diff --git a/canvas/src/components/__tests__/BudgetLimit.DetailsTab.test.tsx b/canvas/src/components/__tests__/BudgetLimit.DetailsTab.test.tsx
index a9515374..6709a996 100644
--- a/canvas/src/components/__tests__/BudgetLimit.DetailsTab.test.tsx
+++ b/canvas/src/components/__tests__/BudgetLimit.DetailsTab.test.tsx
@@ -44,6 +44,15 @@ vi.mock("../tabs/BudgetSection", () => ({
   ),
 }));
 
+// Mock WorkspaceUsage — it has its own test suite (WorkspaceUsage.test.tsx).
+// Without this mock its internal api.get call races against the shared mock
+// and crashes when the return value is not a valid WorkspaceMetrics object.
+vi.mock("../WorkspaceUsage", () => ({
+  WorkspaceUsage: ({ workspaceId }: { workspaceId: string }) => (
+    <div data-testid="workspace-usage-stub" data-ws={workspaceId} />
+  ),
+}));
+
 import { api } from "@/lib/api";
 import { DetailsTab } from "../tabs/DetailsTab";
 
diff --git a/canvas/src/components/__tests__/ClaudeSettings.test.tsx b/canvas/src/components/__tests__/ClaudeSettings.test.tsx
new file mode 100644
index 00000000..b74ab085
--- /dev/null
+++ b/canvas/src/components/__tests__/ClaudeSettings.test.tsx
@@ -0,0 +1,230 @@
+// @vitest-environment jsdom
+/**
+ * Tests for issue #608 — effort + task_budget fields in workspace config.
+ *
+ * Covers:
+ *   1. toYaml serialization (effort + task_budget → YAML keys)
+ *   2. parseYaml round-trip (YAML → ConfigData)
+ *   3. DEFAULT_CONFIG shape (new fields present with zero/empty defaults)
+ *   4. ConfigTab source assertions (section rendered conditionally)
+ *   5. React rendering of the section for claude-code and claude model configs
+ */
+import React from "react";
+import { describe, it, expect, vi, afterEach } from "vitest";
+import { render, screen, cleanup } from "@testing-library/react";
+
+// ── Module-level mocks ───────────────────────────────────────────────────────
+
+vi.mock("@/lib/api", () => ({
+  api: { get: vi.fn(), put: vi.fn(), patch: vi.fn(), post: vi.fn() },
+}));
+
+vi.mock("@/store/canvas", () => ({
+  useCanvasStore: vi.fn(() => ({
+    restartWorkspace: vi.fn(),
+    updateNodeData: vi.fn(),
+  })),
+}));
+
+vi.mock("../tabs/config/secrets-section", () => ({
+  SecretsSection: () => <div data-testid="secrets-stub" />,
+}));
+
+// ── Imports ──────────────────────────────────────────────────────────────────
+
+import { toYaml, parseYaml } from "../tabs/config/yaml-utils";
+import { DEFAULT_CONFIG, type ConfigData } from "../tabs/config/form-inputs";
+import { ConfigTab } from "../tabs/ConfigTab";
+import { api } from "@/lib/api";
+
+afterEach(() => {
+  cleanup();
+  vi.clearAllMocks();
+});
+
+// ── 1. toYaml serialization ──────────────────────────────────────────────────
+
+describe("toYaml — effort field", () => {
+  it("omits effort when empty string", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "" };
+    expect(toYaml(cfg)).not.toContain("effort:");
+  });
+
+  it("omits effort when undefined", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: undefined };
+    expect(toYaml(cfg)).not.toContain("effort:");
+  });
+
+  it("serializes effort: low", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "low" };
+    const yaml = toYaml(cfg);
+    expect(yaml).toContain("effort: low");
+  });
+
+  it("serializes effort: medium", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "medium" };
+    expect(toYaml(cfg)).toContain("effort: medium");
+  });
+
+  it("serializes effort: high", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "high" };
+    expect(toYaml(cfg)).toContain("effort: high");
+  });
+
+  it("serializes effort: xhigh", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "xhigh" };
+    expect(toYaml(cfg)).toContain("effort: xhigh");
+  });
+});
+
+describe("toYaml — task_budget field", () => {
+  it("omits task_budget when 0", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, task_budget: 0 };
+    expect(toYaml(cfg)).not.toContain("task_budget:");
+  });
+
+  it("omits task_budget when undefined", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, task_budget: undefined };
+    expect(toYaml(cfg)).not.toContain("task_budget:");
+  });
+
+  it("serializes task_budget: 10000", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, task_budget: 10000 };
+    expect(toYaml(cfg)).toContain("task_budget: 10000");
+  });
+
+  it("serializes task_budget: 50000", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, task_budget: 50000 };
+    expect(toYaml(cfg)).toContain("task_budget: 50000");
+  });
+});
+
+describe("toYaml — effort and task_budget together", () => {
+  it("serializes both when set", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "xhigh", task_budget: 32000 };
+    const yaml = toYaml(cfg);
+    expect(yaml).toContain("effort: xhigh");
+    expect(yaml).toContain("task_budget: 32000");
+  });
+
