Codex on AWS bedrock bug causing 10x charges

OpenAI's Codex CLI version 0.147.0 lacks explicit cache controls for GPT-5.6 Sol on Amazon Bedrock, causing cache-write tokens to account for about 85% of estimated spend, with 171.94 million cache-write tokens costing an estimated $1,182.09 out of a total $1,386.46 over four days. The GitHub issue #37674 requests adding support for prompt_cache_options and prompt_cache_breakpoint to reduce costs for agentic coding workloads.

- Notifications /login?return to=%2Fopenai%2Fcodex You must be signed in to change notification settings - Fork 16.6k /login?return to=%2Fopenai%2Fcodex 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