diff --git a/open-sse/config/providerModels.js b/open-sse/config/providerModels.js
index afa98fa7..f4747cd4 100644
--- a/open-sse/config/providerModels.js
+++ b/open-sse/config/providerModels.js
@@ -53,7 +53,7 @@ export function findModelName(aliasOrId, modelId) {
 }
 
 export function getModelTargetFormat(aliasOrId, modelId) {
-  if ((!aliasOrId || aliasOrId === "oc" || aliasOrId === "opencode" || aliasOrId === "ocg" || aliasOrId === "opencode-go") && isMuseSparkModel(modelId)) {
+  if ((!aliasOrId || aliasOrId === "oc" || aliasOrId === "opencode" || aliasOrId === "ocg" || aliasOrId === "opencode-go" || aliasOrId === "ocz" || aliasOrId === "opencode-zen") && isMuseSparkModel(modelId)) {
     return FORMATS.OPENAI_RESPONSES;
   }
   const models = PROVIDER_MODELS[aliasOrId];
diff --git a/open-sse/executors/index.js b/open-sse/executors/index.js
index f48a8ecb..ed17d330 100644
--- a/open-sse/executors/index.js
+++ b/open-sse/executors/index.js
@@ -11,6 +11,7 @@ import { CursorExecutor } from "./cursor.js";
 import { VertexExecutor } from "./vertex.js";
 import { OpenCodeExecutor } from "./opencode.js";
 import { OpenCodeGoExecutor } from "./opencode-go.js";
+import { OpenCodeZenExecutor } from "./opencode-zen.js";
 import { GrokWebExecutor } from "./grok-web.js";
 import { GrokCliExecutor } from "./grok-cli.js";
 import { PerplexityWebExecutor } from "./perplexity-web.js";
@@ -43,6 +44,7 @@ const executors = {
   "vertex-partner": new VertexExecutor("vertex-partner"),
   opencode: new OpenCodeExecutor(),
   "opencode-go": new OpenCodeGoExecutor(),
+  "opencode-zen": new OpenCodeZenExecutor(),
   "grok-web": new GrokWebExecutor(),
   "grok-cli": new GrokCliExecutor(),
   gcli: new GrokCliExecutor(), // Alias
@@ -89,6 +91,7 @@ export { VertexExecutor } from "./vertex.js";
 export { DefaultExecutor } from "./default.js";
 export { OpenCodeExecutor } from "./opencode.js";
 export { OpenCodeGoExecutor } from "./opencode-go.js";
+export { OpenCodeZenExecutor } from "./opencode-zen.js";
 export { GrokWebExecutor } from "./grok-web.js";
 export { GrokCliExecutor } from "./grok-cli.js";
 export { PerplexityWebExecutor } from "./perplexity-web.js";
diff --git a/open-sse/executors/opencode-zen.js b/open-sse/executors/opencode-zen.js
new file mode 100644
index 00000000..8a43ff85
--- /dev/null
+++ b/open-sse/executors/opencode-zen.js
@@ -0,0 +1,315 @@
+import crypto from "node:crypto";
+import { DefaultExecutor } from "./default.js";
+import { resolveSessionId } from "../utils/sessionManager.js";
+import { isMuseSparkModel } from "../providers/models/helpers.js";
+import {
+  normalizeResponsesInput,
+  clampResponsesCallId,
+  coerceResponsesArguments,
+  coerceResponsesOutput,
+} from "../translator/formats/responsesApi.js";
+
+const SESSION_HEADER = "x-opencode-session";
+const SESSION_FIELD = "_opencodeZenSession";
+const MAX_SESSION_LENGTH = 256;
+
+const RESPONSES_BASE_URL = "https://opencode.ai/zen/v1/responses";
+const MAX_TOOL_NAME_LEN = 128;
+const OPENCODE_UA = "opencode/1.18.31";
+export const OPENCODE_SESSION_RE = /^ses_[0-9a-f]{12}[0-9A-Za-z]{14}$/;
+const BASE62_CHARS = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz";
+// Free-tier fingerprint (mirrors opencode executor, PR #4132): upstream 403s
+// requests without the file-search quartet and without stream:true.
