diff --git a/packages/ai/src/providers/anthropic.ts b/packages/ai/src/providers/anthropic.ts
index b5a8778e..f39c6e6e 100644
--- a/packages/ai/src/providers/anthropic.ts
+++ b/packages/ai/src/providers/anthropic.ts
@@ -31,18 +31,33 @@ import { transformMessages } from "./transform-messages.js";
 // Stealth mode: Mimic Claude Code's tool naming exactly
 const claudeCodeVersion = "2.1.2";
 
-// Map pi! tool names to Claude Code's exact tool names
-const claudeCodeToolNames: Record<string, string> = {
-	read: "Read",
-	write: "Write",
-	edit: "Edit",
-	bash: "Bash",
-	grep: "Grep",
-	find: "Glob",
-	ls: "Ls",
-};
+// Claude Code 2.x tool names (canonical casing)
+// Source: https://cchistory.mariozechner.at/data/prompts-2.1.11.md
+// To update: https://github.com/badlogic/cchistory
+const claudeCodeTools = [
+	"Read",
+	"Write",
+	"Edit",
+	"Bash",
+	"Grep",
+	"Glob",
+	"AskUserQuestion",
+	"EnterPlanMode",
+	"ExitPlanMode",
+	"KillShell",
+	"NotebookEdit",
+	"Skill",
+	"Task",
+	"TaskOutput",
+	"TodoWrite",
+	"WebFetch",
+	"WebSearch",
+];
 
-const toClaudeCodeName = (name: string) => claudeCodeToolNames[name] || name;
+const ccToolLookup = new Map(claudeCodeTools.map((t) => [t.toLowerCase(), t]));
+
+// Convert tool name to CC canonical casing if it matches (case-insensitive)
+const toClaudeCodeName = (name: string) => ccToolLookup.get(name.toLowerCase()) ?? name;
 const fromClaudeCodeName = (name: string, tools?: Tool[]) => {
 	if (tools && tools.length > 0) {
 		const lowerName = name.toLowerCase();
diff --git a/packages/ai/test/anthropic-tool-name-normalization.test.ts b/packages/ai/test/anthropic-tool-name-normalization.test.ts
new file mode 100644
index 00000000..93241b5f
--- /dev/null
+++ b/packages/ai/test/anthropic-tool-name-normalization.test.ts
@@ -0,0 +1,205 @@
+import { Type } from "@sinclair/typebox";
+import { describe, expect, it } from "vitest";
+import { getModel } from "../src/models.js";
+import { stream } from "../src/stream.js";
+import type { Context, Tool } from "../src/types.js";
+import { resolveApiKey } from "./oauth.js";
+
+const oauthToken = await resolveApiKey("anthropic");
+
+/**
+ * Tests for Anthropic OAuth tool name normalization.
+ *
+ * When using Claude Code OAuth, tool names must match CC's canonical casing.
+ * The normalization should:
+ * 1. Convert tool names that match CC tools (case-insensitive) to CC casing on outbound
+ * 2. Convert tool names back to the original casing on inbound
+ *
+ * This is a simple case-insensitive lookup, NOT a mapping of different names.
+ * e.g., "todowrite" -> "TodoWrite" -> "todowrite" (round-trip works)
+ *
+ * The old `find -> Glob` mapping was WRONG because:
+ * - Outbound: "find" -> "Glob"
+ * - Inbound: "Glob" -> ??? (no tool named "glob" in context.tools, only "find")
+ * - Result: tool call has name "Glob" but no tool exists with that name
+ */
+describe.skipIf(!oauthToken)("Anthropic OAuth tool name normalization", () => {
+	const model = getModel("anthropic", "claude-sonnet-4-20250514");
+
+	it("should normalize user-defined tool matching CC name (todowrite -> TodoWrite -> todowrite)", async () => {
+		// User defines a tool named "todowrite" (lowercase)
+		// CC has "TodoWrite" - this should round-trip correctly
+		const todoTool: Tool = {
+			name: "todowrite",
+			description: "Write a todo item",
+			parameters: Type.Object({
+				task: Type.String({ description: "The task to add" }),
+			}),
+		};
+
+		const context: Context = {
+			systemPrompt: "You are a helpful assistant. Use the todowrite tool when asked to add todos.",
+			messages: [
+				{
+					role: "user",
+					content: "Add a todo: buy milk. Use the todowrite tool.",
+					timestamp: Date.now(),
+				},
+			],
+			tools: [todoTool],
+		};
+
+		const s = stream(model, context, { apiKey: oauthToken });
+		let toolCallName: string | undefined;
+
+		for await (const event of s) {
+			if (event.type === "toolcall_end") {
+				const toolCall = event.partial.content[event.contentIndex];
+				if (toolCall.type === "toolCall") {
+					toolCallName = toolCall.name;
+				}
+			}
+		}
+
+		const response = await s.result();
+		expect(response.stopReason, `Error: ${response.errorMessage}`).toBe("toolUse");
+
+		// The tool call should come back with the ORIGINAL name "todowrite", not "TodoWrite"
