Prompt too long when using Claude Opus 4.6 (Global) Amazon Bedrock

[shakedlokits]

Description

Issue

I've got the error:

undefined: The model returned the following errors: prompt is too long: 210602 tokens > 200000 maximum

When using the model: Claude Opus 4.6 (Global) Amazon Bedrock

Expected behavior

The context window of Claude Opus 4.6 is 1M tokens and not 200K tokens.

Workaround

Changed model to Claude Opus 4.5 (Global) Amazon Bedrock which triggered compaction.

Plugins

No response

OpenCode version

1.1.53

Steps to reproduce

1. Set the model to Claude Opus 4.6 (Global) Amazon Bedrock
2. Exceed the 200K token limit

Screenshot and/or share link

Operating System

macOS 26.2

Terminal

Ghostty

[github-actions]

This issue appears to be related to existing problems with Claude Opus 4.6 context window configuration. Please check:

• Beta header context-1m-2025-08-07 not sent for Claude Opus 4.6, causing 200k hard limit #12507: Beta header 'context-1m-2025-08-07' not sent for Claude Opus 4.6, causing 200k hard limit — This is the root cause. OpenCode needs to send the proper beta header to unlock the 1M context window.
• fix(zen): 1M context window beta not sent for Opus 4.6 and Sonnet 4.5 #12452: fix(zen): 1M context window beta not sent for Opus 4.6 and Sonnet 4.5 — A proposed fix for the same issue
• Claude Opus 4.6 context window limits still 200k #12438: Claude Opus 4.6 context window limits still 200k — Another user experiencing the same problem even after manual config updates
• Model IDs are wrong for Opus 4.6 on AWS Bedrock #12330: Model IDs are wrong for Opus 4.6 on AWS Bedrock — Potential additional issue with Bedrock model ID configuration

The core issue is that the context-1m-2025-08-07 beta header is not being sent for Opus 4.6 models, which prevents the Anthropic API from allowing requests beyond 200k tokens despite the model supporting 1M tokens.

[Badbird5907]

I'm also getting this issue on Amazon Bedrock

[shakedlokits]

It's not fixed as of 1.2.4, currently cannot use Opus 4.6 on my work laptop.

[smashah]

happening on 4.6 via antigravity auth also.

[LucaNerlich]

Same here. AutoCompaction is either missing or not kicking in. Switching to another model, seems to trigger the compaction, after which one cat switch back to 4.6 etc.