+const OPENCODE_FINGERPRINT_TOOLS = ["bash", "glob", "grep", "read"];
+
+function hasValidOpencodeVersion(ua) {
+  const m = String(ua || "").match(/opencode\/(\d+)\.(\d+)(?:\.(\d+))?/i);
+  if (!m) return false;
+  const major = parseInt(m[1], 10);
+  const minor = parseInt(m[2], 10);
+  return major > 1 || (major === 1 && minor >= 17);
+}
+
+function unstableRandom() {
+  const bytes = crypto.randomBytes(14);
+  let randomPart = "";
+  for (let i = 0; i < 14; i++) {
+    randomPart += BASE62_CHARS[bytes[i] % 62];
+  }
+  return randomPart;
+}
+
+export function generateSessionId(timestamp = Date.now()) {
+  const current = BigInt(timestamp) * 0x1000n + 1n;
+  const value = ~current;
+  const time = Array.from({ length: 6 }, (_, index) =>
+    Number((value >> BigInt(40 - 8 * index)) & 0xffn)
+      .toString(16)
+      .padStart(2, "0")
+  ).join("");
+  return `ses_${time}${unstableRandom()}`;
+}
+
+export function generateRequestId(timestamp = Date.now()) {
+  const current = BigInt(timestamp) * 0x1000n + 1n;
+  const value = current;
+  const time = Array.from({ length: 6 }, (_, index) =>
+    Number((value >> BigInt(40 - 8 * index)) & 0xffn)
+      .toString(16)
+      .padStart(2, "0")
+  ).join("");
+  return `msg_${time}${unstableRandom()}`;
+}
+
+export function translateSessionId(sessionId, clientTool = "") {
+  if (typeof sessionId === "string" && OPENCODE_SESSION_RE.test(sessionId.trim())) {
+    return sessionId.trim();
+  }
+  const digest = crypto
+    .createHash("sha256")
+    .update(`opencode\0${clientTool || "generic"}\0${sessionId || ""}`)
+    .digest();
+  const timeHex = digest.subarray(0, 6).toString("hex");
+  let randomPart = "";
+  for (let i = 6; i < 20; i++) {
+    randomPart += BASE62_CHARS[digest[i] % 62];
+  }
+  return `ses_${timeHex}${randomPart}`;
+}
+
+function toolNameOf(tool) {
+  if (!tool || typeof tool !== "object" || Array.isArray(tool)) return "";
+  const fn = tool.function && typeof tool.function === "object" && !Array.isArray(tool.function) ? tool.function : null;
+  const raw = typeof tool.name === "string" ? tool.name : (typeof fn?.name === "string" ? fn.name : "");
+  return raw.trim();
+}
+
+function ensureChatFingerprintTools(body) {
+  if (!body || typeof body !== "object") return;
+  const present = new Set();
+  if (Array.isArray(body.tools)) {
+    for (const tool of body.tools) {
+      const name = toolNameOf(tool);
+      if (name) present.add(name);
+    }
+  } else {
+    body.tools = [];
+  }
+  for (const name of OPENCODE_FINGERPRINT_TOOLS) {
+    if (present.has(name)) continue;
+    body.tools.push({
+      type: "function",
+      function: {
+        name,
+        description: `OpenCode built-in ${name} tool`,
+        parameters: { type: "object", properties: {} },
+      },
+    });
+    present.add(name);
+  }
+}
+
+function ensureResponsesFingerprintTools(body) {
+  if (!body || typeof body !== "object") return;
+  const present = new Set();
+  if (Array.isArray(body.tools)) {
+    for (const tool of body.tools) {
+      const name = toolNameOf(tool);
+      if (name) present.add(name);
+    }
+  } else {
+    body.tools = [];
+  }
+  for (const name of OPENCODE_FINGERPRINT_TOOLS) {
+    if (present.has(name)) continue;
+    body.tools.push({
+      type: "function",
+      name,
+      description: `OpenCode built-in ${name} tool`,
+      parameters: { type: "object", properties: {} },
+    });
+    present.add(name);
+  }
+}
+
+function normalizeSession(value) {
+  if (typeof value !== "string") return null;
+  const normalized = value.trim();
+  if (!normalized || normalized.length > MAX_SESSION_LENGTH) return null;
+  return normalized;
+}
+
+function nativeSession(headers) {
+  if (!headers || typeof headers !== "object") return null;
+  for (const [key, value] of Object.entries(headers)) {
+    if (key.toLowerCase() === SESSION_HEADER) {
+      const normalized = normalizeSession(value);
+      if (normalized && OPENCODE_SESSION_RE.test(normalized)) return normalized;
+    }
+  }
+  return null;
+}
+
+function translatedSession(sessionId, clientTool) {
+  return translateSessionId(sessionId, clientTool);
+}
+
+// Strip the thinking suffix "model(level)" so checks hit the base id.
+function baseModelId(model) {
+  return String(model || "").replace(/\([^()]+\)\s*$/, "").trim();
+}
+
+function isResponsesModel(model) {
+  return isMuseSparkModel(baseModelId(model));
+}
+
+// Flatten Chat Completions tool declarations into the Responses flat shape and
+// drop hosted/nameless tools the /responses endpoint rejects.
+function normalizeResponsesTools(body) {
+  if (!Array.isArray(body.tools)) return;
+  const validNames = new Set();
+  body.tools = body.tools.filter((tool) => {
+    if (!tool || typeof tool !== "object" || Array.isArray(tool)) return false;
+    const fn = tool.function && typeof tool.function === "object" && !Array.isArray(tool.function) ? tool.function : null;
+    const rawName = typeof tool.name === "string" ? tool.name : (typeof fn?.name === "string" ? fn.name : "");
+    const name = rawName.trim();
+    if (!name) return false;
+    const description = typeof tool.description === "string" ? tool.description : (typeof fn?.description === "string" ? fn.description : "");
+    let parameters = (tool.parameters && typeof tool.parameters === "object" && !Array.isArray(tool.parameters))
+      ? tool.parameters
+      : (fn?.parameters && typeof fn.parameters === "object" && !Array.isArray(fn.parameters) ? fn.parameters : { type: "object", properties: {} });
+    // Mirror the request translator: {type:"object"} without properties is rejected
+    // by strict Responses backends, so fill in the empty properties map.
