[BUG] thinking.adaptive.block_binding.prefix_mismatch_behavior: Extra inputs are not permitted

Description

After upgrading from OpenCode 1.18.25 to 1.18.26, requests to amazon-bedrock/global.anthropic.claude-opus-5 fail before producing output:

The model returned the following errors: thinking.adaptive.block_binding.prefix_mismatch_behavior: Extra inputs are not permitted

The same Bedrock model and configuration worked before 1.18.26. There is no custom thinking or reasoningConfig override.

1.18.26 introduced block_binding for Claude 5 in #46653. That PR notes that live verification against Bedrock was still outstanding. The Bedrock Opus 5 route appears to reject the injected field despite the accompanying beta configuration.

Expected: Claude Opus 5 requests succeed, dropping stale thinking blocks when necessary.

Actual: the request is rejected due to the injected prefix_mismatch_behavior field.

Plugins

• oh-my-opencode-slim
• @datadog/opencode-plugin

OpenCode version

1.18.26

Steps to reproduce

1. Configure the amazon-bedrock provider in ap-southeast-1.
2. Use model amazon-bedrock/global.anthropic.claude-opus-5 with variant high.
3. Send a prompt through the primary agent.
4. Observe the request fail with the validation error above.

Screenshot and/or share link

No share link available. The exact error is included above.

Operating System

Ubuntu 24.04 on WSL2 (Linux 6.6.87.2-microsoft-standard-WSL2, x86_64)

Terminal

tmux (TERM=tmux-256color)