diff --git a/open-sse/providers/thinkingLevels.js b/open-sse/providers/thinkingLevels.js
index 0890e4ec..89865593 100644
--- a/open-sse/providers/thinkingLevels.js
+++ b/open-sse/providers/thinkingLevels.js
@@ -42,6 +42,8 @@ const PATTERN_THINKING = [
   { provider: "codex", pattern: "*gpt-5.6-luna*", levels: CODEX_GPT_5_6_LEVELS },
   { pattern: "*codex*", levels: ["low", "medium", "high", "xhigh"] }, // codex cannot disable thinking
   { pattern: "*mimo*v2.6*", levels: ["none", "low", "medium", "high", "xhigh"] },
+  // mimo-v2.5-pro on opencode-go rejects reasoning_effort "max" (probed live); v2.5 accepts it.
+  { pattern: "*mimo*v2.5-pro*", levels: ["none", "low", "medium", "high", "xhigh"] },
   // DeepSeek v4.* (Alibaba MaaS, probed live): effort low|medium|high|xhigh|max
   // all 200 via output_config.effort; "none" is a 400 on the anthropic route
   // (disable thinking instead). none kept for the picker = disable.
diff --git a/open-sse/translator/concerns/thinkingUnified.js b/open-sse/translator/concerns/thinkingUnified.js
index 4bc9601f..3ccd442f 100644
--- a/open-sse/translator/concerns/thinkingUnified.js
+++ b/open-sse/translator/concerns/thinkingUnified.js
@@ -302,9 +302,12 @@ function applyFormat(fmt, body, cfg, caps, supportedLevels, display) {
     case "deepseek": {
       if (none && canDisable) { body.thinking = { type: "disabled" }; break; }
       body.thinking = { type: "enabled" };
-      // DeepSeek: low/medium→high, xhigh/max→max.
+      // DeepSeek: low/medium→high, xhigh/max→max. Some backends (mimo v2.5-pro/v2.6
+      // on opencode-go, probed live) 400 on "max" — clamp to high when the declared
+      // levels exclude it.
       const level = toLevel(eff);
-      body.reasoning_effort = level === "xhigh" || level === "max" ? "max" : "high";
+      const want = level === "xhigh" || level === "max" ? "max" : "high";
+      body.reasoning_effort = want === "max" && supportedLevels && !supportedLevels.includes("max") ? "high" : want;
       break;
     }
     case "kimi": {