+    if (parameters.type === "object" && !parameters.properties) parameters = { ...parameters, properties: {} };
+    for (const k of Object.keys(tool)) delete tool[k];
+    tool.type = "function";
+    tool.name = name.slice(0, MAX_TOOL_NAME_LEN);
+    if (description) tool.description = description;
+    tool.parameters = parameters;
+    validNames.add(tool.name);
+    return true;
+  });
+  if (body.tool_choice && typeof body.tool_choice === "object" && !Array.isArray(body.tool_choice)) {
+    if (body.tool_choice.type === "function") {
+      const n = typeof body.tool_choice.name === "string" ? body.tool_choice.name.trim() : "";
+      if (!n || !validNames.has(n)) delete body.tool_choice;
+    }
+  }
+}
+
+// Last line of defense for native Responses clients (sourceFormat === targetFormat
+// skips translation): coerce items in place so malformed tool payloads 400 here
+// with a clear shape instead of upstream as InputValidationError.
+function sanitizeResponsesItems(body) {
+  if (!Array.isArray(body.input)) return;
+  body.input = body.input.filter((item) => {
+    if (!item || typeof item !== "object" || Array.isArray(item)) return true;
+    // Strip prior-turn reasoning items: Muse Spark contributor models route to
+    // an upstream Console backend where encrypted_content cannot be validated across
+    // rotated accounts or sessions, causing 400 "reasoning encrypted_content was not issued to this caller".
+    if (item.type === "reasoning") return false;
+    delete item.encrypted_content;
+    delete item.reasoning_encrypted_content;
+    if (item.type === "function_call") {
+      if (!item.name || typeof item.name !== "string" || item.name.trim() === "") return false;
+      item.name = item.name.trim().slice(0, MAX_TOOL_NAME_LEN);
+      item.call_id = clampResponsesCallId(item.call_id);
+      item.arguments = coerceResponsesArguments(item.arguments);
+      return true;
+    }
+    if (item.type === "function_call_output") {
+      item.call_id = clampResponsesCallId(item.call_id);
+      item.output = coerceResponsesOutput(item.output);
+      return true;
+    }
+    return true;
+  });
+}
+
+export class OpenCodeZenExecutor extends DefaultExecutor {
+  constructor() {
+    super("opencode-zen");
+  }
+
+  buildUrl(model, stream, urlIndex = 0, credentials = null) {
+    // Muse Spark lives on /responses even when a stale runtimeTransport leaks in.
+    if (isResponsesModel(model)) return RESPONSES_BASE_URL;
+    return super.buildUrl(model, stream, urlIndex, credentials);
+  }
+
+  prepareRequestCredentials({ body, credentials, providerSessionId, clientTool } = {}) {
+    const sourceCredentials = credentials || {};
+    const native = nativeSession(sourceCredentials.rawHeaders);
+    const resolved = normalizeSession(providerSessionId) || resolveSessionId({
+      headers: sourceCredentials.rawHeaders,
+      body,
+      connectionId: sourceCredentials.connectionId,
+      scope: "opencode-zen",
+    });
+
+    return {
+      ...sourceCredentials,
+      [SESSION_FIELD]: native || translatedSession(resolved, clientTool),
+    };
+  }
+
+  async execute(args) {
+    const credentials = this.prepareRequestCredentials(args);
+    return super.execute({ ...args, credentials });
+  }
+
+  buildHeaders(credentials, stream = true, url, model) {
+    const headers = super.buildHeaders(credentials || {}, stream, url, model);
+    const raw = credentials?.rawHeaders || {};
+    const lower = {};
+    for (const [k, v] of Object.entries(raw)) lower[k.toLowerCase()] = v;
+    const downstreamUa = lower["user-agent"] || "";
+    // Free-tier gate: spoof the official client UA.
+    headers["User-Agent"] = hasValidOpencodeVersion(downstreamUa) ? downstreamUa : OPENCODE_UA;
+    headers["x-opencode-client"] = lower["x-opencode-client"] || "desktop";
+    const prepared = credentials?.[SESSION_FIELD];
+    if (prepared) {
+      headers[SESSION_HEADER] = prepared;
+      return headers;
+    }
+
+    const fallback = this.prepareRequestCredentials({ credentials });
+    headers[SESSION_HEADER] = fallback[SESSION_FIELD];
+    return headers;
+  }
+
+  transformRequest(model, body, stream, credentials) {
+    const out = super.transformRequest(model, body);
+    // Free-tier gate: upstream 403s stream:false even when everything else is valid.
+    if (out && typeof out === "object") out.stream = true;
+    if (!isResponsesModel(model || body?.model)) {
+      ensureChatFingerprintTools(out);
+      return out;
+    }
+    const normalized = normalizeResponsesInput(out.input);
+    if (normalized) out.input = normalized;
+    if (!Array.isArray(out.input) || out.input.length === 0) {
+      out.input = [{ type: "message", role: "user", content: [{ type: "input_text", text: "..." }] }];
+    }
+    // Responses names the output cap max_output_tokens, not max_tokens.
