diff --git a/packages/adapter-utils/src/types.ts b/packages/adapter-utils/src/types.ts
index ce89e0e8..79171cbd 100644
--- a/packages/adapter-utils/src/types.ts
+++ b/packages/adapter-utils/src/types.ts
@@ -344,6 +344,7 @@ export interface CreateConfigValues {
   workspaceBranchTemplate?: string;
   worktreeParentDir?: string;
   runtimeServicesJson?: string;
+  billingMode?: string;
   maxTurnsPerRun: number;
   heartbeatEnabled: boolean;
   intervalSec: number;
diff --git a/packages/adapters/opencode-local/src/server/execute.ts b/packages/adapters/opencode-local/src/server/execute.ts
index 94d7f967..330da070 100644
--- a/packages/adapters/opencode-local/src/server/execute.ts
+++ b/packages/adapters/opencode-local/src/server/execute.ts
@@ -372,7 +372,10 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
       provider: parseModelProvider(modelId),
       biller: resolveOpenCodeBiller(runtimeEnv, parseModelProvider(modelId)),
       model: modelId,
-      billingType: applyBillingModeOverride("api", asString(config.billingMode, "auto")) === "subscription" ? "subscription" : "unknown",
+      billingType: (() => {
+        const mode = asString(config.billingMode, "auto").trim().toLowerCase();
+        return mode === "auto" || mode === "" ? "unknown" : applyBillingModeOverride("api", mode);
+      })(),
       costUsd: attempt.parsed.costUsd,
       resultJson: {
         stdout: attempt.proc.stdout,
diff --git a/packages/adapters/pi-local/src/server/execute.ts b/packages/adapters/pi-local/src/server/execute.ts
index 6dc50219..296d6560 100644
--- a/packages/adapters/pi-local/src/server/execute.ts
+++ b/packages/adapters/pi-local/src/server/execute.ts
@@ -461,7 +461,10 @@ export async function execute(ctx: AdapterExecutionContext): Promise<AdapterExec
       provider: provider,
       biller: resolvePiBiller(runtimeEnv, provider),
       model: model,
-      billingType: applyBillingModeOverride("api", asString(config.billingMode, "auto")) === "subscription" ? "subscription" : "unknown",
+      billingType: (() => {
+        const mode = asString(config.billingMode, "auto").trim().toLowerCase();
+        return mode === "auto" || mode === "" ? "unknown" : applyBillingModeOverride("api", mode);
+      })(),
       costUsd: attempt.parsed.usage.costUsd,
       resultJson: {
         stdout: attempt.proc.stdout,
diff --git a/server/src/__tests__/billing-mode-override.test.ts b/server/src/__tests__/billing-mode-override.test.ts
index 571ddd7a..bbf2af91 100644
--- a/server/src/__tests__/billing-mode-override.test.ts
+++ b/server/src/__tests__/billing-mode-override.test.ts
@@ -37,3 +37,32 @@ describe("applyBillingModeOverride", () => {
     expect(applyBillingModeOverride("subscription", "credits")).toBe("subscription");
   });
 });
+
+describe("pi/opencode billing mode pattern (unknown-default adapters)", () => {
+  // Mirrors the inline pattern used in pi-local and opencode-local where
+  // the default billing type is "unknown" (no auto-detection available).