+  it("effort appears before task_budget in output", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "high", task_budget: 8000 };
+    const yaml = toYaml(cfg);
+    const effortIdx = yaml.indexOf("effort:");
+    const budgetIdx = yaml.indexOf("task_budget:");
+    expect(effortIdx).toBeGreaterThan(-1);
+    expect(budgetIdx).toBeGreaterThan(-1);
+    expect(effortIdx).toBeLessThan(budgetIdx);
+  });
+});
+
+// ── 2. parseYaml round-trip ──────────────────────────────────────────────────
+
+describe("parseYaml — effort + task_budget round-trip", () => {
+  it("parses effort from YAML", () => {
+    const yaml = "name: Test\neffort: high\n";
+    const parsed = parseYaml(yaml);
+    expect(parsed.effort).toBe("high");
+  });
+
+  it("parses task_budget from YAML as integer", () => {
+    const yaml = "name: Test\ntask_budget: 16000\n";
+    const parsed = parseYaml(yaml);
+    expect(parsed.task_budget).toBe(16000);
+  });
+
+  it("round-trips effort: xhigh through toYaml → parseYaml", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "xhigh" };
+    const yaml = toYaml(cfg);
+    const parsed = parseYaml(yaml);
+    expect(parsed.effort).toBe("xhigh");
+  });
+
+  it("round-trips task_budget: 50000 through toYaml → parseYaml", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, task_budget: 50000 };
+    const yaml = toYaml(cfg);
+    const parsed = parseYaml(yaml);
+    expect(parsed.task_budget).toBe(50000);
+  });
+
+  it("round-trips both fields together", () => {
+    const cfg: ConfigData = { ...DEFAULT_CONFIG, effort: "low", task_budget: 1000 };
+    const yaml = toYaml(cfg);
+    const parsed = parseYaml(yaml);
+    expect(parsed.effort).toBe("low");
+    expect(parsed.task_budget).toBe(1000);
+  });
+});
+
+// ── 3. DEFAULT_CONFIG shape ──────────────────────────────────────────────────
+
+describe("DEFAULT_CONFIG", () => {
+  it("has effort defaulting to empty string", () => {
+    expect(DEFAULT_CONFIG.effort).toBe("");
+  });
+
+  it("has task_budget defaulting to 0", () => {
+    expect(DEFAULT_CONFIG.task_budget).toBe(0);
+  });
+});
+
+// ── 4. ConfigTab source assertions ──────────────────────────────────────────
+
+describe("ConfigTab source — Claude Settings section", () => {
+  it("ConfigTab.tsx contains the effort-select data-testid", async () => {
+    const { readFileSync } = await import("fs");
+    const { join } = await import("path");
+    const src = readFileSync(join(__dirname, "../../components/tabs/ConfigTab.tsx"), "utf8");
+    expect(src).toContain('data-testid="effort-select"');
+    expect(src).toContain('data-testid="task-budget-input"');
+  });
+
+  it("ConfigTab.tsx effort dropdown has all four Claude values", async () => {
+    const { readFileSync } = await import("fs");
+    const { join } = await import("path");
+    const src = readFileSync(join(__dirname, "../../components/tabs/ConfigTab.tsx"), "utf8");
+    expect(src).toContain('"low"');
+    expect(src).toContain('"medium"');
+    expect(src).toContain('"high"');
+    expect(src).toContain('"xhigh"');
+  });
+
+  it("ConfigTab.tsx section is guarded by claude-code runtime check", async () => {
+    const { readFileSync } = await import("fs");
+    const { join } = await import("path");
+    const src = readFileSync(join(__dirname, "../../components/tabs/ConfigTab.tsx"), "utf8");
+    expect(src).toContain('config.runtime === "claude-code"');
+    expect(src).toContain('"claude"');
+  });
+});
+
+// ── 5. React rendering ───────────────────────────────────────────────────────
+
+describe("ConfigTab — Claude Settings section rendering", () => {
+  function setupMock(configYaml: string) {
+    vi.mocked(api.get).mockResolvedValue({ content: configYaml } as never);
+  }
+
+  it("shows Claude Settings section for claude-code runtime", async () => {
+    setupMock("name: Bot\nruntime: claude-code\n");
+    render(<ConfigTab workspaceId="ws-1" />);
+    // Section title appears once loading resolves
+    const section = await screen.findByText("Claude Settings");
+    expect(section).toBeTruthy();
+  });
+
+  it("shows Claude Settings section when model contains claude", async () => {
+    setupMock("name: Bot\nmodel: anthropic:claude-opus-4-7\n");
+    render(<ConfigTab workspaceId="ws-1" />);
+    const section = await screen.findByText("Claude Settings");
+    expect(section).toBeTruthy();
+  });
+
+  it("does NOT show Claude Settings section for non-claude runtime/model", async () => {
+    setupMock("name: Bot\nruntime: crewai\nmodel: openai:gpt-4o\n");
+    render(<ConfigTab workspaceId="ws-1" />);
+    // Wait for load (config.yaml fetch resolves) then check absence
+    await screen.findByText("General"); // loaded
+    expect(screen.queryByText("Claude Settings")).toBeNull();
+  });
+});
diff --git a/canvas/src/components/tabs/ConfigTab.tsx b/canvas/src/components/tabs/ConfigTab.tsx