+    if (out.max_output_tokens === undefined) {
+      if (out.max_completion_tokens !== undefined) out.max_output_tokens = out.max_completion_tokens;
+      else if (out.max_tokens !== undefined) out.max_output_tokens = out.max_tokens;
+    }
+    delete out.max_tokens;
+    delete out.max_completion_tokens;
+    if (out.reasoning_effort !== undefined && out.reasoning === undefined) {
+      out.reasoning = { effort: out.reasoning_effort, summary: "auto" };
+    }
+    if (out.reasoning && typeof out.reasoning === "object" && !Array.isArray(out.reasoning)) {
+      if (!out.reasoning.summary) out.reasoning.summary = "auto";
+    }
+    delete out.reasoning_effort;
+    out.stream = true;
+    out.store = false;
+    ensureResponsesFingerprintTools(out);
+    normalizeResponsesTools(out);
+    sanitizeResponsesItems(out);
+    return out;
+  }
+}
diff --git a/open-sse/providers/registry/index.js b/open-sse/providers/registry/index.js
index fb355d6d..56a8d41d 100644
--- a/open-sse/providers/registry/index.js
+++ b/open-sse/providers/registry/index.js
@@ -69,6 +69,7 @@ import p66 from "./ollama.js";
 import p123 from "./ollama-search.js";
 import p67 from "./openai.js";
 import p68 from "./opencode-go.js";
+import p68z from "./opencode-zen.js";
 import p69 from "./opencode.js";
 import p70 from "./openrouter.js";
 import p71 from "./perplexity-web.js";
@@ -194,6 +195,7 @@ export default [
   p123,
   p67,
   p68,
+  p68z,
   p69,
   p70,
   p71,
diff --git a/open-sse/providers/registry/opencode-zen.js b/open-sse/providers/registry/opencode-zen.js
new file mode 100644
index 00000000..8ec2ff1f
--- /dev/null
+++ b/open-sse/providers/registry/opencode-zen.js
@@ -0,0 +1,123 @@
+export default {
+  id: "opencode-zen",
+  priority: 205,
+  alias: "ocz",
+  aliases: [
+    "opencode-zen",
+  ],
+  uiAlias: "ocz",
+  display: {
+    name: "OpenCode Zen",
+    icon: "terminal",
+    color: "#E87040",
+    textIcon: "OZ",
+    website: "https://opencode.ai/auth",
+    notice: {
+      text: "OpenCode Zen PAYG: pay-as-you-go, key from https://opencode.ai/auth. Same models as Zen: paid + free tiers on the fast lane.",
+      apiKeyUrl: "https://opencode.ai/auth",
+    },
+  },
+  category: "apikey",
+  transport: {
+    baseUrl: "https://opencode.ai/zen/v1/chat/completions",
+    headers: {},
+    usage: {
+      url: "https://opencode.ai/zen/v1/usage",
+    },
+  },
+  // Multi-endpoint: pick the transport matching the client sourceFormat to skip
+  // translation. Mirrors opencode-go, pointed at /zen/v1 (see https://opencode.ai/docs/zen/).
+  transports: [
+    { format: "openai", baseUrl: "https://opencode.ai/zen/v1/chat/completions", auth: { combined: true, header: "Authorization", scheme: "bearer" } },
+    { format: "claude", baseUrl: "https://opencode.ai/zen/v1/messages", auth: { combined: true, header: "x-api-key", scheme: "raw", anthropicVersion: true } },
+    { format: "openai-responses", baseUrl: "https://opencode.ai/zen/v1/responses", auth: { combined: true, header: "Authorization", scheme: "bearer" } },
+  ],
+  // supportedFormats follow the endpoint table in https://opencode.ai/docs/zen/
+  // (live /zen/v1/models, 2026-09-18: 71 ids).
