diff --git a/open-sse/providers/capabilities.js b/open-sse/providers/capabilities.js
index c02f255f..b55244fb 100644
--- a/open-sse/providers/capabilities.js
+++ b/open-sse/providers/capabilities.js
@@ -165,6 +165,12 @@ export const PROVIDER_CAPABILITIES = {
     "deepseek-ai/deepseek-v4-pro": { reasoning: true, thinkingFormat: "openai", contextWindow: 1000000, maxOutput: 65536 },
     "deepseek-ai/deepseek-v4-flash": { reasoning: true, thinkingFormat: "openai", contextWindow: 1000000, maxOutput: 65536 },
   },
+  // glm-5.3-flash on OpenCode Go is served by a backend that rejects the z.ai
+  // `thinking` object (400: unknown field "thinking") and wants reasoning_effort.
+  // Overrides the global entry, whose z.ai shape is correct for z.ai itself.
+  "opencode-go": {
+    "glm-5.3-flash": { vision: true, videoInput: true, pdf: true, reasoning: true, thinkingFormat: "openai", thinkingCanDisable: false, contextWindow: 1000000, maxOutput: 131072 },
+  },
   "codex": {
     "gpt-6-astra":               { vision: true, reasoning: true, search: true, thinkingFormat: "openai", contextWindow: 272000, maxOutput: 128000 },
     "gpt-5.6-sol":               CODEX_GPT_56_SOL_CAPS,