Amazon Bedrock Opus 4.6 compaction failure

[inventumamet]

Description

Got error

undefined: The model returned the following errors: messages.3.content.47: thinking or redacted_thinking blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response.

Plugins

No response

OpenCode version

1.2.6

Steps to reproduce

1. Use Claude Opus 4.6 from Amazon with thinking mode turned on using ctrl+t to select variant (i found that using the non-thinking variant avoids this issue)
2. Use until token is over 170k
3. Try to compact, and the error appears
   undefined: The model returned the following errors: messages.3.content.47: thinking or redacted_thinking blocks in the latest assistant message cannot be modified. These blocks must remain as they were in the original response.
4. Compaction not able to proceed
5. WORKAROUND: Switch to another model on bedrock say Minimax M2, compact works okay, then switch back to Opus 4.6 it will work

Screenshot and/or share link

No response

Operating System

macOS 26.3

Terminal

Zsh (vscode)

[github-actions]

This issue might be a duplicate of existing issues. Please check:

• Claude Opus 4.5 (latest) eventually fails: thinking block cannot be modified #13286: Same exact error — thinking or redacted_thinking blocks cannot be modified — reported for Claude Opus 4.5 with the same root cause (thinking block preservation during message reconstruction/compaction). The difference here is the model (Opus 4.6 via Amazon Bedrock) and the specific trigger (compaction at ~170k tokens), but the underlying bug appears to be the same.

Please review #13286 and consider whether this is the same issue or a related variant specific to Bedrock/compaction flow.

[neshreve]

Also experiencing this behavior on OpenCode 1.2.15, Claude Sonnet 4.6 via AWS Bedrock

[inventumamet]

I haven't had any issues with 1.2.15 so far with opus 4.6. I thought it had been fixed 😁

[bbartels]

Running into this issue with 1.4.7

[rekram1-node]

Is anyone still having this issue? if so can u send me a session: opencode export > session.json run this command NOT /export and send me json file, u can also dm it on X or discord, or email me

[IgnisDa]

Hi @rekram1-node ! I have sent you the export on X.com. If you want I can also email it to you (i couldn't find your email ID, and the discord link in your github profile is invalid).

I have observed the same issue in sonnet-4.6 on bedrock and opus so the export I sent to you was for sonnet. If needed, I can also send you an opus export since the issue is very easy to reproduce.