+  models: [
+    // Claude (messages)
+    { id: "claude-fable-5", name: "Claude Fable 5", supportedFormats: ["claude"] },
+    { id: "claude-fable-5-1", name: "Claude Fable 5.1", supportedFormats: ["claude"] },
+    { id: "claude-opus-5", name: "Claude Opus 5", supportedFormats: ["claude"] },
+    { id: "claude-opus-4-8", name: "Claude Opus 4.8", supportedFormats: ["claude"] },
+    { id: "claude-opus-4-7", name: "Claude Opus 4.7", supportedFormats: ["claude"] },
+    { id: "claude-opus-4-6", name: "Claude Opus 4.6", supportedFormats: ["claude"] },
+    { id: "claude-opus-4-5", name: "Claude Opus 4.5", supportedFormats: ["claude"] },
+    { id: "claude-sonnet-5", name: "Claude Sonnet 5", supportedFormats: ["claude"] },
+    { id: "claude-sonnet-4-6", name: "Claude Sonnet 4.6", supportedFormats: ["claude"] },
+    { id: "claude-sonnet-4-5", name: "Claude Sonnet 4.5", supportedFormats: ["claude"] },
+    { id: "claude-sonnet-4", name: "Claude Sonnet 4", supportedFormats: ["claude"] },
+    { id: "claude-haiku-4-5", name: "Claude Haiku 4.5", supportedFormats: ["claude"] },
+    // Gemini (own path, via chat completions transport)
+    { id: "gemini-3.6-flash", name: "Gemini 3.6 Flash", supportedFormats: ["openai"] },
+    { id: "gemini-3.8-flash", name: "Gemini 3.8 Flash", supportedFormats: ["openai"] },
+    { id: "gemini-3.7-flash", name: "Gemini 3.7 Flash", supportedFormats: ["openai"] },
+    { id: "gemini-3.5-flash-lite", name: "Gemini 3.5 Flash Lite", supportedFormats: ["openai"] },
+    { id: "gemini-3.5-flash", name: "Gemini 3.5 Flash", supportedFormats: ["openai"] },
+    { id: "gemini-3.1-pro", name: "Gemini 3.1 Pro", supportedFormats: ["openai"] },
+    { id: "gemini-3-flash", name: "Gemini 3 Flash", supportedFormats: ["openai"] },
+    // GPT / Grok / Muse Spark paid (responses)
+    { id: "gpt-6-astra", name: "GPT 6 Astra", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.6-sol", name: "GPT 5.6 Sol", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.6-terra", name: "GPT 5.6 Terra", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.6-luna", name: "GPT 5.6 Luna", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.5", name: "GPT 5.5", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.5-pro", name: "GPT 5.5 Pro", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.4", name: "GPT 5.4", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.4-pro", name: "GPT 5.4 Pro", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.4-mini", name: "GPT 5.4 Mini", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.4-nano", name: "GPT 5.4 Nano", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.3-codex-spark", name: "GPT 5.3 Codex Spark", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.3-codex", name: "GPT 5.3 Codex", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.2", name: "GPT 5.2", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.2-codex", name: "GPT 5.2 Codex", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.1", name: "GPT 5.1", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.1-codex-max", name: "GPT 5.1 Codex Max", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.1-codex", name: "GPT 5.1 Codex", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5.1-codex-mini", name: "GPT 5.1 Codex Mini", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5", name: "GPT 5", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5-codex", name: "GPT 5 Codex", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "gpt-5-nano", name: "GPT 5 Nano", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "grok-build-0.1", name: "Grok Build 0.1", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "grok-4.6", name: "Grok 4.6", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "grok-4.5", name: "Grok 4.5", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "muse-spark-1.3", name: "Muse Spark 1.3", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "muse-spark-1.2", name: "Muse Spark 1.2", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    // Qwen paid (messages)
+    { id: "qwen3.6-plus", name: "Qwen 3.6 Plus", supportedFormats: ["claude"] },
+    { id: "qwen3.5-plus", name: "Qwen 3.5 Plus", supportedFormats: ["claude"] },
+    // DeepSeek / GLM / MiniMax / Kimi / Big Pickle (chat completions)
+    { id: "deepseek-v4-pro", name: "DeepSeek V4 Pro", supportedFormats: ["openai"] },
+    { id: "deepseek-v4-flash", name: "DeepSeek V4 Flash", supportedFormats: ["openai"] },
+    { id: "deepseek-v4-flash-vision-exp", name: "DeepSeek V4 Flash Vision Exp", supportedFormats: ["openai"] },
+    { id: "glm-5.3-flash", name: "GLM 5.3 Flash (Vision)", supportedFormats: ["openai"] },
+    { id: "glm-5.3", name: "GLM 5.3", supportedFormats: ["openai"] },
+    { id: "glm-5.2", name: "GLM 5.2", supportedFormats: ["openai"] },
+    { id: "glm-5.1", name: "GLM 5.1", supportedFormats: ["openai"] },