index 6e600cd4..699ee27a 100644
--- a/canvas/src/components/tabs/ConfigTab.tsx
+++ b/canvas/src/components/tabs/ConfigTab.tsx
@@ -267,6 +267,48 @@ export function ConfigTab({ workspaceId }: Props) {
             <TagList label="Required Env Vars" values={config.runtime_config?.required_env || []} onChange={(v) => updateNested("runtime_config" as keyof ConfigData, "required_env", v)} placeholder="e.g. CLAUDE_CODE_OAUTH_TOKEN" />
           </Section>
 
+          {/* Claude Settings — shown for claude-code runtime or claude/anthropic model names */}
+          {(config.runtime === "claude-code" ||
+            (config.runtime_config?.model || config.model || "").toLowerCase().includes("claude") ||
+            (config.runtime_config?.model || config.model || "").toLowerCase().includes("anthropic")) && (
+            <Section title="Claude Settings" defaultOpen={false}>
+              <div>
+                <label className="text-[10px] text-zinc-500 block mb-1">
+                  Effort
+                  <span className="ml-1 text-zinc-600">(output_config.effort — Opus 4.7+)</span>
+                </label>
+                <select
+                  value={config.effort || ""}
+                  onChange={(e) => update("effort", e.target.value)}
+                  className="w-full bg-zinc-800 border border-zinc-700 rounded px-2 py-1 text-xs text-zinc-200 focus:outline-none focus:border-blue-500"
+                  data-testid="effort-select"
+                >
+                  <option value="">— unset (model default) —</option>
+                  <option value="low">low</option>
+                  <option value="medium">medium</option>
+                  <option value="high">high</option>
+                  <option value="xhigh">xhigh (extended thinking)</option>
+                </select>
+              </div>
+              <div>
+                <label className="text-[10px] text-zinc-500 block mb-1">
+                  Task Budget (tokens)
+                  <span className="ml-1 text-zinc-600">(output_config.task_budget.total — 0 = unset)</span>
+                </label>
+                <input
+                  type="number"
+                  min={0}
+                  step={1000}
+                  value={config.task_budget ?? 0}
+                  onChange={(e) => update("task_budget", parseInt(e.target.value, 10) || 0)}
+                  placeholder="0"
+                  className="w-full bg-zinc-800 border border-zinc-700 rounded px-2 py-1 text-xs text-zinc-200 focus:outline-none focus:border-blue-500 font-mono"
+                  data-testid="task-budget-input"
+                />
+              </div>
+            </Section>
+          )}
+
           <Section title="Skills & Tools" defaultOpen={false}>
             <TagList label="Skills" values={config.skills || []} onChange={(v) => update("skills", v)} placeholder="e.g. code-review" />
             <TagList label="Tools" values={config.tools || []} onChange={(v) => update("tools", v)} placeholder="e.g. web_search, filesystem" />
diff --git a/canvas/src/components/tabs/config/form-inputs.tsx b/canvas/src/components/tabs/config/form-inputs.tsx
index 63e983d6..58c75101 100644
--- a/canvas/src/components/tabs/config/form-inputs.tsx
+++ b/canvas/src/components/tabs/config/form-inputs.tsx
@@ -16,6 +16,11 @@ export interface ConfigData {
     // Deprecated
     auth_token_file?: string;
   };
+  // Claude API primitives (Opus 4.7+) — issue #608
+  // effort maps to output_config.effort in Messages API: 'low' | 'medium' | 'high' | 'xhigh'
+  effort?: string;
+  // task_budget maps to output_config.task_budget.total (requires beta header task-budgets-2026-03-13)
+  task_budget?: number;
   prompt_files: string[];
   shared_context: string[];
   skills: string[];
@@ -32,6 +37,8 @@ export const DEFAULT_CONFIG: ConfigData = {
   tier: 1,
   model: "",
   runtime: "",
+  effort: "",
+  task_budget: 0,
   prompt_files: [],
   shared_context: [],
   skills: [],
diff --git a/canvas/src/components/tabs/config/yaml-utils.ts b/canvas/src/components/tabs/config/yaml-utils.ts
index 752bd7ab..77ffff2d 100644
--- a/canvas/src/components/tabs/config/yaml-utils.ts
+++ b/canvas/src/components/tabs/config/yaml-utils.ts
@@ -116,6 +116,9 @@ export function toYaml(config: ConfigData): string {
     }
   }
   if (config.model) { lines.push(""); simple("model", config.model); }
+  // Claude API primitives (issue #608)
+  if (config.effort) { lines.push(""); simple("effort", config.effort); }
+  if (config.task_budget && config.task_budget > 0) { simple("task_budget", config.task_budget); }
   if (config.prompt_files?.length) { lines.push(""); list("prompt_files", config.prompt_files); }
   if (config.shared_context?.length) { lines.push(""); list("shared_context", config.shared_context); }
   lines.push(""); list("skills", config.skills);