OpenCode: detect OpenAI-compatible Anthropic proxies (#25984, #26460)

Target

packages/opencode/src/provider/transform.ts → applyCaching() in sst/opencode.

Open issues: #25984 (Bifrost/LiteLLM → Bedrock), #26460 (Xiaomi MiMo).

Symptom

When the user routes Anthropic-shaped models through an OpenAI-compatible proxy (LiteLLM, Bifrost, or any @ai-sdk/openai-compatible adapter), OpenCode falls through to the OpenAI caching path and sets promptCacheKey (OpenAI shape). The proxy forwards this verbatim to the Anthropic backend, which ignores it. Result: 0% cache hit rate on what is otherwise the canonical "long agent loop on Claude" use case.

Affected routes:

• LiteLLM proxy → Bedrock Anthropic
• Bifrost → Bedrock Anthropic
• Xiaomi MiMo (Anthropic-shaped, marketed as OpenAI-compatible)
• Any custom @ai-sdk/openai-compatible endpoint with Claude backend

Fix

Broaden the detection predicate so OpenAI-compatible adapters with Anthropic-shaped models get Anthropic-style caching:

--- a/packages/opencode/src/provider/transform.ts
+++ b/packages/opencode/src/provider/transform.ts
@@ function applyCaching(msgs, model)
   if (
     model.providerID === "anthropic" ||
     model.api.id.includes("anthropic") ||
     model.api.id.includes("claude") ||
-    model.api.npm === "@ai-sdk/anthropic"
+    model.api.npm === "@ai-sdk/anthropic" ||
+    model.api.npm === "@ai-sdk/google-vertex/anthropic" ||
+    // OpenAI-compatible proxies routing to Anthropic-shaped backends
+    (model.api.npm === "@ai-sdk/openai-compatible" &&
+     (model.api.id.toLowerCase().includes("claude") ||
+      model.api.id.toLowerCase().includes("anthropic") ||
+      model.api.id.toLowerCase().includes("mimo"))) ||
+    // MiniMax and other Anthropic-shaped non-Anthropic models
+    model.api.id.startsWith("minimax/")
   ) {
     // Apply Anthropic-style cache_control on message blocks
   }

Optionally factor the predicate into a named helper (isAnthropicShapedRoute(model)) so the same check can be reused elsewhere in OpenCode.

Verify

1. Configure OpenCode with a LiteLLM endpoint pointing at a Bedrock Claude model:

   provider:
     openai-compatible:
       baseURL: http://localhost:4000/v1
       models:
         - claude-3-5-sonnet-bedrock
   

2. Run two identical prompts.
3. Capture wire to the LiteLLM endpoint.
4. Before fix: request body contains prompt_cache_key, no cache_control markers; response cache_read_input_tokens always 0.
5. After fix: request body has cache_control on system + last stable message; response shows cache_read_input_tokens > 0 on turn 2.

Background

This is a routing-layer detection bug, not a caching-logic bug. The caching CODE is fine; it just never runs for these models because the predicate didn't anticipate proxy-shaped routes.

Related skills:

• opencode-bedrock-doc-blocks (#17300) for the DocumentBlock case
• opencode-mistral-cache-key (#27556) for Mistral support

Full audit: audits/opencode.md.