+    { id: "glm-5", name: "GLM 5", supportedFormats: ["openai"] },
+    { id: "minimax-m3", name: "MiniMax M3", supportedFormats: ["openai"] },
+    { id: "minimax-m2.7", name: "MiniMax M2.7", supportedFormats: ["openai"] },
+    { id: "minimax-m2.5", name: "MiniMax M2.5", supportedFormats: ["openai"] },
+    { id: "kimi-k3", name: "Kimi K3", supportedFormats: ["openai"] },
+    { id: "kimi-k2.7-code", name: "Kimi K2.7 Code", supportedFormats: ["openai"] },
+    { id: "kimi-k2.6", name: "Kimi K2.6", supportedFormats: ["openai"] },
+    { id: "kimi-k2.5", name: "Kimi K2.5", supportedFormats: ["openai"] },
+    { id: "big-pickle", name: "Big Pickle", supportedFormats: ["openai"] },
+    { id: "union-alpha", name: "Union Alpha", supportedFormats: ["claude"] },
+    // Free tier on the keyed lane (chat completions)
+    { id: "deepseek-v4-flash-free", name: "DeepSeek V4 Flash Free", supportedFormats: ["openai"] },
+    { id: "mimo-v2.5-free", name: "MiMo V2.5 Free", supportedFormats: ["openai"] },
+    { id: "ling-3.0-flash-fin-free", name: "Ling 3.0 Flash Fin Free", supportedFormats: ["openai"] },
+    { id: "nemotron-3-ultra-free", name: "Nemotron 3 Ultra Free", supportedFormats: ["openai"] },
+    { id: "nemotron-3.5-lightning-free", name: "Nemotron 3.5 Lightning Free", supportedFormats: ["openai"] },
+    // Free tier on the keyed lane (responses)
+    { id: "muse-spark-1.3-contributor-free", name: "Muse Spark 1.3 Contributor Free", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+    { id: "muse-spark-1.2-contributor-free", name: "Muse Spark 1.2 Contributor Free", targetFormat: "openai-responses", supportedFormats: ["openai-responses"] },
+  ],
+  modelsFetcher: { url: "https://opencode.ai/zen/v1/models", type: "opencode-free" },
+  passthroughModels: true,
+  features: {
+    usage: true,
+    usageApikey: true,
+  },
+};
diff --git a/open-sse/services/usage.js b/open-sse/services/usage.js
index cca5d861..90ecb0e9 100644
--- a/open-sse/services/usage.js
+++ b/open-sse/services/usage.js
@@ -15,6 +15,7 @@ import { getGrokCliUsage } from "./usage/grok-cli.js";
 import { getKimiUsage } from "./usage/kimi.js";
 import { getDeepseekUsage } from "./usage/deepseek.js";
 import { getOpenCodeGoUsage } from "./usage/opencode-go.js";
+import { getOpenCodeZenUsage } from "./usage/opencode-zen.js";
 import { getGroqUsage } from "./usage/groq.js";
 import { getZedUsage } from "./usage/zed.js";
 import { getXiaomiMimoUsage } from "./usage/xiaomi-mimo.js";
@@ -59,6 +60,7 @@ const USAGE_HANDLERS = {
   "grok-cli": (c) => getGrokCliUsage(c.accessToken, c.providerSpecificData, c.proxyOptions),
   kimi: (c) => getKimiUsage(c.accessToken, c.apiKey, c.proxyOptions, c.providerSpecificData),
   "opencode-go": (c) => getOpenCodeGoUsage(c.apiKey, c.proxyOptions),
+  "opencode-zen": (c) => getOpenCodeZenUsage(c.apiKey, c.proxyOptions),
   deepseek: (c) => getDeepseekUsage(c.apiKey, c.proxyOptions),
   groq: (c) => getGroqUsage(c.apiKey, c.proxyOptions),
   zed: (c) => getZedUsage(c.accessToken, c.providerSpecificData, c.proxyOptions),
diff --git a/open-sse/services/usage/opencode-zen.js b/open-sse/services/usage/opencode-zen.js
new file mode 100644
index 00000000..54dacec8
--- /dev/null
+++ b/open-sse/services/usage/opencode-zen.js
@@ -0,0 +1,107 @@
+/**
+ * OpenCode Zen usage — GET https://opencode.ai/zen/v1/usage
+ * Auth: Bearer <apiKey>
+ */
+
+import { proxyAwareFetch } from "../../utils/proxyFetch.js";
+import { parseResetTime, toFiniteNumber, U } from "./shared.js";
+
+const USAGE_URL = U("opencode-zen").url;
+const QUOTA_NAMES = {
+  rolling: "Rolling",
+  weekly: "Weekly",
+  monthly: "Monthly",
+};
+
+function parsePercent(value) {
+  if (typeof value === "number" && Number.isFinite(value)) return value;
+  if (typeof value === "string" && value.trim()) {
+    const parsed = Number(value);
+    if (Number.isFinite(parsed)) return parsed;
+  }
+  return null;
+}
+
+export async function getOpenCodeZenUsage(apiKey = null, proxyOptions = null) {
+  if (!apiKey || typeof apiKey !== "string" || !apiKey.trim()) {
+    return {
+      message: "OpenCode Zen API key not available. Add a key to view usage.",
+    };
+  }
+
+  try {
+    const response = await proxyAwareFetch(
+      USAGE_URL,
+      {
+        method: "GET",
+        headers: {
+          Authorization: `Bearer ${apiKey.trim()}`,
+          Accept: "application/json",
+        },
+      },
+      proxyOptions,
+    );
+
+    if (response.status === 401) {
+      return {
+        plan: "OpenCode Zen",
+        message: "OpenCode Zen authentication failed. Check the API key.",
+      };
+    }
+
+    if (response.status === 403) {
+      const error = await response.json().catch(() => null);
+      const subscriptionRequired = error?.error?.type === "EntitlementError";
+      return {
+        plan: "OpenCode Zen",
+        message: subscriptionRequired
+          ? "OpenCode Zen billing required for this API key."
