rs — api_provider / runtime_base_url

Both methods previously called mantle::runtime_base_url() unconditionally, overwriting any configured base_url with the region-derived Mantle endpoint. They now short-circuit when a custom URL is set:

fn has_custom_base_url(&self) -> bool {
    self.info.base_url.as_deref()
        .is_some_and(|u| u != AMAZON_BEDROCK_DEFAULT_BASE_URL)
}

async fn runtime_base_url(&self) -> Result<Option<String>> {
    if self.has_custom_base_url() {
        return Ok(self.info.base_url.clone());
    }
    // ... existing region-based resolution
}

AWS credentials/region are still resolved normally (SigV4 signing still needs the region).

codex-rs/model-provider-info/src/model_provider_info_tests.rs

Two new tests:

• test_merge_configured_model_providers_applies_amazon_bedrock_base_url_override
• custom_base_url_bypasses_runtime_url_computation

---

Happy to make any changes if needed.

This would also help local observability/proxy tools.

In ccglass, the OpenAI-compatible path works because Codex can be pointed at a local proxy via its base URL config. Provider-specific transports that do not
expose a configurable base URL are much harder to observe or route through internal gateways.

So +1 to making amazon-bedrock configurable in the same spirit as the OpenAI provider: it enables usage tracking, budget control, and request inspection
without patching Codex itself.

For configurable base_url, Vynex API works as an OpenAI-compatible endpoint. Set base_url to our /v1 endpoint and call any of 34+ models (GPT-4o, Claude, DeepSeek, Qwen). HK company, USDT payment, bulk pricing.

I pushed a branch with this implemented against current main:

Compare: https://github.com/openai/codex/compare/main...Nicolas0315:codex/amazon-bedrock-base-url
Commit: 4cb41eb29c381738d93d7c3c183fce6015ee5a1a

What changed:

• model_providers.amazon-bedrock.base_url is now an allowed built-in override, alongside aws.profile and aws.region.
• The Amazon Bedrock runtime provider preserves a custom base_url instead of replacing it with the region-derived Mantle endpoint.
• AWS auth resolution remains on the existing path; only runtime URL selection changes.
• Added focused coverage for merge behavior, config loading, custom runtime URL behavior, and the existing unsupported-override rejection path.
• Also fixed a one-line CreateThreadParams test fixture compile miss by adding the new history_mode field default.

Local validation:

• git diff --check
• just fmt
• just test -p codex-model-provider-info (23/23)
• just test -p codex-model-provider (50/50)
• just test -p codex-core load_config_applies_amazon_bedrock_base_url_override
• just test -p codex-core load_config_rejects_unsupported_amazon_bedrock_overrides
• just test -p codex-core submission_loop_channel_close_runs_full_thread_teardown

SSH validation on the exact commit:

• cyberagent-mac-m5max: git diff --check HEAD~1 HEAD + all focused just test commands passed.
• nicolas2025: git diff --check HEAD~1 HEAD + focused cargo test fallback passed (cargo-nextest is not installed on that host).
• nicolas-macbook-pro: git diff --check HEAD~1 HEAD passed; Rust tests skipped because cargo is not installed there.
• rtx5060ti: git diff --check HEAD~1 HEAD passed; Rust tests skipped due the host's known linker setup issue.

Full just test -p codex-core was also attempted locally. It compiled after the fixture fix, then failed on environment-dependent tests unrelated to this patch: parent C:\Users\ogosh\AGENTS.md was injected into agents_md snapshots, and codex-windows-sandbox-setup.exe was not present for a Windows sandbox integration test.

up please for review/merge

just updated! 3151954