diff --git a/src/commands/run.tsx b/src/commands/run.tsx
index 457a5ab..7657037 100644
--- a/src/commands/run.tsx
+++ b/src/commands/run.tsx
@@ -43,7 +43,11 @@ export function registerRun(program: Command): void {
       '-t, --template <slug>',
       'start from a maintained run template (e.g. welcome-to-ellipsis)',
     )
-    .option('-b, --budget <usd>', 'per-run budget override in USD', parseFloat)
+    .option(
+      '-b, --budget <usd>',
+      "per-run budget override in USD (sets the config's limits.run for this run)",
+      parseFloat,
+    )
     .option(
       '-m, --metadata <key=value>',
       'attach metadata (repeatable)',
@@ -81,7 +85,11 @@ export function registerRun(program: Command): void {
           if (opts.config) req.config_id = opts.config
           if (opts.configFile) req.config = readJsonFile(opts.configFile)
           if (opts.template) req.template_id = opts.template
-          if (opts.budget !== undefined) req.budget_usd = opts.budget
+          // A budget is expressed as a config override of limits.run (the server
+          // merges it onto the chosen config and re-validates).
+          if (opts.budget !== undefined) {
+            req.config_override_yaml = `limits:\n  run: ${opts.budget}`
+          }
 
           const api = new ApiClient()
           const run = await api.startAgentRun(req)
diff --git a/src/lib/types.ts b/src/lib/types.ts
index f24a353..aa214bc 100644
--- a/src/lib/types.ts
+++ b/src/lib/types.ts
@@ -132,7 +132,10 @@ export interface StartAgentRunRequest {
   template_id?: string
   source?: AgentRunSource
   metadata?: Record<string, string>
-  budget_usd?: number
+  // A partial agent config (YAML) merged onto the chosen config and re-validated
+  // server-side, e.g. "limits:\n  run: 5.0" to set just this run's budget. Only
+  // meaningful with config_id/template_id.
+  config_override_yaml?: string
 }
 
 export interface ListAgentRunsResponse {