+		expect(toolCallName).toBe("todowrite");
+	});
+
+	it("should handle pi's built-in tools (read, write, edit, bash)", async () => {
+		// Pi's tools use lowercase names, CC uses PascalCase
+		const readTool: Tool = {
+			name: "read",
+			description: "Read a file",
+			parameters: Type.Object({
+				path: Type.String({ description: "File path" }),
+			}),
+		};
+
+		const context: Context = {
+			systemPrompt: "You are a helpful assistant. Use the read tool to read files.",
+			messages: [
+				{
+					role: "user",
+					content: "Read the file /tmp/test.txt using the read tool.",
+					timestamp: Date.now(),
+				},
+			],
+			tools: [readTool],
+		};
+
+		const s = stream(model, context, { apiKey: oauthToken });
+		let toolCallName: string | undefined;
+
+		for await (const event of s) {
+			if (event.type === "toolcall_end") {
+				const toolCall = event.partial.content[event.contentIndex];
+				if (toolCall.type === "toolCall") {
+					toolCallName = toolCall.name;
+				}
+			}
+		}
+
+		const response = await s.result();
+		expect(response.stopReason, `Error: ${response.errorMessage}`).toBe("toolUse");
+
+		// The tool call should come back with the ORIGINAL name "read", not "Read"
+		expect(toolCallName).toBe("read");
+	});
+
+	it("should NOT map find to Glob - find is not a CC tool name", async () => {
+		// Pi has a "find" tool, CC has "Glob" - these are DIFFERENT tools
+		// The old code incorrectly mapped find -> Glob, which broke the round-trip
+		// because there's no tool named "glob" in context.tools
+		const findTool: Tool = {
+			name: "find",
+			description: "Find files by pattern",
+			parameters: Type.Object({
+				pattern: Type.String({ description: "Glob pattern" }),
+			}),
+		};
+
+		const context: Context = {
+			systemPrompt: "You are a helpful assistant. Use the find tool to search for files.",
+			messages: [
+				{
+					role: "user",
+					content: "Find all .ts files using the find tool.",
+					timestamp: Date.now(),
+				},
+			],
+			tools: [findTool],
+		};
+
+		const s = stream(model, context, { apiKey: oauthToken });
+		let toolCallName: string | undefined;
+
+		for await (const event of s) {
+			if (event.type === "toolcall_end") {
+				const toolCall = event.partial.content[event.contentIndex];
+				if (toolCall.type === "toolCall") {
+					toolCallName = toolCall.name;
+				}
+			}
+		}
+
+		const response = await s.result();
+		expect(response.stopReason, `Error: ${response.errorMessage}`).toBe("toolUse");
+
+		// With the BROKEN find -> Glob mapping:
+		// - Sent as "Glob" to Anthropic
+		// - Received back as "Glob"
+		// - fromClaudeCodeName("Glob", tools) looks for tool.name.toLowerCase() === "glob"
+		// - No match (tool is named "find"), returns "Glob"
+		// - Test fails: toolCallName is "Glob" instead of "find"
+		//
+		// With the CORRECT implementation (no find->Glob mapping):
+		// - Sent as "find" to Anthropic (no CC tool named "Find")
+		// - Received back as "find"
+		// - Test passes: toolCallName is "find"
+		expect(toolCallName).toBe("find");
+	});
+
+	it("should handle custom tools that don't match any CC tool names", async () => {
+		// A completely custom tool should pass through unchanged
+		const customTool: Tool = {
+			name: "my_custom_tool",
+			description: "A custom tool",
+			parameters: Type.Object({
+				input: Type.String({ description: "Input value" }),
+			}),
+		};
+
+		const context: Context = {
+			systemPrompt: "You are a helpful assistant. Use my_custom_tool when asked.",
+			messages: [
+				{
+					role: "user",
+					content: "Use my_custom_tool with input 'hello'.",
+					timestamp: Date.now(),
+				},
+			],
+			tools: [customTool],
+		};
+
+		const s = stream(model, context, { apiKey: oauthToken });
+		let toolCallName: string | undefined;
+
+		for await (const event of s) {
+			if (event.type === "toolcall_end") {
+				const toolCall = event.partial.content[event.contentIndex];
+				if (toolCall.type === "toolCall") {
+					toolCallName = toolCall.name;
+				}
+			}
+		}
+
+		const response = await s.result();
+		expect(response.stopReason, `Error: ${response.errorMessage}`).toBe("toolUse");
+
+		// Custom tool names should pass through unchanged
+		expect(toolCallName).toBe("my_custom_tool");
+	});
+});