Description
When switching from a model with extended thinking (e.g., Claude Opus with thinking enabled) to a model without thinking support (e.g., GPT 5.2, Claude Sonnet without thinking) mid-session, an error occurs:
messages.1.content.0.thinking: each thinking block must contain thinking
Root Cause
The reasoning parts from the previous model's responses are stored in the message history. When switching to a model that doesn't support interleaved reasoning (capabilities.interleaved === false), these parts are still sent to the API, causing validation errors.
Steps to Reproduce
- Start a conversation with Claude Opus (or any model with extended thinking)
- Get a response that includes thinking/reasoning blocks
- Switch to GPT 5.2 or Claude Sonnet (without thinking enabled) mid-session using Ctrl+M
- Send a new message
Expected Behavior
Switching models mid-session should work seamlessly. OpenCode should strip reasoning parts from message history when the target model doesn't support them.
Actual Behavior
API error about invalid thinking blocks.
Environment
- OpenCode version: 0.0.0-dev
- OS: macOS
- Provider: Anthropic / OpenAI
Related Issues
Description
When switching from a model with extended thinking (e.g., Claude Opus with thinking enabled) to a model without thinking support (e.g., GPT 5.2, Claude Sonnet without thinking) mid-session, an error occurs:
Root Cause
The
reasoningparts from the previous model's responses are stored in the message history. When switching to a model that doesn't support interleaved reasoning (capabilities.interleaved === false), these parts are still sent to the API, causing validation errors.Steps to Reproduce
Expected Behavior
Switching models mid-session should work seamlessly. OpenCode should strip reasoning parts from message history when the target model doesn't support them.
Actual Behavior
API error about invalid thinking blocks.
Environment
Related Issues
signatureinthinkingblock when switching Claude models (Copilot provider) #11546 (similar but for Claude-to-Claude switching with signature issues)