+          : "OpenCode Zen access forbidden for this API key.",
+      };
+    }
+
+    if (!response.ok) {
+      return {
+        plan: "OpenCode Zen",
+        message: `OpenCode Zen usage API error (${response.status}).`,
+      };
+    }
+
+    const data = await response.json().catch(() => null);
+    if (!data?.usage || typeof data.usage !== "object") {
+      return {
+        plan: "OpenCode Zen",
+        message: "OpenCode Zen usage response did not contain quota data.",
+      };
+    }
+
+    const quotas = {};
+    for (const [period, name] of Object.entries(QUOTA_NAMES)) {
+      const quota = data.usage[period];
+      if (!quota || typeof quota !== "object") continue;
+      const percent = parsePercent(quota.percent);
+      if (percent === null) continue;
+      const used = Math.max(0, Math.min(100, toFiniteNumber(percent, 0)));
+      quotas[name] = {
+        used,
+        total: 100,
+        remaining: 100 - used,
+        remainingPercentage: 100 - used,
+        resetAt: parseResetTime(quota.resetsAt),
+        unlimited: false,
+      };
+    }
+
+
+    if (Object.keys(quotas).length === 0) {
+      return {
+        plan: "OpenCode Zen",
+        message: "OpenCode Zen usage response did not contain valid quota data.",
+      };
+    }
+
+    return { plan: "OpenCode Zen", quotas };
+  } catch (error) {
+    return { message: `OpenCode Zen error: ${error.message}` };
+  }
+}
diff --git a/tests/__baseline__/alias-baseline.json b/tests/__baseline__/alias-baseline.json
index ae3a452f..fee2d748 100644
--- a/tests/__baseline__/alias-baseline.json
+++ b/tests/__baseline__/alias-baseline.json
@@ -180,6 +180,7 @@
     "openai": "openai",
     "opencode": "oc",
     "opencode-go": "opencode-go",
+    "opencode-zen": "ocz",
     "openrouter": "openrouter",
     "perplexity": "perplexity",
     "perplexity-agent": "perplexity-agent",
@@ -265,6 +266,7 @@
     "nebius",
     "nvidia",
     "oc",
+    "ocz",
     "ollama",
     "openai",
     "openai-tts-models",
diff --git a/tests/__baseline__/providers-baseline.json b/tests/__baseline__/providers-baseline.json
index 89a3db64..d4de0970 100644
--- a/tests/__baseline__/providers-baseline.json
+++ b/tests/__baseline__/providers-baseline.json
@@ -762,6 +762,44 @@
       }
     ]
   },
+  "opencode-zen": {
+    "baseUrl": "https://opencode.ai/zen/v1/chat/completions",
+    "headers": {},
+    "usage": {
+      "url": "https://opencode.ai/zen/v1/usage"
+    },
+    "format": "openai",
+    "transports": [
+      {
+        "format": "openai",
+        "baseUrl": "https://opencode.ai/zen/v1/chat/completions",
+        "auth": {
+          "combined": true,
+          "header": "Authorization",
+          "scheme": "bearer"
+        }
+      },
+      {
+        "format": "claude",
+        "baseUrl": "https://opencode.ai/zen/v1/messages",
+        "auth": {
+          "combined": true,
+          "header": "x-api-key",
+          "scheme": "raw",
+          "anthropicVersion": true
+        }
+      },
+      {
+        "format": "openai-responses",
+        "baseUrl": "https://opencode.ai/zen/v1/responses",
+        "auth": {
+          "combined": true,
+          "header": "Authorization",
+          "scheme": "bearer"
+        }
+      }
+    ]
+  },
   "opencode": {
     "baseUrl": "https://opencode.ai",
     "headers": {
diff --git a/tests/unit/opencode-zen-models.test.js b/tests/unit/opencode-zen-models.test.js
new file mode 100644
index 00000000..3812d400
--- /dev/null
+++ b/tests/unit/opencode-zen-models.test.js
@@ -0,0 +1,123 @@
+import { describe, expect, it } from "vitest";
+import { PROVIDER_MODELS, getModelSupportedFormats } from "../../open-sse/config/providerModels.js";
+import { PROVIDERS } from "../../open-sse/config/providers.js";
+import { resolveTransport } from "../../open-sse/services/provider.js";
+
+// Chat-only models (no /messages, no /responses support on opencode-zen)
+const CHAT_ONLY = ["deepseek-v4-pro", "deepseek-v4-flash", "deepseek-v4-flash-vision-exp",
+  "glm-5.3-flash", "glm-5.3", "glm-5.2", "glm-5.1", "glm-5",
+  "minimax-m3", "minimax-m2.7", "minimax-m2.5",
+  "kimi-k3", "kimi-k2.7-code", "kimi-k2.6", "kimi-k2.5",
+  "big-pickle", "deepseek-v4-flash-free",
+  "mimo-v2.5-free", "ling-3.0-flash-fin-free", "nemotron-3-ultra-free", "nemotron-3.5-lightning-free"];
+// Models that also expose the Anthropic /messages endpoint
+const CLAUDE_CAPABLE = ["claude-fable-5", "claude-fable-5-1", "claude-opus-5",
+  "claude-opus-4-8", "claude-opus-4-7", "claude-opus-4-6", "claude-opus-4-5",
+  "claude-sonnet-5", "claude-sonnet-4-6", "claude-sonnet-4-5", "claude-sonnet-4",
+  "claude-haiku-4-5", "qwen3.6-plus", "qwen3.5-plus", "union-alpha"];
+// Models that also expose the OpenAI /responses endpoint
+const RESPONSES_CAPABLE = ["gpt-6-astra",
+  "gpt-5.6-sol", "gpt-5.6-terra", "gpt-5.6-luna",
+  "gpt-5.5", "gpt-5.5-pro",
+  "gpt-5.4", "gpt-5.4-pro", "gpt-5.4-mini", "gpt-5.4-nano",
+  "gpt-5.3-codex-spark", "gpt-5.3-codex",
+  "gpt-5.2", "gpt-5.2-codex",
+  "gpt-5.1", "gpt-5.1-codex-max", "gpt-5.1-codex", "gpt-5.1-codex-mini",
+  "gpt-5", "gpt-5-codex", "gpt-5-nano",
+  "grok-build-0.1", "grok-4.6", "grok-4.5",
+  "muse-spark-1.3", "muse-spark-1.2",
+  "muse-spark-1.3-contributor-free", "muse-spark-1.2-contributor-free"];
+
+// Mirror of chatCore's per-model transport guard: use the sourceFormat-matched
+// transport only when the model declares support for that sourceFormat.