+  function resolveUnknownDefault(billingMode: string): string {
+    const mode = billingMode.trim().toLowerCase();
+    return mode === "auto" || mode === "" ? "unknown" : applyBillingModeOverride("api", mode);
+  }
+
+  it("returns 'unknown' when billingMode is 'auto' (default)", () => {
+    expect(resolveUnknownDefault("auto")).toBe("unknown");
+  });
+
+  it("returns 'unknown' when billingMode is empty", () => {
+    expect(resolveUnknownDefault("")).toBe("unknown");
+  });
+
+  it("returns 'subscription' when billingMode is 'subscription'", () => {
+    expect(resolveUnknownDefault("subscription")).toBe("subscription");
+  });
+
+  it("returns 'api' when billingMode is 'metered'", () => {
+    expect(resolveUnknownDefault("metered")).toBe("api");
+  });
+
+  it("returns 'api' when billingMode is 'api'", () => {
+    expect(resolveUnknownDefault("api")).toBe("api");
+  });
+});
diff --git a/ui/src/adapters/billing-mode-field.tsx b/ui/src/adapters/billing-mode-field.tsx
new file mode 100644
index 00000000..f72f328d
--- /dev/null
+++ b/ui/src/adapters/billing-mode-field.tsx
@@ -0,0 +1,36 @@
+import type { AdapterConfigFieldsProps } from "./types";
+import { Field, help } from "../components/agent-config-primitives";
+
+const selectClass =
+  "w-full rounded-md border border-border px-2.5 py-1.5 bg-transparent outline-none text-sm font-mono";
+
+export function BillingModeField({
+  isCreate,
+  values,
+  set,
+  config,
+  eff,
+  mark,
+}: Pick<AdapterConfigFieldsProps, "isCreate" | "values" | "set" | "config" | "eff" | "mark">) {
+  const value = isCreate
+    ? String(values?.billingMode ?? "auto")
+    : eff("adapterConfig", "billingMode", String(config.billingMode ?? "auto"));
+
+  return (
+    <Field label="Billing mode" hint={help.billingMode}>
+      <select
+        value={value}
+        onChange={(e) =>
+          isCreate
+            ? set?.({ billingMode: e.target.value })
+            : mark("adapterConfig", "billingMode", e.target.value === "auto" ? undefined : e.target.value)
+        }
+        className={selectClass}
+      >
+        <option value="auto">Auto (detect from API keys)</option>
+        <option value="subscription">Subscription (non-billable)</option>
+        <option value="metered">Metered API (billable)</option>
+      </select>
+    </Field>
+  );
+}
diff --git a/ui/src/components/AgentConfigForm.tsx b/ui/src/components/AgentConfigForm.tsx
index 1810e9a8..f5eb8f2c 100644
--- a/ui/src/components/AgentConfigForm.tsx
+++ b/ui/src/components/AgentConfigForm.tsx
@@ -41,6 +41,7 @@ import {
 import { defaultCreateValues } from "./agent-config-defaults";
 import { getUIAdapter } from "../adapters";
 import { ClaudeLocalAdvancedFields } from "../adapters/claude-local/config-fields";
+import { BillingModeField } from "../adapters/billing-mode-field";
 import { MarkdownEditor } from "./MarkdownEditor";
 import { ChoosePathButton } from "./PathInstructionsModal";
 import { OpenCodeLogoIcon } from "./OpenCodeLogoIcon";
@@ -773,6 +774,8 @@ export function AgentConfigForm(props: AgentConfigFormProps) {
                 <ClaudeLocalAdvancedFields {...adapterFieldProps} />
               )}
 
+              <BillingModeField {...adapterFieldProps} />
+
               <Field label="Extra args (comma-separated)" hint={help.extraArgs}>
                 <DraftInput
                   value={
diff --git a/ui/src/components/agent-config-primitives.tsx b/ui/src/components/agent-config-primitives.tsx
index 3c0fd25b..1985a293 100644
--- a/ui/src/components/agent-config-primitives.tsx
+++ b/ui/src/components/agent-config-primitives.tsx
@@ -55,6 +55,7 @@ export const help: Record<string, string> = {
   cooldownSec: "Minimum seconds between consecutive heartbeat runs.",
   maxConcurrentRuns: "Maximum number of heartbeat runs that can execute simultaneously for this agent.",
   budgetMonthlyCents: "Monthly spending limit in cents. 0 means no limit.",
+  billingMode: "Controls how runs are billed. Auto detects from API keys. Set to Subscription if you're on a plan (e.g. Claude Max, GPT Plus) so runs don't count toward spend.",
 };
 
 export const adapterLabels: Record<string, string> = {