# Codex on AWS bedrock bug causing 10x charges

> Source: <https://github.com/openai/codex/issues/37674>
> Published: 2026-08-21 03:17:43+00:00

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# Native Bedrock Codex GPT-5.6 Sol lacks explicit cache controls, producing high cache-write spend #37674

[CLIIssues related to the Codex CLI](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22CLI%22)Issues related to the Codex CLI

[aws-bedrockIssues related to AWS Bedrock provider](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22aws-bedrock%22)Issues related to AWS Bedrock provider

[enhancementNew feature or request](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22enhancement%22)New feature or request

[rate-limitsIssues related to rate limits, quotas, and token usage reporting](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22rate-limits%22)Issues related to rate limits, quotas, and token usage reporting

## Description

## Summary

Native Codex CLI requests to Amazon Bedrock Mantle cannot opt into GPT-5.6 Sol explicit prompt caching. On an agentic coding workload, this has produced a large volume of cache-write tokens and materially higher cost.

This is related to [#35300](https://github.com/openai/codex/issues/35300), but adds independent production usage evidence from the native `amazon-bedrock`

provider.

## Environment

- Codex CLI:
`0.147.0`

- Provider: native
`amazon-bedrock`

- Endpoint: Bedrock Mantle Responses API,
`us-east-1`

- Model:
`openai.gpt-5.6-sol`

## Observed production usage

For the completed days 2026-08-05 through 2026-08-08, Cost Explorer usage quantities and the Bedrock rate card produced the following cache-aware estimate for Sol:

| Requests | Cache-write tokens | Estimated cache-write cost | Estimated total cost |
|---|---|---|---|
| 3,656 | 171.94M | $1,182.09 | $1,386.46 |

Cache writes were about 85% of the model's estimated spend.

A local Codex session also reported 76 Sol requests with 6.709M `cache_write_input_tokens`

, zero `cached_input_tokens`

, and an average of about 88K cache-write tokens per request. There were no client errors in the corresponding CloudWatch metrics.

These are usage-derived estimates, not finalized AWS invoice amounts.

## Investigation

Codex already emits a session-scoped `prompt_cache_key`

, but the request types for both HTTP and WebSocket Responses requests do not include either:

`prompt_cache_options`

`prompt_cache_breakpoint`

The built-in Amazon Bedrock provider config exposes transport/auth settings, not structured request-body transformation, so this cannot be configured through `config.toml`

.

AWS documents explicit cache mode for GPT-5.6 on Bedrock specifically for agentic workflows with long stable instructions/tool definitions followed by changing tool and user content. That matches the workload above.

## Requested behavior

- Add support for serializing
`prompt_cache_options`

for GPT-5.6-capable Responses providers. - Add a typed
`prompt_cache_breakpoint`

field to supported input content blocks. - Provide a provider/model capability gate and a safe placement strategy at the end of Codex's measured stable instruction/tool prefix.
- Surface cache reads and cache writes in per-turn usage telemetry so users can diagnose costly full-prefix rewrites.

## Scope

This report does not claim that every cache write is a defect. Cold starts, genuinely distinct prompts, forks, and compaction can all require writes. The issue is that native Bedrock Codex currently has no way to use the documented explicit-cache mechanism for the stable-prefix case.

## Metadata

## Metadata

### Assignees

### Labels

[CLIIssues related to the Codex CLI](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22CLI%22)Issues related to the Codex CLI

[aws-bedrockIssues related to AWS Bedrock provider](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22aws-bedrock%22)Issues related to AWS Bedrock provider

[enhancementNew feature or request](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22enhancement%22)New feature or request

[rate-limitsIssues related to rate limits, quotas, and token usage reporting](https://github.com/openai/codex/issues?q=state%3Aopen%20label%3A%22rate-limits%22)Issues related to rate limits, quotas, and token usage reporting