+function pickTransport(provider, sourceFormat, alias, model) {
+  const supported = getModelSupportedFormats(alias, model);
+  const rt = resolveTransport(provider, sourceFormat);
+  return supported?.includes(sourceFormat) ? rt : null;
+}
+
+describe("OpenCode Zen model catalog", () => {
+  it("matches the documented model IDs", () => {
+    const ids = (PROVIDER_MODELS["ocz"] || []).map((m) => m.id);
+    expect(ids).toContain("muse-spark-1.3-contributor-free");
+    expect(ids).toContain("gpt-5.5");
+    expect(ids).toContain("claude-opus-5");
+    expect(ids).toContain("kimi-k3");
+    expect(ids).toContain("deepseek-v4-pro");
+    expect(ids.length).toBeGreaterThan(60);
+  });
+});
+
+describe("OpenCode Zen per-model supportedFormats", () => {
+  it("declares [claude] for Claude + Qwen + union-alpha models", () => {
+    for (const m of CLAUDE_CAPABLE) {
+      expect(getModelSupportedFormats("ocz", m)).toEqual(["claude"]);
+    }
+  });
+
+  it("declares [openai-responses] for GPT/Grok/Spark responses models", () => {
+    for (const m of RESPONSES_CAPABLE) {
+      expect(getModelSupportedFormats("ocz", m)).toEqual(["openai-responses"]);
+    }
+  });
+
+  it("declares [openai] only for chat-only models (GLM/Kimi/MiMo) → guards /messages routing", () => {
+    for (const m of CHAT_ONLY) {
+      expect(getModelSupportedFormats("ocz", m)).toEqual(["openai"]);
+    }
+  });
+});
+
+describe("OpenCode Zen multi-endpoint transports", () => {
+  it("declares openai / claude / openai-responses transports", () => {
+    const formats = (PROVIDERS["opencode-zen"].transports || []).map((t) => t.format);
+    expect(formats).toEqual(["openai", "claude", "openai-responses"]);
+  });
+
+  it("resolveTransport picks the endpoint matching the client sourceFormat", () => {
+    expect(resolveTransport("opencode-zen", "claude").baseUrl).toBe("https://opencode.ai/zen/v1/messages");
+    expect(resolveTransport("opencode-zen", "openai-responses").baseUrl).toBe("https://opencode.ai/zen/v1/responses");
+    expect(resolveTransport("opencode-zen", "openai").baseUrl).toBe("https://opencode.ai/zen/v1/chat/completions");
+  });
+
+  it("uses x-api-key + anthropicVersion on the claude transport", () => {
+    const t = resolveTransport("opencode-zen", "claude");
+    expect(t.auth.header).toBe("x-api-key");
+    expect(t.auth.anthropicVersion).toBe(true);
+  });
+});
+
+describe("OpenCode Zen per-model transport guard (chatCore logic)", () => {
+  it("routes MiniMax/Qwen + claude-format client to /messages", () => {
+    for (const m of CLAUDE_CAPABLE) {
+      expect(pickTransport("opencode-zen", "claude", "ocz", m)?.baseUrl).toBe("https://opencode.ai/zen/v1/messages");
+    }
+  });
+
+  it("does NOT route chat-only models to /messages on a claude-format request", () => {
+    for (const m of CHAT_ONLY) {
+      expect(pickTransport("opencode-zen", "claude", "ocz", m)).toBeNull();
+    }
+  });
+
+  it("routes DeepSeek + responses-format client to /responses", () => {
+    for (const m of RESPONSES_CAPABLE) {
+      expect(pickTransport("opencode-zen", "openai-responses", "ocz", m)?.baseUrl).toBe("https://opencode.ai/zen/v1/responses");
+    }
+  });
+
+  it("routes Muse Spark (responses-only) to /responses, never to /messages", () => {
+    for (const m of ["muse-spark-1.2", "muse-spark-1.3", "muse-spark-1.2-contributor-free", "muse-spark-1.3-contributor-free", "grok-4.6", "gpt-5.6-luna"]) {
+      expect(getModelSupportedFormats("ocz", m)).toEqual(["openai-responses"]);
+      expect(pickTransport("opencode-zen", "openai-responses", "ocz", m)?.baseUrl).toBe("https://opencode.ai/zen/v1/responses");
+      expect(pickTransport("opencode-zen", "claude", "ocz", m)).toBeNull();
+      expect(pickTransport("opencode-zen", "openai", "ocz", m)).toBeNull();
+    }
+  });
+
+  it("does NOT route MiniMax (no responses support) to /responses", () => {
+    for (const m of CLAUDE_CAPABLE) {
+      expect(pickTransport("opencode-zen", "openai-responses", "ocz", m)).toBeNull();
+    }
+  });
+});