Reasoning Doesn't Work for Claude Models through Vertex Provider

[MichaelYochpaz]

Description

Hey, I'm using Claude Opus 4.5 through GCP Vertex AI, and noticed that for some reason, the reasoning doesn't work for me, even when reasoning is set to "high".

I initially thought it was perhaps hidden (I'm new to using OpenCode), but the responses I'm getting are way too fast for that, and I've tried toggling /thinking on and off, but it made no difference.

I also tried using a custom configuration on the config:

    "provider": {
        "google-vertex-anthropic": {
            "models": {
                "claude-opus-4-5@20251101": {
                    "variants": {
                        "test": {
                            "max_tokens": 64000,
                            "thinking": {
                                "type": "enabled",
                                "budget_tokens": 32000
                            }
                        }
                    }
                },
            },
        },
    },

But even using this "test" mode (which was successfully added) didn't change anything.
I also tested Claude Sonnet 4.5 and Opus 4 to check if it's specific to Opus 4.5, but those had the same issue.

I'll add that I used the same Vertex project with Roo Code and it used reasoning without any issues, so this shouldn't be an issue / limitation on my side.

I know this is not a lot of information to work with. If you need any additional information to help you debug this - please let me know how I can help.

Plugins

None

OpenCode version

v1.1.28

Steps to reproduce

No response

Screenshot and/or share link

https://opncd.ai/share/ha0A4Lmq

Operating System

macOS / Windows 11 (2 different devices, same issue)

Terminal

Windows Terminal / iTerm / OpenCode Desktop

[github-actions]

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

• No reasoning at all through Github Copilot provider #6864: No reasoning at all through Github Copilot provider (similar reasoning not being retrieved even with proper config)
• No Chain of Thought retrieved if Provider lacks support, despite thinkmode config #6768: No Chain of Thought retrieved if Provider lacks support, despite 'thinkmode' config (reasoning config being ignored by provider)
• [BUG/FEATURE]: Desktop GUI - Thinking process disappears and cannot be viewed in detail #8789: Desktop GUI - Thinking process disappears and cannot be viewed in detail (thinking content not persisting)
• Incorrect model IDs for Vertex Anthropic #9565: Incorrect model IDs for Vertex Anthropic (Vertex Anthropic provider configuration issues)
• Bug: Shared state between google-vertex and google-vertex-anthropic providers causes auth conflict #7514: Bug: Shared state between google-vertex and google-vertex-anthropic providers (Vertex AI provider conflicts)

Feel free to ignore if none of these address your specific case.

[rekram1-node]

this should be fairly straight forward to fix, i hope will look

[koverholt]

Thanks for the issue and the fix! I tried with OpenCode v1.1.34 and I'm still not seeing thinking with Claude Opus 4.5 via Vertex Anthropic (with /thinking enabled and variant set to high).

I think the npm string in #9953 should be @ai-sdk/google-vertex instead of @ai-sdk/google-vertex/anthropic based on the models.dev data?

$ jq '."google-vertex-anthropic" | {id, npm, name}' ~/.cache/opencode/models.json

{
  "id": "google-vertex-anthropic",
  "npm": "@ai-sdk/google-vertex",
  "name": "Vertex (Anthropic)"
}

[MichaelYochpaz]

@rekram1-node I also just tested v1.1.34 and reasoning is still not working.
cc @zerone0x

[MichaelYochpaz]

Opened #10442.
Tested locally and I can see thinking properly using Opus on Vertex following these changes :)